US20100290308A1 - Systems using a levitating, rotating pumping or mixing element and related methods - Google Patents

Abstract

A system for pumping or mixing a fluid using a rotating pumping or mixing element and various other components for use in a pumping or mixing system are disclosed.

Description

• This application is a continuation of Ser. No. 12/250,180, which is: (1) a continuation of Ser. No. 11/496,702, filed Jul. 31, 2006, and now U.S. Pat. No. 7,434,983, which is a continuation of Ser. No. 10/398,946, which is the national stage of PCT/US01/31459, filed Oct. 9, 2001, now U.S. Pat. No. 7,086,778, which claims the benefit of the following U.S. Provisional Patent Applications: (a) Ser. No. 60/239,187. filed Oct. 9, 2000; (b) Ser. No. 60/282,927, filed Apr. 10, 2001; and (c) Ser. No. 60/318,579, filed Sep. 11, 2001; and (2) a continuation-in-part of Ser. No. 10/491,512, which is the national stage of PCT/US02/31478, filed Oct. 2, 2002, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/326,833, filed Oct. 3, 2001. This application is a continuation-in-part of Ser. No. 11/298,406, which is a continuation-in-part of U.S. patent application Ser. No. 10/491,512 and claims the benefit of U.S. Provisional Patent Application Ser. No. 60/634,664, filed Dec. 9, 2004. The entire disclosures of the foregoing applications are all incorporated herein by reference.
TECHNICAL FIELD
• The present invention relates generally to the mixing arts and, more particularly, to a system, related components, and related method for pumping or mixing fluids using a rotatable magnetic element.
BACKGROUND OF THE INVENTION
• Most pharmaceutical solutions and suspensions manufactured on an industrial scale require highly controlled, thorough mixing to achieve a satisfactory yield and ensure a uniform distribution of ingredients in the final product. Agitator tanks are frequently used to complete the mixing process, but a better degree of mixing is normally achieved by using a mechanical stirrer or impeller (e.g., a set of mixing blades attached to a metal rod). Typically, the mechanical stirrer or impeller is simply lowered into the fluid through an opening in the top of the vessel and rotated by an external motor to create the desired mixing action.
• One significant limitation or shortcoming of such an arrangement is the danger of contamination or leakage during mixing. The rod carrying the mixing blades or impeller is typically introduced into the vessel through a dynamic seal or bearing. This opening provides an opportunity for bacteria or other contaminants to enter, which of course can lead to the degradation of the product. A corresponding danger of environmental contamination exists in applications involving hazardous or toxic fluids, or suspensions of pathogenic organisms, since dynamic seals or bearings are prone to leakage. Cleanup and sterilization are also made difficult by the dynamic bearings or seals, since these structures typically include folds and crevices that are difficult to reach. Since these problems are faced by all manufacturers of sterile solutions, pharmaceuticals, or the like, the U.S. Food and Drug Administration (FDA) has consequently promulgated strict processing requirements for such fluids, and especially those slated for intravenous use.
• Recently, there has also been an extraordinary increase in the use of biosynthetic pathways in the production of pharmaceutical materials, but problems plague those involved in this rapidly advancing industry. The primary problem is that suspensions of genetically altered bacterial cells frequently used to produce protein pharmaceuticals (insulin is a well-known example) require gentle mixing to circulate nutrients. If overly vigorous mixing or contact between the impeller and the vessel wall occurs, the resultant forces and shear stresses may damage or destroy a significant fraction of the cells, as well as protein molecules that are sensitive to shear stresses. This not only reduces the beneficial yield of the process, but also creates deleterious debris in the fluid suspension that requires further processing to remove.
• In an effort to overcome this problem, others have proposed alternative mixing technologies. The most common proposal for stirring fluids under sterile conditions is to use a rotating, permanent magnet bar covered by an inert layer of TEFLON, glass, or the like. The magnetic bar is placed on the bottom of the agitator vessel and rotated by a driving magnet positioned external to the vessel. Of course, the use of such an externally driven magnetic bar avoids the need for a dynamic bearing, seal or other opening in the vessel to transfer the rotational force from the driving magnet to the stirring magnet. Therefore, a completely enclosed system is provided. This of course prevents leakage and the potential for contamination created by hazardous materials (e.g., cytotoxic agents, solvents with low flash points, blood products, etc.), eases clean up, and allows for the desirable sterile interior environment to be maintained. However, several well-recognized drawbacks are associated with this mixing technology, making it unacceptable for use in many applications. For example, the driving magnet produces not only torque on the stirring magnetic bar, but also an attractive axial thrust force tending to drive the bar into contact with the bottom wall of the vessel. This of course generates substantial friction at the interface between the bar and the bottom wall of the vessel. This uncontrolled friction generates unwanted heat and may also introduce an undesirable shear stress in the fluid. Consequently, fragile biological molecules, such as proteins and living cells that are highly sensitive to temperature and shear stress, are easily damaged during the mixing process, and the resultant debris may contaminate the product. Moreover, the magnetic bar stirrer may not generate the level of circulation provided by an impeller, and thus cannot be scaled up to provide effective mixing throughout the entire volume of large agitation tanks of the type preferred in commercial production operations.
• In yet another effort to eliminate the need for dynamic bearings or shaft seals, some have proposed mixing vessels having external magnets that remotely couple the mixing impeller to a motor located externally to the vessel. A typical magnetic coupler comprises a drive magnet attached to the motor and a stirring magnet carrying an impeller. Similar to the magnetic bar technology described above, the driver and stirrer magnets are kept in close proximity to ensure that the coupling between the two is strong enough to provide sufficient torque. An example of one such proposal is found in U.S. Pat. No. 5,470,152 to Rains.
• As described above, the high torque generated can drive the impeller into the walls of the vessel creating significant friction. By strategically positioning roller bearings inside the vessel, the effects of friction between the impeller and the vessel wall can be substantially reduced. Of course, high stresses at the interfaces between the ball bearings and the vessel wall or impeller result in a grinding of the mixing proteins and living cells, and loss of yield. Further, the bearings may be sensitive to corrosive reactions with water-based solutions and other media and will eventually deteriorate, resulting in frictional losses that slow the impeller, reduce the mixing action, and eventually also lead to undesirable contamination of the product. Mechanical bearings also add to the cleanup problems.
• In an effort to address and overcome the limitations described above, still others have proposed levitated pumping or mixing elements designed to reduce the deleterious effects of friction resulting from magnetically coupled mixers. By using a specially configured magnetic coupler to maintain only a repulsive levitation force in the vertical direction, the large thrust force between the stirring and driving magnets can be eliminated, along with the resultant shear stress and frictional heating. An example of one such arrangement is shown in U.S. Pat. No. 5,478,149 to Quigg.
• However, one limitation remaining from this approach is that only magnet-magnet interactions provide the levitation. This leads to intrinsically unstable systems that produce the desired levitation in the vertical direction, but are unable to control side-to-side movement. As a result, external contact bearings in the form of bearing rings are necessary to laterally stabilize the impeller. Although this “partial” levitation reduces the friction between the impeller and the vessel walls, it does not totally eliminate the drawbacks of the magnetically coupled, roller bearing mixers previously mentioned.
• In an attempt to eliminate the need for contact or other types of mechanical roller bearings, complex feedback control has been proposed to stabilize the impeller. Typical arrangements use electromagnets positioned alongside the levitating magnet. However, the high power level required to attain only sub-millimeter separations between the levitating magnet and the stabilizing magnets constitutes a major disadvantage of this approach. Furthermore, this solution is quite complex, since the stabilizing magnets must be actively monitored and precisely controlled by complex computer-implemented software routines to achieve even a moderate degree of stability. As a consequence of this complexity and the associated maintenance expense, this ostensible solution has not been accepted in the commercial arena, and it is doubtful that it can be successfully scaled up for use in mixing industrial or commercial scale process volumes.
• Thus, a need is identified for a system having a magnetic element for pumping or mixing fluids, and especially ultra-pure, hazardous, or delicate fluid solutions or suspensions, including those which may be processed in vessels capable of withstanding high pressurization. The system would preferably employ a magnetic element capable of pumping or mixing a fluid that levitates in a stable fashion in the vessel to avoid contact with the bottom or side walls thereof when in use. No mixing rod or other structure penetrating the mixing vessel would be required, which of course eliminates the need for dynamic bearings or seals and all potentially deleterious effects associated therewith. Also, the use of a levitating magnetic element would eliminate the need for mechanical bearings or the deleterious magnet-wall interactions that create undesirable shear stresses and unwanted friction in the fluid. Since penetration is unnecessary, the vessel could be completely sealed prior to mixing, and possibly even pressurized. This would reduce the chance for external exposure in the case of hazardous or biological fluids, such as blood or the like, or contamination, in the case of biologically active or sensitive products. The vessel and pumping or mixing element could also possibly be made of disposable materials, such as inexpensive, flexible plastic materials, and discarded after each use to eliminate the need for cleaning or sterilization.
SUMMARY OF THE INVENTION
• A mixing apparatus comprising a flexible bag including an interior compartment for receiving a fluid, said bag including a cavity bounded by a wall projecting into the interior compartment, a mixing element in the interior compartment of the bag adjacent to the wall of the cavity, and a motive device adapted for insertion into the cavity for moving the mixing element.
• In one embodiment, the motive device comprises a rotating shaft. The mixing element may form a non-contact coupling with the motive device. The mixing element may comprise at least one magnet. The wall may comprise a flexible sleeve. The motive device may be adapted to be electrically coupled to a power source. The mixing element may comprise at least one blade. The apparatus may further include a rigid container for supporting the bag. A surface on the wall in the interior compartment may be adapted for engaging a matching surface of the mixing element.
• A mixing apparatus, comprises a container having a transparent sidewall at least partially defining an interior compartment for the mixing of media, said container including a cavity bounded by a wall projecting into the interior compartment, a mixing element in the container adjacent to the wall of the cavity, and a motive device for moving the mixing element.
• In one embodiment, the wall projects into the interior compartment from other than a floor of the container. The wall may project into the interior compartment from an upper portion of the container. The container may comprise a flexible bag. The mixing element may comprise an opening for receiving the wall forming the cavity. The mixing element may further comprise an inner surface adapted for engaging a surface of the wall.
• A mixing apparatus comprising a container including an interior compartment for receiving a fluid, a mixing element in the interior compartment of the container and capable of spinning about an axis, and a tubular shaft projecting into the interior compartment and adapted for moving the mixing element, said tubular shaft including a cavity having a rigid rod positioned therein.
• In one embodiment, the container comprises a flexible bag. The tubular shaft may comprise a flexible sleeve. The tubular shaft may be adapted to rotate relative to the flexible bag. A motive device may be provided for rotating the tubular shaft. The tubular shaft may be associated with at least one bearing.
BRIEF DESCRIPTION OF THE DRAWINGS
• The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description. assist in explaining the principles of the invention. In the drawings:
• FIG. 1 is a partially cross-sectional, partially cutaway, partially schematic view of one embodiment of the system of the present invention wherein the levitating pumping or mixing element is rotated by an external drive or driving magnet to mix a fluid in a vessel and the cooling source is a separate cooling chamber defined by the outer wall of a cryostat holding a cryogen;
• FIG. 2 is an enlarged cross-sectional, partially cutaway, partially schematic view of an embodiment wherein the rotating, levitating pumping or mixing element is used to pump a fluid through a vessel positioned adjacent to the housing for the superconducting element and the cooling source is a closed cycle refrigerator;
• FIG. 3 is a partially cross-sectional, partially cutaway, partially schematic view of the system of the first embodiment wherein the superconducting element, vessel, pumping or mixing element, and drive magnet are axially aligned, but moved off-center relative to the vertical center axis of the vessel;
• FIG. 4ais a bottom view of the drive magnet used in situations where exceptional rotational stability of the pumping or mixing element of the preferred embodiment is required;
• FIG. 4bis a partially cross-sectional, partially cutaway side view of the system showing the drive magnet ofFIG. 4amagnetically coupled to a similarly constructed second permanent magnet forming a part of the pumping or mixing element;
• FIG. 4cis one possible embodiment of the pumping or mixing system including a pumping or mixing element having a chamber for holding a substance that is lighter than the surrounding fluid, such as air, that assists in levitating the pumping or mixing element;
• FIG. 5 is a partially cross-sectional, partially schematic side view of a second possible embodiment of a pumping or mixing system using a pumping or mixing element levitated by a thermally isolated cold superconducting element wherein the motive force for rotating the pumping or mixing element in the vessel is provided by rotating the superconducting element itself;
• FIG. 6ais a top schematic view of one possible arrangement of the levitating pumping or mixing element that may be driven by a rotating superconducting element;
• FIG. 6bshows the pumping or mixing element ofFIG. 6alevitating above a rotating superconducting element formed of two component parts;
• FIG. 7 is a partially cutaway, partially cross-sectional schematic side view of a vessel in the form of a centrifugal pumping head, including a levitating, rotating pumping or mixing element for pumping fluid from the inlet to the outlet of the centrifugal pumping head;
• FIG. 8ashows an alternate embodiment of a pumping or mixing element especially adapted for levitation in a vessel or container having a relatively narrow opening;
• FIG. 8bshows another alternate embodiment of a pumping or mixing element adapted especially for use in a vessel or container having a relatively narrow opening;
• FIG. 8cillustrates the pumping or mixing element ofFIG. 8bin a partially folded state for insertion in the narrow opening of a vessel or container;
• FIG. 9 is a partially cross-sectional, partially schematic side view of a second embodiment of a pumping or mixing system wherein separate levitating and driven magnets are carried on the same, low-profile pumping or mixing element, with the levitation being supplied by a thermally isolated superconducting element and the rotary motion being supplied a motive device including driving magnets coupled to a rotating shaft and positioned in an opening in the evacuated or insulated chamber surrounding the superconducting element;
• FIG. 9ais a top or bottom view of one possible embodiment of a pumping or mixing element for use in the system ofFIG. 9;
• FIG. 9bis a partially cross-sectional side view of the pumping or mixing element ofFIGS. 9 and 9alevitating above the superconducting element, and illustrating the manner in which the driven magnets are coupled to the corresponding driving magnets to create the desired rotational motion;
• FIG. 10 is a top view of a most preferred version of a cryostat for use with the pumping and mixing system of the embodiment ofFIG. 9;
• FIG. 11 is a partially cutaway, partially cross-sectional side schematic view of a centrifugal pumping head for use with the system ofFIG. 9;
• FIG. 12 is a cross-sectional side view of another possible embodiment of a pumping or mixing system of the present invention;
• FIG. 12ais a cross-sectional view taken alongline12a-12aofFIG. 12;
• FIG. 12bis a cross-sectional view taken alongline12b-12bofFIG. 12;
• FIG. 12cis a cross-sectional view of the embodiment ofFIG. 12, but wherein the motive device is in the form of a winding around the vessel for receiving an electrical current that creates an electrical field and causes the pumping or mixing element to rotate;
• FIG. 13 is an alternate embodiment of an inline levitating pumping or mixing element, similar in some respects to the embodiment ofFIG. 9;
• FIG. 14 is an enlarged partially cross-sectional, partially cutaway side view showing the manner in which a sealed flexible bag carrying a pumping or mixing element may be used for mixing a fluid, and also showing one example of how a transmitter and receiver may be used to ensure that the proper pumping or mixing element is used with the system;
• FIG. 14ais an enlarged, partially cross-sectional, partially cutaway side view showing an attachment including a coupler for coupling with the pumping or mixing element;
• FIG. 14bis an enlarged, partially cross-sectional, partially cutaway side view showing a mixing vessel having centering and alignment structures;
• FIG. 14cis an enlarged, partially cross-sectional, partially cutaway side view showing an alternate orientation of the vessel with centering and alignment structures;
• FIG. 14dis an enlarged, partially cross-sectional, partially cutaway side view showing the use of a second motive device in the system ofFIG. 14, such as a linear motion device, for moving the superconducting element, and hence, the pumping or mixing element to and fro inside of the vessel;
• FIG. 14eis an enlarged, partially cross-sectional, partially cutaway side view showing a mixing vessel having centering and alignment structures;
• FIG. 15 illustrates one charging magnet including a spacer that may form part of a kit for use in charging the superconducting element as it is cooled to the transition temperature, as well as a heater for warning the superconducting element to above the transition temperature for recharging;
• FIG. 16 is as partially cross-sectional, mainly schematic view of an embodiment of the system for use with a vessel having a thin-walled cavity;
• FIG. 16ais a partially cutaway, partially cross-sectional top view of the cryostat ofFIG. 16;
• FIG. 17 is an enlarged, schematic view showing a superconductor or superconducting element comprised of a plurality of segments of a superconducting material having crystallographic planes for levitating a concentric annular levitation magnet, and showing in particular a desired orientation of the crystallographic C-axis of each segment relative to the magnetization vector of the levitation magnet;
• FIG. 18 is a cross-sectional view taken along line18-18 ofFIG. 17;
• FIG. 19 is an embodiment wherein a plurality of superconductors or superconducting elements are used to levitate a pumping or mixing element in a fluid containing vessel, and again showing in particular a desired orientation of the crystallographic C-axis of each segment relative to the magnetization vector of the levitation magnet;
• FIG. 19ais a top view of the cryostat and a portion of the motive device in the system ofFIG. 19;
• FIG. 20 illustrates an embodiment where the cryostat includes a cryocooler which rotates along with the superconducting element to both levitate and rotate the pumping or mixing element in a vessel, which is shown as having a cavity formed therein;
• FIG. 21 is a schematic view showing one possible orientation of the magnets and superconductors in the embodiment ofFIG. 20;
• FIG. 22 illustrates a flexible bag or container having a cavity formed therein, which in addition to receiving the head end of the cryostat may also act as a centering post for a concentric pumping or mixing element; and
• FIG. 23 illustrates an embodiment where permanent magnets are used to provide a levitation-assist function to prevent the pumping or mixing element from contacting the adjacent vessel;
• FIG. 24 is another embodiment where permanent magnets are used to provide a levitation-assist function to prevent the pumping or mixing element from contacting the adjacent vessel;
• FIG. 25 is yet another embodiment where permanent magnets are used to provide a levitation-assist function to prevent the pumping or mixing element from contacting the adjacent vessel;
• FIG. 26 is a partially cross-sectional view showing a vessel including an engagement structure for engaging and supporting the pumping or mixing element when in a non-levitating condition; and
• FIG. 27 is a partially cross-sectional view showing the moving of the cryostat to in turn move the magnetically coupled pumping or mixing element ofFIG. 26 to a levitated position.
DETAILED DESCRIPTION OF THE INVENTION
• Reference is now made toFIG. 1, which shows a first possible embodiment of the mixing or pumpingsystem10 of the present invention. In this embodiment, acryostat12 is used to hold the cooling source for the superconducting element that produces the desired levitation in a pumping or mixingelement14. Thiselement14 is placed in avessel16 positioned external to thecryostat12. Thevessel16 may already contain a fluid F or may be filled after the pumping or mixingelement14 is in place. It should be appreciated at the outset that the term “fluid” is used herein to denote any substance that is capable of flowing, as may include fluid suspensions, gases, gaseous suspensions, or the like, without limitation. Thevessel16 for holding the fluid is shown as being cylindrical in shape and may have an open top. Alternatively, it may be completely sealed from the ambient environment to avoid the potential for fluid contamination or leakage during mixing, or adapted to pump the fluid F from an inlet to an outlet in the vessel16 (seeFIG. 2). In any case, thevessel16 may be fabricated of any material suitable for containing fluids, including glass, plastic, metal, or the like. Of course, the use of lightweight plastic or other high density polymers is particularly desirable if thevessel16 is going to be discarded after mixing or pumping is complete, as set forth in more detail in the description that follows.
• As illustrated inFIG. 1, thevessel16 rests atop theouter wall18 of thecryostat12. Preferably, thisouter wall18 is fabricated of non-magnetic stainless steel, but the use of other materials is of course possible, as long as the ability of the pumping or mixingelement14 to levitate and rotate remains substantially unaffected. Positioned inside of and juxtaposed to thiswall18 is asuperconducting element20. Thesuperconducting element20 is supported by arod22 that serves as the thermal link to acooling source24. Theouter wall18 of thecryostat12 thus defines achamber25 that is preferably evacuated to thermally isolate the coldsuperconducting element20 from the relativelywarm vessel16, pumping or mixingelement14, and fluid F. Positioning of thesuperconducting element20 in thisvacuum chamber25 may be possible by virtue of the thermal link provided by therod22. The thermal isolation and separation provided by thechamber25 allows for thesuperconducting element20 to be placed in very close proximity to theouter wall18 without affecting its temperature, or the temperature of thevessel16. This allows the separation distance from thesuperconducting element20 to the inner surface of thewall18 to be narrowed significantly, such that in the preferred embodiment, the gap G between the two is preferably under 10 millimeters, and can be as narrow as approximately 0.01 millimeters. This substantial reduction in the separation distance enhances the levitational stability, magnetic stiffness, and loading capacity of the pumping or mixingelement14.
• In this first illustrated embodiment, the coolingsource24 is a separate, substantially contained coolingchamber26 holding a cryogen C, such as liquid nitrogen. Thechamber26 is defined by anouter wall28 that is substantially thermally separated from theouter wall18 of thecryostat12 to minimize heat transfer. An inlet I is provided through thiswall28 for introducing the cryogen into the coolingchamber26. To permit any vapor P to escape from thechamber26 as the cryogen C warms, an exhaust outlet O is also provided (see action arrows inFIG. 1 also designating the inlet and outlet). In the illustrated embodiment, the inlet I and outlet O lines may formed of a material having a low thermal conductivity, such as an elongate, thin walled tube formed of non-magnetic stainless steel, and are sealed or welded in place to suspend the coolingchamber26 in thecryostat12. As should be appreciated by one of ordinary skill in the art, the use of a thin walled tube formed of a material having a low thermal conductivity, such as stainless steel, results in a negligible amount of thermal transfer from the inlet or outlet to thewall18. The sealing or welding method employed should allow for thechamber25 to be maintained in an evacuated state, if desired. Despite this illustration of one possible support arrangement, it should be appreciated that the use of any other support arrangement that minimizes thermal transfer between the coolingchamber26 and the cryostat wall orother housing18 is also possible (see. e.g., my '672 patent).
• Therod22 serving as the thermal link between the coolingsource24 and thesuperconducting element20 may be cylindrical and may extend through theouter wall28 of the coolingchamber26. The entire surface area of thesuperconducting element20 should contact the upper surface of thecylindrical rod22 to ensure that thermal transfer is maximized. Therod22 may be formed of materials having low thermal resistance/high thermal conductance, such as brass, copper, or aluminum.
• As should be appreciated from viewingFIG. 1, and as briefly noted in the foregoing description, the combination of theouter wall18 and theinner cooling chamber26 in this first embodiment defines thechamber25 around thesuperconducting element20. Preferably, thischamber25 is evacuated to minimize heat transfer from the coolingchamber walls28 and thesuperconducting element20 to theouter wall18 of thecryostat12. The evacuation pressure is preferably at least 10⁻³torr, and most preferably on the order of 10⁻⁵torr, but of course may vary depending upon the requirements of a particular application. The important factor is that thermal transfer from the coolingsource24, which in this case is the coolingchamber26 holding a cryogen C, and thesuperconducting element20 to theouter wall18 is minimized to avoid cooling thevessel16 or fluid F held therein. Although avacuum chamber25 is proposed as one preferred manner of minimizing this thermal transfer, the use of other means to provide the desired thermal isolation is possible, such as by placing insulating materials or the like in thechamber25.
• As is known in the art, by cooling thesuperconducting element20 in the presence of a magnetic field, it becomes capable of distributing the current induced by a permanent magnet such that the magnet levitates a certain distance above the superconducting element, depending primarily upon the intensity and the direction of the magnetic field generated by the levitating magnet. Although basically a repulsive force is created, the peculiar nature of the pinning forces generated actually tie the levitating magnet to the superconducting element as if the two were connected by an invisible spring. As should be appreciated, this form of attachment cannot be achieved in conventional levitation schemes for pumping or mixing elements that employ two opposed permanent magnets that merely repel each other, since no pinning forces act to tie the two magnets together, while at the same time provide a balancing repulsive force.
• In the preferred embodiment of thepresent system10, theelement20 providing the superconductive effects is a “high temperature” or “type II” superconductor. Most preferably, thesuperconducting element20 is formed of a relatively thin cylindrical pellet of melt-textured Yttrium-Barium Copper Oxide (YBCO) that, upon being cooled to a temperature of approximately 77-78 Kelvin using acooling source24, such as the illustratedliquid nitrogen chamber26, exhibits the desired levitational properties in a permanent magnet. Of course, the use of other known superconducting materials having higher or lower operating temperatures is also possible, and my prior U.S. Pat. No. 5,567,672 is incorporated herein by reference for, among other things, the other high-temperature superconducting materials referenced therein.
• The pumping or mixingelement14 in the preferred embodiment includes a firstpermanent magnet32 for positioning in thevessel16 adjacent to thesuperconducting element20 such that it levitates in the fluid F. Although the polarity of thisfirst magnet32 is not critical to creating the desired levitation, themagnet32 is preferably disk-shaped and polarized in the vertical direction. This ensures that a symmetrical magnetic field is created by themagnet32 and stable levitation results above thesuperconducting element20, while at the same time free rotation relative to the vertical axis is possible.
• In a version of the pumping or mixingelement14 particularly adapted for use in relatively deep fluid vessels, asupport shaft34 is connected to and extends vertically from the firstpermanent magnet32. Along theshaft34, at least one, and preferably two,impellers36 are carried that serve to provide the desired pumping, or in the case ofFIG. 1, mixing action when the pumping or mixingelement14 is rotated. Rotation of the levitating pumping or mixingelement14 in thevessel16 is achieved by a magnetic coupling formed between a second permanent magnet38 (shown in dashed line outline inFIG. 1, but see alsoFIG. 2) and adrive magnet40 positioned externally of thevessel16. Thedrive magnet40 is rotated by a drive means, such as anelectric motor42 or the like, and the magnetic coupling formed with the secondpermanent magnet38 serves to transmit the driving torque to the pumping or mixingelement14 to provide the desired pumping or mixing action. The direction of rotation is indicated by the action arrows shown inFIGS. 1 and 2 as being in the counterclockwise direction, but it should be appreciated that this direction is easily reversed by simply reversing the direction in which thedrive magnet40 is rotated.
• In operation, and in practicing one possible method of pumping or mixing a fluid disclosed herein, thevessel16 containing the fluid F and pumping or mixingelement14 are together placed external to thewall18 of thecryostat12 adjacent to thesuperconducting element20, which is placed in the evacuated or insulatedchamber25. When the first disk-shapedpermanent magnet32 is brought into the proximity of thesuperconducting element20, the symmetrical magnetic field generated causes the entire pumping or mixingelement14 to levitate in a stable fashion above the bottom wall of thevessel16. This levitation brings the secondpermanent magnet38 into engagement with thedrive magnet40 to form the desired magnetic coupling. In addition to transmitting the driving torque, this magnetic coupling also serves to stabilize rotation of the pumping or mixingelement14. Themotor42 or other motive device is then activated to cause thedrive magnet40 to rotate, which in turn induces a steady, stable rotation in the pumping or mixingelement14. Rotatingimpellers36 then serve to mix or pump the fluid F in a gentle, yet thorough fashion.
• Since the pumping or mixingelement14 fully levitates and can be completely submerged in the fluid, the need for mixing or stirring rods penetrating through thevessel16 in any fashion is eliminated. The concomitant need for dynamic shaft seals or support bearings in the vessel walls is also eliminated. Deleterious friction is also not a concern. A related advantage is that thevessel16 containing the fluid F and the pumping or mixingelement14 can be completely sealed from the outside environment before mixing to provide further assurances against leakage or contamination. Yet another related advantage discussed in detail below is that thevessel16 and pumping or mixingelement14 can be formed of relatively inexpensive, disposable materials and simply discarded once mixing is complete. As should be appreciated, this advantageously eliminates the need for cleanup and sterilization of the pumping or mixingelement14 andvessel16. Thus, by completely sealing a disposable vessel, such as a plastic container or flexible bag containing the pumping or mixing element and fluid prior to mixing, the entire assembly can simply be discarded once the fluid contents are recovered. This reduces the risk of exposure both during and after mixing in the case of hazardous fluids, and also serves to protect the fluid from contamination prior to or during the pumping or mixing operation.
• An alternative version of this first possible embodiment of thesystem10 of the present invention particularly adapted for pumping a fluid F is shown inFIG. 2. In this version, thevessel16 includes at least onefluid inlet44 and at least oneoutlet46. The pumping or mixingelement14 preferably carriesrotating impellers36 that serve to provide the desired pumping action by forcing fluid F from theinlet44 to the outlet46 (see action arrows). By increasing or decreasing the rotational speed of themotor42 or other motive device, or adjusting the size, shape or style of the pumping or mixingelement14,impeller blades36, or substituting a different design altogether, a precise level of pumping action may be provided.
• Another possible modification shown inFIG. 2 is to use aclosed cycle refrigerator48 to provide the necessary cooling for thesuperconducting element20 instead of a cryostat with a liquid cryogen as the cooling source. Therefrigerator48 can be positioned externally to ahousing18 containing thesuperconducting element20, which may be the equivalent of the cryostatouter wall18 previously described. As with the first embodiment, achamber25 is defined by thehousing18. Thischamber25 is preferably evacuated or filled with other insulating materials to minimize thermal transfer from thesuperconducting element20 to thehousing18. However, since no coolingsource24 is contained within thehousing18, it is not actually a “cryostat” as that term is commonly defined. Nevertheless, the desired dual levels of thermal separation are still possible, and the concomitant advantages provided, since: (1) thecooling source24,48 is positioned away from thehousing18 and, thus, thevessel16, pumping or mixingelement14, and fluid F; and (2) thehousing18 still separates and defines achamber25 that thermally isolates thesuperconducting element20 and thevessel16. In yet another alternate arrangement, therefrigerator48 can be used as a primary cooling source, with the cryogenic chamber (not shown) serving as a secondary or “backup” cooling source in the event of a power outage or mechanical failure.
• In accordance with another of the many important aspects of thepresent system10, the absence of a mixing rod or other mechanical stirrer extending through a wall of thevessel16 also allows for placement of the pumping or mixingelement14 at an off-axis position, as shown inFIG. 3. Specifically, thesuperconducting element20, pumping or mixingelement14, and drivemagnet40 are all axially aligned away from the vertical center axis of thevessel16. One particular advantage of using this approach is that the pumping or mixingelement14 may be rotated at a very low speed while thevessel16 is also rotated about its center axis. This advantageously ensures that gentle, yet thorough mixing, is achieved, which is particularly advantageous for use with fluids that are sensitive to shear stress. As should be appreciated, this arrangement can be used both whether thevessel16 is completely sealed, provided with aninlet44 and anoutlet46 for pumping as shown inFIG. 2, or open to the ambient environment. For purposes of illustration only,FIG. 3 shows thecryostat12 of the embodiment shown inFIG. 1 having anouter wall18 and acooling chamber26 defined by awall28. However, it should be appreciated that use of thehousing18 and closed-cycle refrigerator48 of the second embodiment ofFIG. 2 as part of the “cryostat” is also possible with this arrangement.
• Through experimentation, it has been discovered that when the pumping or mixingelement14 of the type described for use in this first possible embodiment is employed, providing the requisite degree of stability to ensure that all contact with the side walls of thecontainer16 is avoided may in some instances be a concern. Thus, to ensure that the pumping or mixingelement14 rotates with exceptional stability and such deleterious contact is completely avoided, the secondpermanent magnet38 and thedrive magnet40 are each provided with at least two pairs, and preferably four pairs of cooperating sub-magnets50a,50b.As shown inFIGS. 4aand4b, thesemagnets50a,50bhave opposite polarities and thereby serve to attract each other and prevent the levitating pumping or mixingelement14 from moving from side-to-side to any substantial degree. However, the attractive force is counterbalanced by the combined spring-like attractive and repulsive levitational/pinning forces created between the firstpermanent magnet32 and thesuperconducting element20 when cooled. This avoids the potential for contact with the upper wall of thevessel16, if present. Overall, the pumping or mixingelement14 is capable of exceptionally stable rotation using this arrangement, which further guards against the undesirable frictional heating or shear stress created if the rotating pumping or mixingelement14, or more particularly, the first and secondpermanent magnets32,38 or the blades of theimpellers36 could move into close proximity with the bottom or side walls of thevessel16.
• As should be appreciated, it is possible to rearrange the components of thesystem10 such that the levitation and driving forces are provided from other areas of the vessel, rather than from the top and bottom of the vessel. Thus, as shown inFIG. 4c, thecryostat12 or other housing for containing thesuperconducting element20 may be positioned adjacent to one side of thevessel16, while thedrive magnet40 is positioned adjacent to the opposite side. In that case, the pumping or mixingelement14 may be turned on its side and supported by a separate stable support structure, such as a table T or the like. Thevessel14 is shown as being sealed, but it should be appreciated that any of the vessels disclosed herein may be employed instead, including even a straight or L-shaped pipe.
• To assist in levitating the pumping or mixingelement14 in either the embodiment ofFIG. 1 or2 or the other embodiments disclosed herein, at least one, and preferably a plurality ofchambers60 are provided for containing a substance lighter than the surrounding fluid F. Thechambers60 may be provided adjacent to eachmagnet32,38 in the pumping or mixingelement14, as well as around theshaft34, if desired. In the preferred embodiment where the fluid F is or has a specific gravity similar to that of water, the substance contained in thechambers60 may be air. However, in more viscous fluids, such as those having a specific gravity more like glycerin, it may be possible to use lighter fluids, such as water, even lighter gases, or combinations thereof. Thesechambers60 thus serve to assist in levitating the pumping or mixingelement14 by helping it “float” in the fluid F. However, the “pinning” force created by thesuperconducting element20, plus the levitating and aligning force created between the secondpermanent magnet38 and the drivingmagnet40, both also serve to assist in keeping the pumping or mixingelement14 in the proper position as it rotates. In the case of disk or pancake shaped permanent first andsecond magnets32,38 and acylindrical shaft34,annular chambers60 may be used. Instead of fluid or gas filled chambers, the use of other buoyant materials is also possible to provide the levitation-assist function.
• As previously mentioned, one of the many advantages of thesystem10 of the present invention is that, since the pumping or mixingelement14 levitates in the fluid F and no mixing or stirring rods are required for rotation, thevessel16 can be completely sealed from the outside ambient environment. Thus, by forming the pumping or mixingelement14 andvessel16 of relatively inexpensive or disposable materials, both can simply be discarded after mixing is completed and the fluid F is recovered. Of course, such disposable materials can also be used to form thevessel16 designed for pumping fluids (FIG. 2), or to form the open-top container for mixing fluids to avoid the need for clean up or sterilization once the operation is complete.
• It should also be appreciated that the pumping or mixingelement14 illustrated is an example of one preferred arrangement only, and that other possible configurations are possible. For instance, impeller blades are not required, since a smooth-walled, disk-shaped pumping or mixing element alone creates some gentle mixing action simply by rotating. If present, the blade or blades could simply be placed circumferentially around the disk-shaped firstpermanent magnet32 to reduce the length of theshaft34, or eliminate it altogether, especially if thevessel16 has a relatively small vertical dimension. Instead of abladed impeller assembly36, the use of other structural arrangements is also possible, such as disk-shaped wheels having vanes or like structures designed to create more or less efficient rotation, and a concomitant increase in the desired mixing or pumping action when rotated. Depending on the depth of thevessel16, the length of theshaft34, if present, can also be increased or decreased as necessary. All components forming the pumping or mixing element in any embodiment described above may be coated with TEFLON or other inert materials to reduce the chances of contamination or corrosion, as well as to facilitate clean up, if required.
• Of course, besides use in the mixing or pumping of small batches of fluid solutions or suspensions used during experimentation and research in the laboratory setting, all components are also easily scaled up for use in industrial or commercial pumping or mixing operation, such as those commonly used in the manufacture of large batches pharmaceuticals or food products. The stable, reliable levitation of the magnetic pumping or mixing element can still be readily achieved in systems of much greater capacity than the one shown for purposes of illustration in the drawings, thus making the present arrangement particularly well-suited for the commercial production of pharmaceuticals or any other solutions or suspensions that require gentle, yet thorough mixing during processing.
• Experiments conducted to date have demonstrated the efficacy of thesystem10 described above. The set-up utilized in conducting these experiments included a pumping or mixing element having axially aligned upper and lower magnets and an impeller assembly mounted on a vertically extending support shaft, as shown inFIG. 1. A cylindrical pellet of melt-textured YBa₂Cu₃O_7+xhaving a diameter of 30 millimeters and a thickness of 25 millimeters was used as the superconducting element and placed in a cryostat having a configuration similar to the one shown inFIG. 1. The cryostat included a cooling chamber filled with approximately 1 liter of liquid nitrogen. A Nd—Fe—B permanent magnet with a surface field intensity of 0.4 Tesla was used as the lower, first permanent magnet.
• Using this set-up, the experiments demonstrated that the desired exceptionally stable levitation of the pumping or mixing element above the top surface of the cryostat in a vessel filled with a relatively warm fluid was possible. A separation distance of up to seven millimeters was achieved, and the levitation was stable for up to five hours using just a liter of liquid nitrogen as the cryogen. In the first experiment using this set up, water was selected as a model low viscosity fluid. Rotational speeds of up to 600 rpm were achieved—this upper limit being defined by only the limited capabilities of the motor used to rotate the drive magnet in this experiment. No decoupling or instability in the pumping or mixing element was observed at any speed. In the case of glycerin, a model high viscosity fluid, a maximum rotational speed of 60 rpm was achieved before some decoupling of the pumping or mixing element was observed. To further demonstrate the mixing capabilities using the proposed system, SEPHADEX powder (dry bead, 50-150 micron diameter) was placed on the bottom of a water-filled vessel and the levitating pumping or mixing element rotated. A uniform suspension was achieved after approximately five minutes of mixing.
• As should be appreciated, thesystem10 described above and shown inFIGS. 1-4 is based on the use of a stationarysuperconducting element20 and a pumping or mixingelement14 that, in addition to a “levitation” magnet, includes one or more separate driven magnets for coupling with a drive mechanism, such as one positioned at the opposite end of the vessel or container relative to the superconducting element. However, other embodiments of the pumping or mixing system may include a levitating, rotating pumping or mixing element with magnets that are simultaneously used not only for levitation, but also for transmitting driving torque. In one embodiment, this driving torque is simultaneously provided by the pinning forces that couple the pumping or mixing element with a rotating superconducting element. Thus, the superconducting element causes the pumping or mixing element to both levitate and rotate, even though there is no physical contact between the two elements.
• More specifically, and in accordance with this second possible embodiment of the present invention illustrated inFIG. 5, the pumping or mixingsystem100 includes acryostat102, which may be formed of two separate components: afirst component102aincluding anouter wall104 that surrounds a relatively thin, disk-shapedsuperconducting element106 to define achamber108, and a second component102bincluding thecooling source110. Preferably, theouter wall104 is formed of thin, non-magnetic material, such as non-magnetic stainless steel or the like, but the use of other materials is possible, as long as they do not interfere with the operation of thesystem100 and have relatively poor thermal conductivity. Thechamber108 surrounding thesuperconducting element106 may be evacuated or insulated as described above to thermally isolate and separate it from thewall104. However, in this embodiment, and as noted further below, it is possible to eliminate thechamber108 entirely in the case where a non-temperature sensitive fluid is being pumped or mixed.
• In the case where thechamber108 is evacuated, avalve112 may be provided in theouter wall104 for coupling to a vacuum source. An optional getter114 (such as an activated carbon insert or the like) may be positioned in thechamber108 for absorbing any residual gases and ensuring that the desired evacuation pressure is maintained. As with the embodiments described above, the evacuation pressure is preferably on the order of 10⁻³torr or greater, but may vary depending on the particular application.
• Thesuperconducting element106 is supported in thechamber108 independent of theouter wall104 of thefirst portion102aof thecryostat102. The support may be provided by aplatform116 that is enclosed bywall104 and supported at one end of an elongatedthermal link118, preferably formed of metal or another material having a high degree of thermal conductivity (e.g., 50 Watts/Kelvin or higher). To supply the necessary cooling to the superconducting element, the opposite end of the elongatedthermal link118 is positioned in contact with thecooling source110, which as described above forms a part of the second component102bof the “cryostat”102 (the term cryostat being used throughout to denote a structure or combination of structures that are capable of maintaining a superconducting element in a cold state, whether forming a single unit or not). Thecooling source110 is illustrated schematically as an open-top container119, such as a Dewar flask, containing a liquid cryogen C, such as nitrogen. However, it is also possible to use a closed-cycle refrigerator or any other device capable of supplying the cooling necessary to levitate a magnet above a superconducting element after field cooling is complete. In the case where thewall104 of thefirst portion102aof thecryostat102 makes contact with the cryogenic fluid C, as illustrated, it should be appreciated that there is only negligible thermal transfer to the portion of thewall104 adjacent the vessel, since: (1) thewall104 may be formed of a thin material having low thermal conductivity; and (2) the portion of thewall104 adjacent to the vessel is surrounded by the ambient, room-temperature environment.
• To permit thesuperconducting element106 to rotate, aroller bearing assembly120 comprising one or moreannular roller bearings122 supports the first portion of thecryostat102a, including thewall104 defining thechamber108. As should be appreciated from viewingFIG. 5, theseroller bearings122 permit the first portion of thecryostat102ahousing thesuperconducting element102 to rotate about an axis, which is defined as the axis of rotation. A bearinghousing124 or the like structure for supporting the bearing(s)122 is secured to an adjacentstable support structure126. In the illustrated embodiment, a motive device includes anendless belt128 that serves to transmit rotational motion from the pulley129 keyed or attached to the shaft130 of amotor131 to the first portion of thecryostat102a.Themotor131 may be a variable speed, reversible electric motor, but the use of other types of motors to create the rotary motion necessary to cause thesuperconducting element106, and more particularly, the first portion of thecryostat102ahousing thesuperconducting element106, to rotate is possible.
• Thevessel132 containing the fluid to be mixed (which as described below can also be in the form of a centrifugal pumping head for transmitting a fluid) is positioned adjacent to the rotatingsuperconducting element106, preferably on a stable support surface T fabricated of a material that does not interfere with the magnetic field created by the pumping or mixingelement134. As previously noted, thevessel132 can be a rigid vessel of any shape (open top, sealed having an inlet or outlet, cylindrical with a hollow center, such as a pipe, or even a flexible plastic bag (by itself, with rigid inserts, or inserted into a rigid or semi-rigid vessel)). The only requirement is that thevessel132 employed is capable of at least temporarily holding the fluid F (or gas) being mixed or pumped.
• To create the desired mixing action in this embodiment, a pumping or mixingelement134 is positioned in thevessel132 and simultaneously levitated and rotated by thesuperconducting element106. More specifically, the first portion of thecryostat102acontaining thesuperconducting element106,thermal link118, and the evacuatedchamber108 is rotated as a result of the rotational motion transmitted by theendless belt128. This rotation causes the pumping or mixingelement134 in thevessel124 to rotate and either pump or mix the fluid F held therein. In the case where thechamber104 is evacuated or insulated, the pumping or mixingelement134 is rotated in a stable, reliable fashion while the desired thermal separation between the coldsuperconducting element106 supplying the levitation force, thevessel124, and hence the fluid F, is achieved. The pumping or mixingelement134 may include a plurality of mixing blades B (seeFIGS. 6aand6b), vanes V (not shown, but seeFIG. 7), or like structures to create an impeller. However, again referring back toFIG. 5, a low-profile, disk-shaped pumping or mixingelement134 may also be used to provide the desired mixing action, especially for particularly delicate fluids, such as blood or other types of cell suspensions.
• As perhaps best understood by viewingFIGS. 6aand6btogether, the pumping or mixingelement134 may include at least twomagnets135a,135b,and possibly more than two (seeFIG. 20). Thesemagnets135a,135bnot only serve to generate the magnetic field that causes the pumping or mixingelement134 to levitate above thesuperconducting element106, but also transmit rotational motion to the pumping or mixing element. As should be appreciated by one of ordinary skill in the art, the magnetic field generated by themagnets135a,135bshould be axially non-symmetrical relative to the axis of rotation of thesuperconducting element106 in order to create the magnetic coupling necessary to efficiently transmit the rotary motion. In one embodiment, themagnets135a,135bare disk-shaped and polarized along a center vertical axis (seeFIG. 6b, showingpermanent magnets135a,135bof alternating polarities (N-North; S-South) levitating above a pair ofsuperconducting elements106a,106b,with the corresponding action arrows denoting the direction and axis of polarity). Thesemagnets135a,135bcan be fabricated from a variety of known materials exhibiting permanent magnetic properties, including, but not limited to, Neodymium-Iron-Boron (NdFeB), Samarium Cobalt (SMCo), the composition of aluminum, nickel, and cobalt (Alnico), ceramics, or combinations thereof Themagnets135a,135bmay be interconnected by a piece of an inert matrix material M, such as plastic or inert, non-corrosive metals. Alternatively, themagnets135a,135bmay each be embedded in separate pieces of a matrix material M, or may be embedded in a single unitary piece of material (not shown). Also, as previously mentioned, the pumping or mixingelement134 may carry one or more optional blades B, vanes or like structures to enhance the degree of pumping or mixing action created.
• In another possible embodiment, the second portion of the cryostat102bincluding the cooling source (either a liquid cryogen container (open top, sealed with inlet/outlet ports, or a refrigerator (preferably a “cryocooler,” as described further below)) may be rigidly attached to thefirst portion102aand both components may be simultaneously rotated together (see the dashed lines at the top of theopen cooling container119 inFIG. 5, and see also the embodiment described below and shown inFIGS. 20-21). The rotational motion may be supplied by an endless belt/motor combination, as described above, or alternatively may be provided through a direct coupling between the second portion of the cryostat102b(comprising any type of cooling source) and an inline shaft extending from or coupled to a motor or similar motive device (not shown).
• As briefly mentioned above, it is possible to use this embodiment of thesystem100 without evacuating, insulating, or otherwise thermally separating thesuperconducting element106 from the ambient environment, such as for mixing or pumping cold (cryogenic) or non-temperature sensitive fluids. In that case, there is no specific need for awall104 orchamber108 surrounding thesuperconducting element106, since thermally separating it from the structure supporting the vessel132 (e.g., a table, stand or the like) is unnecessary. Even with this modification, reliable and stable levitation of the pumping or mixingelement134 is still achieved.
• From the foregoing, it should be appreciated that the same driving mechanism and cryostat shown inFIG. 5 can be used for pumping a fluid instead of mixing it. One version of avessel132 in the form of acentrifugal pumping head150 is shown inFIG. 7. This pumpinghead150 includes apumping chamber152 having aninlet154 and an outlet156 (which of course, could be reversed, such as in a non-centrifugal pumping head (seeFIG. 2)). Thechamber150 contains the levitating pumping or mixingelement158, which as shown may include a plurality of vanes V, or may alternatively carry a plurality of blades (not shown). At least two permanent magnets160a,160bhaving different polarities are embedded or otherwise included in the pumping or mixingelement158, which may be substantially comprised of an inert matrix material M having any desired shape to facilitate the pumping or mixing action. As described above, these magnets160a,160bprovide both levitation and torque transmission as a result of the adjacent rotatingsuperconducting element106.
• As should be appreciated, one advantage of providing the driving force for the levitating pumping or mixingelement158 from the same side of the vessel/pumping head150 from which the levitating force originates is that the fluid inlet154 (oroutlet156, in the case where the two are reversed) may be placed at any location along the opposite side of the vessel/pumping head150, including even the center, without interfering with the pumping or mixing operation. Also, this same side of the vessel/pumping head150 may be frusto-conical or otherwise project outwardly, as illustrated, without interfering with the rotation or necessitating a change in the design of the pumping or mixingelement134,158.
• As briefly noted above, in some instances the opening in a vessel may be too small to permit an even moderately sized pumping or mixingelement134 to be inserted into the fluid F. In such a case, alternate versions of a pumping or mixingelement134 meeting this particular need are shown inFIGS. 8a-8c.In the first alternate version, the pumping or mixingelement134ais in the form of a slender rod formed of an inert matrix material M carrying one of the levitating/drivenmagnets135a,135bat or near each end. As should be appreciated, this pumping or mixingelement134amay be easily turned to an upstanding position and inserted in the opening. Upon then coming into engagement with the rotatingsuperconducting element106, the pumping or mixingelement134awould simultaneously levitate and rotate to pump or mix a fluid held in the vessel. To further facilitate insertion in the narrow opening, the matrix material M may be an elastomeric material or another material having the ability to freely flex or bend.
• A second version of a pumping or mixingelement134bfor use with a vessel having a narrow opening is shown inFIG. 8b. The pumping or mixingelement134bincludes first and secondthin rods180 formed of a matrix material M. Therods180 each carry the levitating/drivenmagnets135a,135bat each end thereof, with at least two magnets having the identical polarity being held on each different rod. In one version, therods180 are pinned about their centers (note connecting pin182) and are thus capable of folding in a scissor-like fashion. As should be appreciated fromFIG. 8c, this allows the pumping or mixingelement134bto be folded to a low-profile position for passing through the opening of thevessel132. Therods180 of the pumping or mixingelement134bmay then separate upon coming into engagement with an appropriately field cooledsuperconducting element106 positioned adjacent to the bottom of thevessel132. Sincemagnets135aor135hhaving the same polarity are positioned adjacent to each other, the corresponding ends of therods180 repel each other as the pumping or mixing element132brotates. This prevents therods180 from assuming an aligned position once in thevessel132. As should be appreciated, instead of pinning twoseparate rods180 together to form the pumping or mixingelement134b,it is also possible to integrally mold therods180 of a flexible material to form a cross. This would permit therods180 of the pumping or mixing element134hto flex for passing through any narrow opening, but then snap-back to the desired configuration for levitating above thesuperconducting element106.
• In accordance with yet another aspect of the present invention, a third version of a pumping or mixingsystem200 is disclosed. In this third embodiment, which is illustrated inFIGS. 9,9a,9b, and10, the forces for driving and levitating the pumping or mixingelement204 are supplied from the same side of a fluid vessel202 (which is shown as an open-top container, but as described above, could be a sealed container, a pumping chamber or head, a flexible bag, a pipe, or the like). In thissystem200, the pumping or mixingelement204 actually includes two magnetic subsystems: a first one that serves to levitate the pumping or mixingelement204, which includes afirst magnet206, preferably in the form of a ring, and a second magnetic subsystem that includes at least two alternating polarity drivenmagnets208a,208b,preferably positioned inside of the first, ring-shapedmagnet206, to transmit driving torque to the pumping or mixing element (seeFIGS. 9aand9b).
• FIG. 9 shows one embodiment of theoverall system200 in which the ring-shapedpermanent magnet206 or array of magnets (not shown) provides the levitation for the pumping or mixingelement204. Polarization of thering magnet206 is vertical (as shown by the long vertical arrows inFIG. 9b). The drivenmagnets208a,208bare shown as being disk-shaped and having opposite or alternating polarities (see corresponding short action arrows inFIG. 9brepresenting the opposite polarities) to form a magnetic coupling and transmit the torque to the levitating pumping or mixingelement204.Levitation magnet206 and drivenmagnets208a,208bare preferably integrated in one rigid structure such as by embedding or attaching all three to a lightweight, inert matrix material M, such as plastic or the like.
• To correspond to the ring-shaped levitation magnet, thesuperconducting element210 for use in this embodiment is annular, as well. Thiselement210 can be fabricated of a single unitary piece of a high-temperature superconducting material (YBCO or the like), or may be comprised of a plurality of component parts or segments. Upon being cooled to the transition temperature in the presence of a magnetic field and aligning with the ring-shapedpermanent magnet206 producing the same magnetic field, thesuperconducting ring210 thus provides the combined repulsive/attractive, spring-like pinning force that levitates the pumping or mixingelement204 in thevessel202 in an exceptionally stable and reliable fashion. InFIG. 9, the vessel is shown as being supported on the outer surface of aspecial cryostat220 designed for use with thissystem200, a detailed explanation of which is provided in the description that follows. However, it is within the broadest aspects of the invention to simply support thevessel202 on any stable support structure, such as a table (not shown), as long as it remains sufficiently close to thesuperconducting element210 to induce the desired levitation in the pumping or mixingelement204 held therein.
• As in the embodiments described above, a motive device is used to impart rotary motion to the pumping or mixingelement204, and is preferably positioned adjacent to and concentric with the annularsuperconducting element210. One example of a motive device for use in thesystem200 of this third embodiment includes drivingmagnets212a,212bthat correspond to the drivenmagnets208a,208bon the pumping or mixingelement204 and have opposite polarities to create a magnetic coupling (seeFIG. 9b). The drivingmagnets212a,212bare preferably coupled to ashaft214 also forming part of the motive device. The drivingmagnets212a,212bmay be attached directly to theshaft214, or as illustrated inFIG. 9, may be embedded or attached to a matrix material (not numbered inFIG. 9, but seeFIG. 9b). By positioning the drivingmagnets212a,212bclose to the pumping or mixingelement204, such as by inserting them in the opening or bore219 defined by the annularsuperconducting element210, and rotating theshaft214 using amotor216 also forming a part of the motive device, synchronous rotation of the levitating pumping or mixingelement204 is induced. The pumping or mixingelement204 may include one or more blades B that are rigidly attached to the ring or levitation magnet206 (or any matrix material forming the periphery of the pumping or mixing element204). However, it remains within the broadest aspects of the invention to simply use a smooth, low-profile pumping or mixing element (seeFIG. 5) to provide the desired mixing action.
• As shown inFIGS. 9 and 10 and briefly mentioned above, the mixing orpumping system200 including the pumping or mixingelement204 comprised of themagnetic levitation ring206 and separate drivenmagnets208a,208bmay use aspecial cryostat220 to ensure that reliable and stable rotation/levitation is achieved. As perhaps best shown in the cross-sectional side view ofFIG. 9, thecryostat220 includes acooling source221 for indirectly supplying the necessary cooling to thesuperconducting element210, which as described below is supported and contained in a separate portion of thespecial cryostat220. In the illustrated embodiment, the cooling source221 (not necessarily shown to scale inFIG. 9) includes acontainer222, such as a double-walled Dewar flask, in which afirst chamber224 containing a liquid cryogen C (nitrogen) is suspended. Asecond chamber223 defined around thefirst chamber224 is preferably evacuated or insulated to minimize thermal transfer to the ambient environment, which is normally at room temperature. Aport226 is also provided for filling the suspendedchamber224 with the chosen liquid cryogen C, as well as for possibly allowing any exhaust gases to escape. As with the first and second embodiments described above, thecooling source221 may instead take the form of a closed-cycle refrigerator (not shown), in which case thedouble wall container222 may be entirely eliminated from thesystem200.
• Athermal link228 is provided between the cooling source (in the illustrated embodiment, the container222) and aplatform230 suspended in thecryostat220 for supporting thesuperconducting ring210. The use of theplatform230 is desirable to ensure that the temperature of thesuperconducting element210 is kept below the transition temperature, which in the case of a “high temperature” superconducting material (such as YBCO) is most preferably in the range of between 87-93 Kelvin. However, the use of theplatform230 is not critical to the invention or required as part of thespecial cryostat220, since thethermal link228 could extend directly to thesuperconducting element210. Thethermal link228 may be a solid rod of material, including copper, brass, or any other material having a relatively high thermal conductivity. Instead of a solid rod, it is also possible to provide anopen channel232 in thethermal link228, especially when a liquid cryogen C capable of flowing freely, such as nitrogen, is used as thecooling source221. Thischannel232 allows the cryogen C from the suspendedcontainer224 to reach theplatform230 directly. Of course, the direct contact with the cryogen C may provide more efficient and effective cooling for thesuperconducting element210, but is not required.
• The ring-shapedplatform230 that supports the superconducting element(s)210 and supplies the desired cooling via thermal conduction may be made of copper, brass, aluminum, or another material having good thermal conductivity. It may be in the form of a solid ring, as illustrated, or may be in the form of a hollow ring (such as a substantially circular or elliptical torus, not shown). This would allow the liquid cryogen C to flow completely around the ring to further increase the efficiency with which the cooling is transferred to thesuperconducting element210. In any case, where aplatform230 is used, care should be taken to ensure that full contact is made with at least a majority of the corresponding surface of thesuperconducting element210, since even cooling helps to ensure that the desired smooth, even, and reliable levitation is achieved.
• To reduce the thermal transfer to thevessel202 in the case where a temperature sensitive fluid is being pumped or mixed by thesystem200, a ring-shaped wall orenclosure234 surrounding theplatform230 and the annularsuperconducting element210 defines afirst chamber235. In addition, a hollow cylindrical wall orenclosure236 may also surround thethermal link232 and define asecond chamber237. Preferably, these first andsecond chambers235,237 are evacuated or insulated to minimize thermal transfer between the ambient environment and the cold elements held therein. In a preferred embodiment, eachenclosure234,236 is fabricated from non-magnetic stainless steel, but the use of other materials is of course possible, as long as no interference is created with the levitation of the pumping or mixingelement204. As with the second embodiment described above, it is also possible to use thesystem200 of the third embodiment to pump or mix cryogenic or non-temperature sensitive fluids, in which case there is no need to evacuate or insulate theenclosures234,236, or to even use thespecial cryostat220 described herein.
• As should be appreciated, it is possible to create thechambers235,237 defined by theenclosures234,236 and thechamber223 such that all three are in fluid communication and thus represent one integrated vacuum space (not shown). This facilitates set-up, since all threechambers223,235,237 may be evacuated in a single operation, such as by using a vacuum source coupled to a single valve (not shown) provided in one of the chambers. However, separately evacuating eachchamber223,235,237 is of course entirely possible. Also, instead of or in addition to evacuating thechambers223,235,237, some or all may be instead filled with a suitable insulating material (not shown).
• As should be appreciated, to rotate the pumping or mixingelement204 in this embodiment, it is desirable to place thedrive magnets212a,212bin close proximity to the pumping or mixing element, but preferably on the same side of thevessel202 as thesuperconducting element210. Accordingly, thespecial cryostat220, and more specifically, the wall orenclosure234 defines a room-temperature cylindrical bore or opening240 that allows for the introduction of the end of theshaft214 carrying the drivingmagnets212a,212b,which are at room temperature. As a result of this arrangement, theshaft214, which is part of the motive device, is concentric with thesuperconducting element210. Theshaft214 is also positioned such that the drivingmagnets212a,212balign with the drivenmagnets208a,208bon the pumping or mixingelement204 when the levitatingmagnet206 is aligned with thesuperconducting element210. Thus, despite being positioned adjacent to and concentric with thesuperconducting element210, theshaft214 and drivingmagnets212a,212bremain at room temperature, as does thevessel202, the fluid F, and the pumping or mixingelement204.
• An example of one possible embodiment of acentrifugal pumping head250 for use with thesystem200 ofFIG. 9 is shown inFIG. 11. Thehead250 includes a levitating pumping or mixingelement252 that carries one or more optional blades or vanes V (which are upstanding in the side view ofFIG. 11), a fluid inlet254 (which as should be appreciated can be in the center at one side of thepumping head250 in view of the fact that the levitation and driving forces are both supplied from the same side of the vessel202), afluid outlet256, drivenmagnets258a,258b,and a ring-shapedlevitation magnet260.
• In yet another possible embodiment of the invention, as shown in the cross-sectional view ofFIG. 12, thesystem300 includes a pumping or mixingelement302 adapted for inline use, such as when the vessel is in the form of ahollow pipe304. The pumping or mixingelement302 includes first and second spaced levitatingmagnets305a,305b,one of which is preferably positioned at each end to ensure that stable levitation is achieved. Themagnets305a,305bpreferably correspond in shape to the vessel, which in the case of apipe304, means that they are annular. Themagnets305a,305bare carried on ashaft306 forming a part of the pumping or mixingelement302, which further includes a drivenmagnet308. The drivenmagnet308 may be comprised of a plurality of sub-magnets308a. . .308nhaving different polarities and arranged in an annular configuration to correspond to the shape of thepipe304 serving as the vessel in this embodiment (seeFIG. 12b). All threemagnets305a,305b,and308 may be embedded or attached to an inert matrix material M, such as plastic, that provides the connection with theshaft306. Theshaft306 of thebearing302 may also carry one or more blades B.
• First and second “cryostats”310a,310bare also provided. As perhaps best understood with reference to the cross-sectional view ofFIG. 12a, the first “cryostat”310aincludes a superconductor for levitating the pumping or mixing element in the form of an annularsuperconducting element312a.Thissuperconducting element312ais suspended in achamber314adefined by thecryostat310a,which may be evacuated or insulated to prevent thermal transfer to thepipe304 or the passing fluid F. Thecryostat310amay include an inner wall adjacent to the outer surface of the pipe304 (not shown), but such a wall is not necessary in view of the thermal separation afforded by the evacuated or insulated space surrounding thesuperconducting element312a.Thesuperconducting element312amay be coupled toannular support platform316a,which in turn is thermally linked to one or moreseparate cooling sources318. The connection is only shown schematically inFIG. 12, but as should be appreciated from reviewing the foregoing disclosure, may include a rod that serves to thermally link a container holding a liquid cryogen or a closed cycle refrigerator to thesuperconducting element312a.While not shown in detail. “cryostat”310bmay be similar or identical to thecryostat310ajust described.
• With reference now toFIGS. 12band12c, two different motive devices for rotating the pumping or mixingelement302 in thepipe304 are disclosed. The first motive device includes a drivingmagnet assembly320 that is rotatably supported on abearing322, such as a mechanical ball or roller bearing, carried on the outer surface of thepipe304. Themagnet assembly320 includes a plurality of drivingmagnets320a. . .320n,also having different or alternating polarities. As with the drivenmagnets308a. . .308n,the drivingmagnets320a. . .320nare embedded or attached to an inert, non-magnetic matrix material M, such as plastic. Anendless belt324 also forming a part of the motive device frictionally engages both the drivingmagnet assembly320 and a pulley or wheel W earned on the spindle or shaft of a motor (preferably a reversible, variable speed electric motor, as described above).
• As should now be appreciated, the pumping or mixingelement302 is caused to levitate in thepipe304 as a result of the interaction of thelevitation magnets305a,305bwith the adjacentsuperconducting elements310a,310b,which may be thermally separated from the outer surface of the pipe304 (or the adjacent inner wall of thecryostat310a,310b,if present). Upon then rotating themagnetic drive assembly320, the pumping or mixingelement302 is caused to rotate in thepipe304 serving as the vessel to provide the desiring pumping or mixing action. Even if the fluid F is flowing past the pumping or mixingelement302, it remains held in place in the desired position in thepipe304 as a result of the pinning forces created by thesuperconducting elements310a,310bacting on thelevitation magnets305a,305b.
• The second version of a motive device is shown in the cross-sectional view ofFIG. 12c, which is similar to the cross-section taken inFIG. 12b. However, instead of amagnetic driving assembly320,endless belt324, and motor, rotary motion is imparted to the pumping or mixingelement302 by creating an electrical field around thepipe304. This may be done by placing a winding326 around the outer wall of thepipe304 and supplying it with an electrical current, such as from apower supply328 or other source of AC current. Since the pumping or mixingelement302 carriesmagnets308a. . .308nhaving different polarities, the resulting electric field will thus cause it to rotate.
• Yet another embodiment of an inline pumping or mixing system400 is shown inFIG. 13. Thecryostat402 in this case is essentially positioned directly in the path of fluid flow along thepipe403, thus creating an annular (or possibly upper and lower) flow channels404a,404b.Thecryostat402 has anouter wall406 that defines achamber408 for containing asuperconducting element410. Thesuperconducting element410 may be annular in shape, in which case thechamber408 is of a similar shape. Thechamber408 may also be evacuated or insulated to thermally separate thesuperconducting element410 from theouter wall406. Thesuperconducting element410 is thermally linked to aseparate cooling source412, with both the thermal link and the cooling source being shown schematically inFIG. 13. It should be appreciated that thiscryostat402 is similar in many respects to the one described above in discussing the third embodiment illustrated inFIG. 9, which employs a similar, but somewhat reoriented, arrangement.
• Thewall406 creatingannular chamber408 for thesuperconducting element410 defines a room temperature bore or opening414 into which a portion of a motive device may be inserted, such as the end of ashaft416 carrying at least two driving magnets.FIG. 13 illustrates the motive device with three such drivingmagnets418a,418b,418c,one of which is aligned with the rotational axis of theshaft416. The opposite end of theshaft416 is coupled to a motor (not numbered), which rotates the shaft and, hence, the drivingmagnets418a,418b,and418c.Themagnets418a,418b,418cmay be coupled directly to theshaft416, or embedded/attached to an inert matrix material M.
• The pumping or mixingelement420 is positioned in thepipe403 adjacent to theouter wall406 of thecryostat402. The pumping or mixingelement420 includes alevitation magnet422 that corresponds in size and shape to thesuperconducting element410, as well as drivenmagnets424a,424b,424cthat correspond to the drivingmagnets418a,418b,and418c.Thelevitation magnet422 and driven magnets424a-424care attached to or embedded in a matrix material M, which may also support one or more blades B that provide the desired pumping or mixing action.
• In operation, the motor rotates theshaft416 to transmit rotary motion to the drivingmagnets418a,418band418c.As a result of the magnetic coupling formed between these magnets418a-cand the opposite polarity driven magnets424a-c, the pumping or mixingelement420 is caused to rotate in the fluid F. At the same time, the pumping or mixingelement420 remains magnetically suspended in the fluid F as the result of the pinning forces created between thesuperconducting element410 and thelevitation magnet422. The operation is substantially the same as that described above with regard to the third embodiment, and thus will not be explained further here.
• Various optional modifications may in some circumstances enhance the set-up or performance of any of the systems described herein, or instead adapt them for a particular use, purpose, or application. As noted previously, the disposable vessel or container for holding the fluid undergoing pumping or mixing may be in the form of a flexible bag. An example of such abag500 is shown inFIG. 14, along with thesystem100 for levitating the pumping or mixingelement502 ofFIG. 5. Thebag500 may be sealed with either fluid F or the pumping or mixing element502 (which may take the form of one of the several pumping or mixing elements disclosed above or an equivalent thereof) inside prior to distribution for use, or may be provided with a sealable (or resealable) opening that allows for the fluid and pumping or mixing element to be introduced and later retrieved.
• Both the pumping or mixingelement502 andbag500, whether permanently sealed or resealable, may be fabricated of inexpensive, disposable materials. Accordingly, both can simply be discarded after the pumping or mixing operation is completed and the fluid F is retrieved. It should also be appreciated that the vertical dimension of thebag500 is defined by the volume of fluid F held therein. Thus, instead of placing thebag500 containing the pumping or mixingelement502 directly on the surface of the cryostat, table T, or other support structure adjacent to thesuperconducting element106, it is possible to place theflexible bag500 in a separate rigid or semi-rigid container (see, e.g.,FIG. 22). This helps to ensure that the fluid F provides thebag500 with a sufficient vertical dimension to permit the pumping or mixingelement502 to freely rotate in a non-contact fashion. Alternatively, thebag500 may include internal or external reinforcements (not shown) to enhance its rigidity without interfering with the rotation of the pumping or mixing element.
• In cases where the pumping or mixingelement502 is prepackaged in thebag500, with or without fluid, it may inadvertently couple to adjacent magnets or other metallic structures. Breaking this coupling may render the bag susceptible to puncturing, tearing, or other forms of damage. Accordingly, as shown inFIGS. 14aand14b, it may be desirable to hold the pumping or mixingelement502 place prior to use with any of the systems described herein, especially in cases where it is sealed inside the vessel/bag500 during manufacturing
• As shown inFIG. 14a, one manner of holding theelement502 in place is to use anattachment520, cover, or similar device including acoupler522 formed of a ferromagnetic material or the like adjacent to thebag500. Thiscoupler522 is thus attracted to and forms a magnetic coupling with the pumping or mixingelement502 when theattachment520 is in place. As a result of this coupling, the pumping or mixingelement502 is prevented from coupling with magnets in adjacent bags or other magnetic structures (not shown). Theattachment520 should be fabricated of a non-magnetic material, such as rubber. In the operative position, thecoupler522 shields the magnetic field created by the pumping or mixingelement502. When the assembly including thebag500 and the pumping or mixingelement502 is ready for use, theattachment520 may simply be removed from thebag500 to break the magnetic coupling between the pumping or mixingelement502 and thecoupler522.
• A second manner of keeping the pumping or mixingelement502 at a desired location to facilitate coupling with the particular levitation/rotation devices used is to provide thebag500 with a “centering” structure, such as apost528. As shown in the embodiment illustrated inFIG. 14b, which includes the basic levitation and rotation system ofFIG. 5, thispost528 may take the form of a rigid or semi-rigid piece of material projecting into the interior of thebag500. Preferably, thepost528 is formed of the same material as thebag500 or other container (plastic) and has an outer diameter that is less than the inner diameter or a bore or opening formed in the pumping or mixingelement502. As should be appreciated, the pumping or mixingelement502 may be held in place on thepost528 by gravity during shipping, prior to use, and even between uses. As illustrated, the upper end of thepost528 could also include a T-shaped or oversized head529 (which could have a spherical, pyramidal, conic, or cubic shape). Alternatively, the head could have one or more transversely extending, deformable cross-members, an L-shaped hook-like member, or another type of projection for at least temporarily capturing the pumping or mixingelement502 to prevent it from inadvertently falling off when not in use. Of course, the positioning of thehead529 for capturing the pumping or mixingelement502 is preferably selected such that it does not interfere with the free levitation or rotation. As should be appreciated, thepost528 provides not only centering function, but also holds the pumping or mixingelement502 in place in case it accidentally decouples during the pumping or mixing operation. This significantly eases the process of returning the pumping or mixingelement502 to the proper position for initiating or resuming levitation/rotation by the corresponding system (which may be, for example,systems10,100,200,300,800 etc.).
• InFIG. 14b, thispost528 is adapted to receive the pumping or mixingelement502, which has a corresponding opening (and thus, may be annular or have any other desired shape or size). Since thepost528 preferably includes anoversized head portion529 that keeps the pumping or mixingelement502 in place, including before a fluid is introduced, thevessel500 may be manufactured, sealed (if desired), shipped, and stored prior to use with the pumping or mixingelement502 already in place. Thevessel500 may also be sterilized as necessary for a particular application, and in the case of a flexible bag, may even be folded for compact storage. As should be appreciated, thepost528 also serves the advantageous function of keeping the pumping or mixingelement502 substantially in place (or “centered”) should it accidentally become decoupled from the adjacent motive device, which as in this case is a rotating annularsuperconducting element106. However, the centeringpost528 could also be used in the embodiment ofFIG. 9 as well by simply forming a center opening in the pumping or mixingelement204.
• In the illustrated embodiment, thepost528 is shown as being formed by an elongated rod-like structure inserted through one of thenipples530 typically found in the flexible plastic bags frequently used in the bioprocessing industry (pharmaceuticals, food products, cell cultures, etc.). Theoversized head portion529 is preferably formed of a material that is sufficiently flexible/deformable to easily pass through the opening in thenipple530. Aconventional clamp531, such as a cable or wire tie, may be used to form a fluid-impervious seal between thenipple530 and the portion of thepost528 passing therethrough, but other known methods for forming a permanent or semi-permanent seal could be used (e.g., ultrasonic welding in the case of plastic materials, adhesives, etc.). Anyother nipples530 present (shown in phantom inFIG. 14b) may be used for introducing the fluid prior to mixing, retrieving a fluid during mixing or after mixing is complete, or circulating the fluid in the case of a pumping operation. Advantageously, the use of the rod/nipple combination allows for easy retrofitting. Nevertheless, instead of using a separate rod, thepost528 may be integrally formed with the material forming thevessel500, either during the manufacturing process or as part of a retrofit operation. Also, as noted in my prior applications, theoversized head portion529 may be cross-shaped, disc-shaped, L-shaped, Y-shaped, or may have any other desired shape, as long as the corresponding function of capturing the pumping or mixingelement502 is provided. Thehead portion529 may be integrally formed, or alternatively may be provided as a separate component that is clamped or fastened to thepost528.
• In yet another embodiment, thevessel500 may also include a structure that helps to ensure that proper alignment is achieved between the centeringpost528 and an adjacent structure, such as a device for rotating and/or levitating the pumping or mixingelement502. In the embodiment ofFIG. 14b, this alignment structure is shown in the form of analignment post532 projecting outwardly from thevessel500 and co-extensive with the centeringpost528. Thepost532 extends through anopening536 formed in the lower portion, such as the floor, of asemi-rigid support container534 defining a compartment for receiving thevessel500. The container543 thus serves as a support structure (which may instead be the table T, as shown inFIG. 14e).
• The adjacent motive device, which as shown as including acryostat102 containing a rotatingsuperconducting element106, includes alocator bore533. This bore533 is concentric with thesuperconducting element106 and is sized and shaped for receiving the alignment post532 (which may have any desired cross-sectional shape, including circular, elliptical, square, polygonal, etc.). As a result of the centering andalignment posts528,532, assurance is thus provided that the pumping or mixingelement502 is in the desired position for forming a coupling with an adjacent motive device, such as thecryostat102 housing the rotating superconducting element106 (which may both rotate together, as described above). This is particularly helpful for properly aligning the pumping or mixingelement502 with the cryostat, such ascryostat102, in the case of opaque vessels or adjacent containers, sealed or aseptic containers, large containers, or where the fluid is not clear. Instead of forming thealignment post532 from an elongated rod inserted into anipple530 or the like, it should be appreciated that it may also be integrally formed with thevessel500 during manufacturing, or later during a retrofit.
• FIG. 14balso shows the centeringpost528 projecting upwardly from a bottom wall of thevessel500, but as should be appreciated, it could extend from any wall or other portion thereof. For example, as illustrated inFIG. 14c, the rod serving as both the centeringpost528 and thealignment post532 may be positioned substantially perpendicular to a vertical plane. Specifically, in the particular embodiment shown, thevessel500 is an empty flexible bag as shown above positioned in a rigid orsemi-rigid support container534 having anopening536 formed in the lower portion thereof. Once thevessel500 is inserted in thecontainer534, but preferably prior to introducing a fluid, thealignment post532 is positioned in theopening536 such that it projects therefrom (along with any inlet or outlet hoses present). The proximal end of thealignment post532 is then inserted into a corresponding receiver in the motive device, such as the locator bore533 formed in the cryostat102 (which is easily reoriented, as described herein). This ensures that the pumping or mixingelement502 is in the desired position to form the magnetic coupling with the superconducting once field cooling is complete to achieve levitation and/or rotation without the need for external intervention. As noted above, the coupling may be formed either before or after the introduction of the fluid into thevessel500. Also, while shown in conjunction with a particular embodiment of the pumping or mixing system, it should be appreciated that the alignment and centeringposts528,532 may, either together or separately, be used in conjunction with different types of pumping or mixing elements or with any of the pumping or mixing systems disclosed herein.
• In many of the above-described embodiments, the pumping or mixing action is essentially localized in nature. This may he undesirable in some situations, such as where the vessel is relatively large compared to the pumping or mixing element. To solve this problem, the particular system used to supply the pumping or mixing action may be provided with a motive device for physically moving the superconducting element (which may also be simultaneously rotated). This of course will cause the levitating pumping or mixing element to follow a similar path.
• With reference to the schematic view ofFIG. 14d, and by way of example only, the particular arrangement is shown in use on thesystem100 ofFIG. 5, but with thebag500 ofFIG. 14. In addition to amotive device540 for rotating the first portion of thecryostat102a(which may comprise the bearing(s)120,endless belt128,motor131, shaft, and pulley) and acooling source541, thesystem100 may include asecond motive device542. In one embodiment, this second motive device542 (shown schematically in dashed line outline only inFIG. 14c) is capable of moving the first portion of thecryostat102a,and hence thesuperconducting element106, to and fro in a linear fashion (see action arrow L inFIG. 14c). Thus, in addition to levitating and rotating the pumping or mixingelement502, the side-to-side motion allows it to move relative to thebag500 or other vessel containing the fluid. This advantageously permits non-localized pumping or mixing action to be provided. Thesecond motive device542 may include a support structure, such as a platform (not shown) for supporting all necessary components, such as the first portion of thecryostat102a(or the entire cryostat, such as in the embodiment ofFIG. 9), thefirst motive device540 for rotating one of the superconducting element106 (or the pumping or mixingelement502 such as in the embodiment ofFIG. 9), and the cooling source541 (which may form part of the cryostat as shown inFIG. 9, or may be a separate component altogether, as shown inFIG. 2). Instead of using a linear motion device, it should also be appreciated that thesecond motive device542 may be capable of moving thesuperconducting element106 in a circular or elliptical path relative to the fixed position of thebag500 or other vessel, or in any other direction that will enhance the overall mixing or pumping action provided by the rotating pumping or mixingelement502. Also, thebag502 or vessel may be separately rotated or moved to further enhance the operation (see the above-description of the embodiment ofFIG. 3).
• Ensuring that the pumping or mixing elements are both proper for a particular system and are of the correct shape and size may also be important. To do so, it is possible to provide a transmitter in one of the pumping or mixing element or the vessel for generating a signal that is received by a receiver in the system (or vice versa), such as one positioned adjacent to the superconducting element or elsewhere. An example of one possible configuration is shown inFIG. 14, wherein thetransmitter550 is provided on the pumping or mixingelement502 itself and thereceiver560 is positioned in the cryostat102 (but seeFIG. 14a, wherein thetransmitter550 orreceiver560 is provided in thebag500 serving as the vessel). A controller for the system, such as a computer (not shown) or other logic device, can then be used to maintain the system for rotating the pumping or mixingelement502 in a non-operational, or “lock-out,” condition until the receiver andtransmitter550,560 correspond to each other (that is, until thetransmitter550 generates an appropriate signal that is received by the receiver560). The transmitter/receiver combination employed may be of any type well known in the art, including electromagnetic, ultrasound, optical, or any other wireless or remote signal transmitting and receiving devices.
• In accordance with another aspect of the invention, a kit is also provided to assist in the set-up of any of the systems previously described. Specifically, and as briefly noted in both this and my prior applications, it is necessary during field cooling to cool the superconducting element to below its transition temperature in the presence of a magnetic field in order to induce levitation in a permanent magnet producing the same magnetic field. This cooling process causes the superconducting element to “remember” the field, and thus induce the desired levitation in the pumping or mixing element each time it or any other magnet having either a substantially similar or identical magnetic field distribution is placed over the superconducting element. While it is possible to use the pumping or mixing element itself to produce the magnetic field required during field cooling, oftentimes the pumping or mixing element will be sealed in the vessel or container. This makes it difficult, if not impossible, to ensure that the magnets held therein are properly aligned and spaced from the superconducting element during field cooling.
• One way to overcome this potential problem is to use a set-up kit. As illustrated inFIG. 15, the set-up kit may comprise at least onecharging magnet600 having a size, shape, and magnetic field distribution that is identical to the levitation magnet contained in the particular pumping or mixing element slated for use in one of the pumping or mixing systems previously described. The chargingmagnet600 is placed adjacent to thesuperconducting element602, such as on the upper surface of thecryostat604, table (not shown), or other structure. As illustrated, the chargingmagnet600 may further include aspacer606. Thisspacer606 allows the chargingmagnet600 to simulate the spacing of the pumping or mixing element (not shown) above thesuperconducting element602 during field cooling. This ensures that the desired levitation height is achieved for the pumping or mixing element (not shown) once the vessel is in position. Thespacer606 is formed of a non-magnetic material to avoid interfering with the charging process. By providing a variety of different sizes, shapes, and configurations of charging magnets in the kit (e.g., annular magnets), it is possible to easily perform field cooling for any corresponding size or shape of levitation magnet in the corresponding pumping or mixing element, and then simply place the vessel containing the pumping or mixing element over thesuperconducting element602 to induce the desired stable, reliable levitation. It is also possible to field cool thesuperconducting element602 while thecryostat604 is in one orientation, and then reorient it for forming the coupling with the pumping or mixing element (see, e.g.,FIG. 14c).
• During field cooling, and regardless of whether the pumping or mixing element or aseparate charging magnet600 is used to produce the charging magnetic field, it is possible to unintentionally or accidentally induce an undesired magnetic state in thesuperconducting element602, such as if the position of the pumping or mixing element (not shown) or chargingmagnet600 is not correct. Since improper charging may prevent the pumping or mixing element from levitating in a stable fashion, recharging thesuperconducting element602 may be required. To facilitate recharging the superconducting element, it is provided with a heater H, such as an electric heating coil (not shown). By energizing this coil using a power supply P or other source of electrical current (not shown), thesuperconducting element602 may be quickly brought up from the transition temperature for recharging. As shown schematically, the power supply P is preferably positioned externally to thecryostat604. Once the position of the pumping or mixing element or chargingmagnet600 is adjusted or corrected, the heater H may be turned off and the superconducting element once again allowed to cool to the transition temperature in the presence of the desired magnetic field. Yet another embodiment of asystem700 is provided for use with a particular type of vessel including a cavity, such as of the type designed to withstand high internal pressures. Even with this cavity, thesystem700 permits a strong magnetic coupling to be formed between an external magnet or superconductor and one or more magnets forming part of an internal mixing element, such as a rotor or impeller, inside the vessel to ensure that stable, reliable levitation is achieved.
• As shown in the schematic, partially cross-sectional side elevational view ofFIG. 16, thevessel702 includes a cavity704 formed in one sidewall thereof. As briefly explained above, the shape of this cavity704 is preferably cylindrical. In the cylindrical case, this shape allows for the outer sidewall of the cavity704 to be fabricated having a first thickness t₁(about 2 millimeters in one possible embodiment, but possibly even less), with the remainder of thevessel702 being formed from the same or a different material having a second, greater thickness t₂(e.g., more than 2 millimeters, and preferably about 7 millimeters). To form a unitary vessel, the cavity704 may be formed as a separate “hat-shaped” section, including an annular flange that is welded (seeweld705 inFIG. 16) to a corresponding flange (not numbered).
• With this construction, thevessel702 is able to withstand relatively high internal pressures (up to about 7 bar, and possibly greater), yet the relatively thin sidewall of the cavity704 allows for strong magnet-magnet/magnet-superconductor interactions to be achieved. Of course, the potential reduction in thickness of the sidewalls of the cavity704 and the upper limit of the internal pressure are directly influenced by the type of material used, with the dimensions provided above corresponding to avessel702 formed of conventional non-magnetic stainless steel. Although a cylindrical cavity704 is shown, it should be appreciated that other equivalent geometric arrangements may also be used, including those having regular or irregular polygonal cross-sections or the like.
• To adapt the superconducting levitation scheme described immediately above to avessel702 having such a cavity704, a special “cryostat”706 may be used, which is generally similar in construction to the one shown inFIG. 9. In the illustrated embodiment, thecryostat706 includes anexternal wall708 that defines an enclosed space or chamber (not numbered). This space is evacuated, such as by using a vacuum source (not numbered), and together with thewall708 creates a vacuum “jacket”710 around a superconductor orsuperconducting element712 held therein. Thesuperconducting element712 is preferably a “high temperature” superconducting element formed of melt-textured ReBa₂Cu₃O_x, with Re representing a rare earth element (e.g., Yttrium, of which YBCO is a common example), but the use of other such materials either already known or discovered after the filing is of course possible without departing from the broadest aspects of the invention. Also, as is known in the art, thesuperconducting element712 may be formed from a single annular or ring shaped piece of material, or as outlined further in the description that follows, may be comprised of a plurality of contiguous or non-contiguous segments or sections, each formed of a piece of superconducting material interconnected or arranged in an annular or substantially polygonal configuration.
• In the illustrated embodiment, thesuperconducting element712 is positioned in a “head” portion of thecryostat706 sized and/or otherwise adapted for extending or projecting into the cavity704 formed in thevessel702. Thecryostat706 also includes or houses athermal link714 for supplying the cooling that keeps theelement712 in the desired superconducting state. As described above, thethermal link714 is preferably formed of a material having a high degree of thermal conductivity/low thermal resistance (metals, such as copper, brass, or the like). Although not critical, thelink714 may include an engagement portion corresponding generally in size and shape to thesuperconducting element712 to ensure that the desirable full contact and engagement is established between the corresponding surfaces to improve thermal transfer. As also described above, thethermal link714 is connected to a cooling source, such as a Dewar flask filled with a liquid cryogen, a closed cycle refrigerator, or the like (see, e.g.,FIG. 9). It should be appreciated by skilled artisans that the particular cooling source or thermal link used is not important or critical, as long as it is capable of maintaining theelement712 in the desired superconducting state to induce levitation in themixing element722.
• As with the embodiment inFIG. 9, theouter wall708 of thecryostat706 may be configured to create a bore or opening that allows for ashaft716 or the like to pass therethrough (seeFIG. 16a). One end of theshaft716 is coupled to a motive device, such as amotor718, while the other carries a plurality or array ofdrive magnets720. Thedrive magnet array720 is preferably positioned in close proximity to the inside surface of the sidewall of the cavity704, and is comprised of a plurality of magnets having alternating polarities or polar orientations (with the N-S poles preferably being arranged perpendicular to the vertical plane and spaced sufficiently close to the wall of the cavity704 to create the strongest possible magnetic coupling, and hence, the most efficient torque transfer).
• Turning now to themixing element722, it is preferably in the form of a rotor or impeller comprised of a hollow, substantially cylindrical or tubular body sized so as to permit a concentric orientation with the cylindrical cavity704 inside thevessel702. The mixingelement722 may comprise alevitation magnet724 generally corresponding in shape and proportional in size to thesuperconducting element712, and preferably having its poles oriented in a direction parallel to a vertical plane. Spaced from thelevitation magnet724, and preferably embedded in a matrix material M, is an array of strategically positioned drivenmagnets726. The drivenmagnets726 correspond generally in size and shape to the array of alternatingpolarity drive magnets720 carried on theshaft716. The drivenmagnets726 are also of alternating polarity to create the desired magnetic coupling with thedrive magnets720 for transmitting the drive torque from the motive device, such as the motor, to theshaft716, and ultimately to thelevitating mixing element722. As shown inFIG. 16, the mixingelement722 may also carry one ormore blades728, vanes, or the like to further enhance the mixing action provided (or pumping action, in the case of a pumping chamber having a cavity bottom).
• Hence, as depicted inFIG. 16, it is possible to easily adapt themixing system700 for use with avessel702 having a thin-walled cavity704 that is nevertheless capable of withstanding high pressures, such as those possibly created during cleaning or sterilization. As an example of one possible application, thevessel702 may thus be pre-sealed with the magnetic mixing element722 (e.g., rotor or impeller) inside, and then simply placed over thecryostat706, such as by positioning the vessel on an adjacent stable support surface, such as a table, support platform, stand or the like (see reference character T inFIG. 16). Assuming that field cooling has previously been completed (such as by using a “kit” for supporting a corresponding “set-up” magnet adjacent to thesuperconducting element712 during cooling, which in this case could be an annular set-up magnet, as opposed to the disc-shaped one inFIG. 15), thevessel702 is simply positioned over thecryostat706, as shown inFIG. 16, such that the magnetic field of thepermanent levitation magnet724 creates the desired flow of current through thesuperconducting element712 to achieve the simultaneous attraction and repulsion that results in stable levitation.
• During experimentation using thesystem700, it was discovered that it may be advantageous in terms of levitational stability to form thesuperconducting element712 of a plurality of segments of the melt-textured/melt-processed rare-earth superconductor described above, with the particular orientation of the crystallographic axis or planes of each segment being selected to significantly enhance the magnetic stiffness of the coupling, as well as the load capacity of thelevitating mixing element722. Specifically, as shown inFIG. 17, which is a plan schematic view of thelevitation magnet724 and a plurality ofsegments712a. . .712nformed of a superconducting material having crystallographic planes (see below) and arranged in a non-contiguous polygonal configuration, andFIG. 18, which is a cross-sectional view of the same taken along line18-18 ofFIG. 17, the crystallographic “C-axis” of eachsuperconducting segment712a. . .712nis oriented in a radial direction, or in the illustrated embodiment, substantially perpendicular to the magnetization vector of thelevitation magnet724, and preferably passes through the center thereof. Accordingly, the A-B planes are oriented substantially parallel to the polar magnetization axis of thelevitation magnet724. Superconducting materials having these crystallographic planes/axes include those comprised of ReBa₂Cu₃O_x, formed by a melt-texturing or “melt-processing” as is known in the art (see, e.g., U.S. Pat. No. 5,747,426 to Abboud, the disclosure of which is incorporated herein by reference).
• Using this arrangement, it was found that the levitation force, magnetic stiffness, and concomitant load capacity of thelevitation magnet724 is increased on the order of two to three times without a corresponding change in any other parameter of thesystem700 described above. Of course, these increases serve to enhance the rotational stability of the mixingelement722 when such an arrangement is used in a pumping or mixing system, which in turn improves the operational reliability. These increases also advantageously reduce the tendency of the pumping or mixingelement722 to decouple at higher rotational speeds or in pumping or mixing high viscosity fluids or the like.
• It is also noted that thesystem700 is generally described above as a mixing system for use withvessels702 or containers capable of withstanding high pressures. However, it should also be appreciated that thesystem700 could also be used for the mixing or pumping of fluids through avessel702 in the form of a flexible, open-top container or any other type of container having the cavity704 or a similar configuration. Of course, the strategic orientation of the elements of a segmented superconductor could also be used to enhance the levitational and rotational stability of a pumping or mixing element used in any of the systems described herein as well.
• Yet another embodiment of a pumping or mixing system800 is proposed inFIG. 19. Perhaps the best way to describe this embodiment is to begin with a description of thevessel810 and the pumping or mixingelement812. Thevessel810, likevessel702, is preferably created having acavity814 that defines a concentric annular protrudingportion815. Preferably, the wall defining each side ofcavity814 and each side of theannular portion815 is fabricated of a relatively thin, non-magnetic material, such as stainless steel. As noted above with regard tovessel702, by forming the remainder of thevessel810 having relatively thick sidewalls, it may withstand high pressures, such as those created during sterilization using steam under pressure or the like. However, in the case where thevessel810 is not subjected to high pressures or is used as a pumping chamber, the walls may be formed of a substantially homogeneous material (disposable plastics, glass, stainless steel, etc.) having substantially the same relative thickness. A description of an embodiment wherein a flexible plastic bag is provided with a cavity is described below and shown inFIG. 22.
• The pumping or mixingelement812 is capable of being positioned in thevessel810 and includes alevitation magnet816. In particular, thelevitation magnet816 is sized and shaped for extending into the interior of theannular portion815 of thevessel810. In the illustrated embodiment, thelevitation magnet816 is polarized in the vertical direction (the specific orientation of the poles is not critical) to create a vertical magnetization vector. However, the magnetization vector could also be oriented in a horizontal or substantially horizontal plane (although those skilled in the art will recognize that forming a single ring shaped magnet having opposite poles oriented in a horizontal plane is more difficult than forming one having a vertical magnetization vector).
• To levitate the pumping or mixing element in thevessel810, at least one, and preferably a plurality of superconducting elements818 are positioned in anannular cryostat802. Thiscryostat802 is specially adapted for receiving the annular protrudingportion815 of the vessel810 (seeFIG. 19a) and may even support the vessel, as shown inFIG. 19. More specifically, in the illustrated embodiment, thecryostat802 includes anannular channel806 for receiving the correspondingannular portion815 of thevessel810. Theouter wall808 of thecryostat802 defines a space or chamber that is preferably evacuated to create a vacuum jacket, as described above. Alternatively, the chamber could be filled with an insulating material to reduce the thermal transfer. Regardless of the means used, the important point is that in the case of pumping or mixing non-cryogenic, warm or temperature sensitive fluids, no or only negligible thermal transfer from the cold superconductor to the vessel and hence the fluid results.
• Preferably, the superconducting elements818 are comprised of a plurality of segments, each of which is in thermal communication with a cooling source (e.g., a Dewar flask or a closed-cycle refrigerator) via athermal link820 positioned and supported in thecryostat802. The segments comprising each of the one or more superconducting elements818 are preferably formed of a “high-temperature” superconducting material having crystallographic A-B planes and a C-axis, which as noted above, is a characteristic of melt-textured or melt-processed ReBa₂Cu₃O_x, with Re representing a rare earth element (e.g., Yttrium, of which YBCO is a common example).
• In the preferred embodiment, threesuperconducting elements818a,818b,818care provided on thethermal link820, although it should be appreciated from reviewing the description that follows that using only a single superconducting element or two superconducting elements to levitate the pumping or mixingelement812 is entirely possible (seeFIG. 16). A first of thesuperconducting elements818ais positioned adjacent to a first side of theannular channel806 formed in thecryostat802 adjacent to a first side of theannular levitation magnet816. The secondsuperconducting element818bis also positioned adjacent to a second side of theannular levitation magnet816. The thirdsuperconducting element818cis positioned adjacent to a third side of theannular levitation magnet816. Each of thesuperconducting elements818a,818b,818emay be in thermal communication with the samethermal link820, as shown inFIG. 19 and positioned internal to thecorresponding cryostat802, which by way of insulation or vacuum jacket prevents any thermal transfer to theroom temperature vessel810, the fluid F held therein, or the pumping or mixingelement812.
• In a most preferred version of this embodiment, the crystallographic planes/axes of the segments forming thesuperconducting elements818a,818b,818care oriented so as to significantly improve the levitation force, the resulting loading capacity, and the magnetic stiffness of the coupling formed with the pumping or mixingelement812. Specifically, the first and thirdsuperconducting elements818a,818c(or more particularly, the segments comprising these elements) are oriented such that the C-axes thereof are perpendicular to the magnetization vector of thelevitation magnet816, while the secondsuperconducting element818bis oriented such that the C-axis of each segment thereof is aligned with and parallel to the magnetization vector of thelevitation magnet816. Another way to describe the arrangement is that the A-B crystallographic planes of the first and thirdsuperconducting elements818a,818care parallel to the axis of polarization of thelevitation magnet816, while the A-B crystallographic planes of the secondsuperconducting element818bare perpendicular to the polarization axis (note the substantially parallel lines representing the A-B planes drawn on each superconducting element818a-cinFIG. 19). As used herein, the terms “parallel” and “perpendicular” are intended to mean generally or substantially parallel or perpendicular, it being recognized that variations in the orientation of the various crystallographic planes or axes relative to the magnetization vector are either inherent or may be created by slight misalignments of adjacent elements, or may be intentionally varied within a range to adjust or fine tune the levitation force provided or rotational stability.
• The particular arrangement shown inFIG. 19 results in a system800 in which the pumping or mixingelement812 is levitated in a most stable fashion. This stable levitation results primarily from the interaction between the specially oriented segments forming each superconducting element818a-cand theannular levitation magnet816. As a result of this arrangement, the loading capacity of the pumping or mixing element is increased, as it the stiffness of the magnetic coupling. This combination allows for a greater amount of torque to be supplied to the pumping or mixingelement812 without accidental decoupling, which allows for higher angular velocities to be achieved. It also allows for use of the system800 with fluids having higher viscosities.
• The drive system for rotating the pumping or mixing element may be substantially as described above. Specifically, a shaft822 coupled at one end with a motive device, such as amotor824, is positioned in a room temperature bore or through an opening formed in thecryostat802. The end of the shaft822 adjacent to thevessel810 carries a plurality ofdrive magnets824 having alternating polarities. Corresponding driven magnets826 having alternating polarities are provided on the pumping or mixingelement812. As shown inFIG. 19, the pumping or mixing element may also includeimpeller blades828, vanes, or like structures to further enhance the pumping or mixing action provided.
• In accordance with yet another embodiment of the present invention, a specific pumping or mixingsystem900 using a rotatingsuperconducting element901 is shown inFIG. 20. Thesuperconducting element901 may be supported by aplate902 in thermal engagement with a cooling source forming a part of acryostat903 and preferably rotating therewith. Thesuperconducting element901 is surrounded by awall905 defining an evacuatedchamber906, which may together be considered to form a vacuum jacket comprising part of the cryostat903 (although as described above thechamber906 could also be insulated or any other known or yet-to-be discovered means for obviating thermal transfer between a cold superconducting element could be used).
• In the illustrated embodiment, the cooling source is a portable refrigerator or “cryocooler”904 that also forms part of thecryostat903. Thecryocooler904 is shown as having a “head”end905 that extends into thechamber906 to directly engage and support theplate907 which in turn supports thesuperconducting element901, although the use of a separate thermal link (not shown) is also possible, depending on the relative dimensions of the system. As with the thermal link previously described, both theplate902 and thehead end907 of the cryocooler are typically formed of a material having a high degree of thermal conductivity/low thermal resistance (e.g., a metal) to ensure that the desirable efficient thermal transfer is established. Theplate902 may also be supported from thewall905 by one or more connectingmembers908, which are preferably thin, but relatively strong, and formed of a material having a low degree of thermal conductivity so as to create only negligible thermal transfer to thewall905.
• Thecryostat903 is rotatably supported by at least one, and preferably a pair of bearings or bearingassemblies909a,909b,which are in turn supported by a stable support structure, such as an adjacent vertical wall VW or another type of support frame (which may or may not engage the adjacent structure, such as table T, supporting the vessel). For example, one bearing may engage theouter wall905 of thecryostat903, while the other engages the outer wall of thecryocooler904. The use of two bearingassemblies909a,909bof course ensures that thecryostat903 rotates about a vertical center axis in a most stable and reliable fashion and is capable of resisting any skewing forces, and may also allow it to be turned on its side (such as it would appear ifFIG. 20 is oriented in a landscape view, rather than a portrait view). As shown inFIG. 20, the bearingassemblies909a,909bmay include mechanical roller or ball bearings, or other elements that may provide low-friction, rotatable support thecryostat903.
• To transmit the desired rotational motion, anendless belt910 may be placed in frictional engagement with afirst pulley911 coupled to or carried by thecryostat903. Thebelt910 also engages asecond pulley912 supported by theshaft914 of amotive device916, such as a variable speed electric motor. As should be appreciated, the rotation of theshaft914 thus causes thecryostat903, and hence, thesuperconducting element901 positioned therein to rotate. As noted above, thecryostat903 could also be mounted “inline” on a shaft that is in turn connected or coupled directly to a motive device, such as an electric motor.
• One particularly preferred example of a commercially available closed-cycle refrigerator orcryocooler904 for use in the present invention is a type of substantially self-contained, compact, closed-cycle cryocooler employing the Stirling cycle to produce the desired refrigeration, several models of which are manufactured and distributed by Sunpower, Inc. of Athens, Ohio. As shown schematically inFIG. 20, thiscryocooler904 includes alower portion904awhich serves to house an electric motor and anupper portion904badjacent to thehead907 which houses a reciprocating piston (not shown). In light of the commercial availability of several suitable models, the workings of such a cryocooler need not be understood to practice the present invention. However, it is noted that Sunpower, Inc. holds a number of U.S. patents on various types of cryocoolers, each of which is incorporated herein by reference to the extent deemed necessary to allow a skilled artisan to make or use this invention. Regardless of the type of cooling source used, the important point is that it is fully capable of generating the “high temperatures” (e.g., 77K-90K) necessary to induce a superconducting state in, for example, a YBCO superconducting element (which may be comprised of a plurality of segments, as described below).
• To supply the necessary power to thecryocooler904 such that it keeps thesuperconducting element901 at the desired temperature, yet allows it to rotate even at high speeds, a dynamic electrical connection is provided. Specifically,contacts918, which are shown in the form of annular rings surrounding the outer wall of thecryocooler904, are provided for engaging corresponding “stationary” flexible or pivotingcontacts920 in electrical communication with a power source922 (120/220V), which may be remote. As should be appreciated, this configuration allows thecryocooler904 to freely rotate at both high and low speeds while continuously receiving the power necessary to run the motor/drive the piston and keep thehead end907 at the desired cold temperature. Instead of this illustrated configuration, a well-known type of dynamic electrical connection called a “slip ring” may be used, such as those manufactured by Siemens, Litton, and the Kaydon Corp. A slip ring is also sometimes referred to in the art as a “rotary electrical interface,” a “commutator,” a “swivel.” or a “rotary joint.”
• The system described above can be substituted into thesystem100 shown inFIGS. 5-7 for rotating a pumping or mixing element in the form of a flat, disc-shaped rotor orimpeller134 for pumping or mixing a fluid in a flat-bottomed rigid vessel or bag. In that case, theplate902 could be eliminated and a disc-shaped superconducting element, such aselement106, used in its place. However, inFIG. 20, thevessel922 is illustrated having acavity924, which may of course be similar in construction to the cavity provided in a vessel capable of withstanding high internal pressures, as described above and shown inFIG. 16. Alternatively, thecavity924 could be formed in a conventional open-top vessel, in a flexible bag or container (seeFIG. 22), or in any other type of vessel used in applications where high pressures are not a concern. In the case where thecavity924 is formed in a flexible bag or container, as shown inFIG. 22, is should also be appreciated that thecavity924 may serve a function similar to that of centeringpost528 shown inFIG. 14b(and could even include a peripheral flange, projections, or like structures at the upper end to ensure that the pumping or mixingelement926 remains fully held in place during shipping, storage, or between uses, yet spaced far enough away to avoid creating any interference with the desired levitation/rotation).
• In any case, in the embodiment inFIG. 20, the pumping or mixingelement926 is substantially cylindrical and includes only alevitation magnet928, since both the levitation force and the driving torque are provided by thesuperconducting element901. Thislevitation magnet928 may be comprised of a plurality of segments ofpermanent magnets928a. . .928nhaving alternating polarities and arranged in a substantially annular or polygonal configuration (see the schematic illustration merely showing a preferred orientation/arrangement inFIG. 21). As also shown schematically inFIG. 21, thesuperconducting element901 is concentric with thelevitation magnet928 and is also comprised of a plurality ofsegments901a. . .901narranged in an annular or polygonal configuration. Preferably, eachsegment901a. . .901nis oriented having its crystallographic C-axis aligned in the radial direction (i.e., oriented generally parallel to the magnetization vector of acorresponding segment928a. . .928nof thepermanent magnet928, and preferably passing substantially through the center thereof). Accordingly, the A-B planes of thesegments901a. . .901ncomprising thesuperconducting element901 are oriented generally perpendicular to the radial direction, and hence, the magnetization vector. As a result of this arrangement, the rotatingsuperconducting element901 not only reliably induces stable levitation in the pumping or mixingelement926 vialevitation magnet928, but also forms a magnetic coupling which causes the pumping or mixingelement926 to rotate. As shown inFIG. 20, the pumping or mixingelement926 may also carry one or more impeller blades, vanes, wings, or likestructures930 to further enhance the pumping or mixing action.
• FIG. 23 shows an embodiment of the pumping or mixingsystem950 for use with a vessel (such as a tank K, but any vessel disclosed herein would also work) having a cavity that is generally similar to the embodiment shown inFIG. 20 with a few modifications. The first is that therotating cryostat952 includes two arrays ofsuperconducting elements954,956, with each array spaced in the vertical direction. The pumping or mixingelement958 includes corresponding arrays of alternatingpolarity magnets960,962 (see, e.g.,FIG. 21), with each magnet in thearray960 having a neighboring magnet with an alternating polarity. The rotation of thecryostat952 and, hence, the superconducting,element arrays954,956 thus induces both levitation and rotation in the pumping or mixing element958 (which is shown having a plurality of upstanding blades B). As should be appreciated, the dual arrays enhance the vertical stiffness of the coupling and improve torque transfer.
• Thesuperconducting element arrays954,956 are supported on a thermallyconductive platform963 by an upstandingcylindrical wall964. Theplatform963 in turn is coupled to arod965 serving as a thermal link to a cooling source, such as the SUNPOWER cryocooler described above or a Dewar flask filled with a liquid cryogen, which is in turn coupled to a motive device (shown in block form only, but seeFIG. 20 for an example of one possible embodiment). As noted above, insulating or evacuating thechamber966 in thecryostat952 prevents the coldsuperconducting element arrays954,956 from cooling the adjacent tank K to any significant degree, which means that the system is well-adapted for pumping or mixing non-cryogenic fluids, including room-temperature fluids.
• The embodiment ofFIG. 23 also differs from the one shown inFIG. 20 in that the pumping or mixingelement958 carries a first ring magnet968 (or an equivalent array of magnets, such as vertically polarized magnetic discs (not shown)). A corresponding ring magnet970 (or array of magnets) is carried by the rotating cryostat952 (preferably externally and at the top, as shown inFIG. 23). Thefirst ring magnet968 and thesecond ring magnet970 are oriented such that like poles are adjacent to each other. This magnet-magnet interaction thus repels the pumping or mixingelement958 from thecryostat952. However, the interaction between thesuperconducting element arrays954,956 and the arrays ofmagnets960,962 together generally levitate and hold the pumping or mixingelement958 in place. The net result is that the pumping or mixingelement958 is levitated, but is able to resist any force tending to move it into contact with the tank K, including the outer surface of the adjacent cavity.
• Another distinction in the illustrated embodiment is that the pumping or mixingelement958 is generally cylindrical and includes anopening967. As a result of this construction, when the pumping or mixingelement958 is rotated, fluid is drawn into the gap between it and the adjacent cavity in the tank K (see action arrows F). The fluid then passes through theopening967, which enhances the fluid agitation created by the rotation of the pumping or mixingelement958, even at relatively low angular velocities.
• A related embodiment is shown inFIG. 24. In this embodiment, the first ring magnet968 (or array) is again provided on or in the pumping or mixingelement958, but the second ring magnet970 (or array) is positioned external to the tank K. Again, therings968,970 have like polarities along the adjacent faces to create a repelling force. In this case, this force helps to prevent the pumping or mixingelement958 from “bottoming out” on the adjacent surface of the tank K. Although not preferred for most applications due to the clean-up and sterilization problems possibly created, thesecond ring magnet970 could be positioned just inside the tank K as well. Instead of attaching thering magnet970 to the tank K, it could also be supported by thecryostat952, such as a flange (note dashed lines inFIG. 24) or a related structure that rotates therewith. Also, the possibility of providing neighboring magnets in eacharray960,962 with like polarities is shown (with the polarities of vertically adjacent magnets in each array still alternating), which is somewhat less preferred than the embodiment ofFIG. 23 in which the polarities of neighboring magnets in each array alternate.
• These two approaches could also be combined into the same system, as shown inFIG. 25. In particular, first andsecond ring magnets968a,970aare provided in one portion of the pumping or mixingelement958, and third andfourth ring magnets968b,970bare provided in another. The repelling forces created thus provide dual levels of protection against the rotating pumping or mixingelement958 inadvertently contacting the vessel or tank K. Also, either or both approaches could be used in the embodiments ofFIG. 16 or19 as well. Also note that the polarities of adjacent magnets in thearrays960,962 are alike, although each vertically adjacent pair has a different polarity that the next-adjacent pair. This is somewhat less preferred than the arrangement ofFIG. 23 in terms of stiffness, but would work nevertheless.
• By switching the polarities, it is also possible to provide one or more sets of magnets likering magnets968,970 that attract, rather than repel each other. The attractive force thus created may help to prevent the pumping or mixingelement958 from moving in a vertical direction relative to the cavity as it rotates (or in the horizontal direction, in the case where the cavity is positioned with its centerline axis parallel to a horizontal plane). The magnets would preferably be sufficiently weak in power to avoid creating any instability in the levitation and/or rotation induced by thesuperconducting element arrays954,956.
• FIGS. 26 and 27 show a method and apparatus for centering and setting up a pumping or mixingelement980 that is capable of levitating in avessel981, such as in a hermetically sealed tank, in a sterile vessel, such as a flexible bag, or even in an open-top vessel where access to the corresponding surface adjacent to levitating the pumping or mixing element is restricted. Thevessel981 includes acavity982, as described above. Inside thevessel981, thecavity982 may include along its outer surface an engagement structure for contacting, engaging, or supporting the pumping or mixingelement980 when in a non-levitating or resting position. In the preferred embodiment, this engagement structure comprises a frusto-conical surface984 that is tapered relative to the horizontal plane. The pumping or mixingelement980, which is of course generally annular, includes amatching surface986 along at least a portion of an adjacent inner surface thereof. Preferably, the matchingsurface986 is formed in an inert portion of the pumping or mixingelement980, such as the matrix material (e.g., plastic, metal, composites, etc.) used to support the levitation magnet or magnet array988 (which is shown schematically, but could be any appropriate one of the arrangements described herein). The pumping or mixingelement980 is shown slightly raised in the vertical direction to illustrate the shape of thesurfaces984,986. However, it should be appreciated that thesesurfaces984,986 would normally be in contact with each other as the result of gravity when the pumping or mixingelement980 is at rest (i.e., non-levitating), such that a radial centering function is inherently provided.
• Acryostat989, which may be substantially identical to those described above, is positioned in thecavity982. In particular, thecryostat989 contains one or more superconducting elements990 (which may in turn be formed of segments) that are mounted on aplatform983 that is in turn coupled viathermal link991 to a cooling source, which in view of the various versions described herein is merely shown in block form. Theentire cryostat989 is preferably coupled to a second motive device994, also shown in block form, that rotates it along with the superconducting element(s)990. It may also be coupled to a second motive device for moving it relative to an inner surface of thecavity982, such as in the vertical direction as shown inFIG. 26. As described above, in the case of non-cryogenic fluids, thecryostat989, or at least the portion housing the superconducting element(s)990 and any other cryogenic structures, is preferably evacuated or insulated to prevent thermal transfer to theadjacent vessel981.
• To form a magnetic coupling between the superconducting element(s)990 and thelevitation magnet988 of the pumping or mixingelement980, thecryostat989 is moved to a position within thecavity982 where these two structures are substantially aligned. In particular, the alignment is such that the superconducting element(s)990 face the adjacent levitation/driven magnet(s) on the pumping or mixingelement980, which of course is inside of thevessel981. Once this alignment is achieved, the superconducting element(s)990 are cooled to below the transition temperature (preferably less than 90K for a YBCO superconductor) in accordance with a field cooling protocol. As a result, a magnetic coupling is established with the levitation/drivenmagnet988 and the desired pinning forces are created that permit stable, exceptionally reliable levitation of the pumping or mixing element980 (and rotation, in the case where thesuperconducting clement990 is rotated, such as by using the configuration shown inFIG. 21).
• Once the magnetic coupling is formed, thecryostat989 may be moved further into thecavity982, either manually or using a third motive device996, such as a linear actuator or the like. As a result of the coupling formed between the superconducting element(s)990 and thelevitation magnet988, this causes thematching surface986 of the pumping or mixingelement980 to separate from the frusto-conical engagement surface984 (seeFIG. 27 and note action arrow Z). Rotation of thecryostat989 using the second motive device994 may then be effected as described above to cause the levitating pumping or mixingelement980 to rotate and, hence, pump or mix the fluid in thevessel981.
• To return the pumping or mixingelement980 to a resting position such that contact is re-established betweensurfaces984,986, the superconducting element(s)990 need only be returned to above the transition temperature, at which point the magnetic coupling is lost. To expedite this operation, and as described above, a heater998 may be used. Once the coupling is no longer formed, it should be appreciated that the pumping or mixingelement980 gently comes to rest such that thesurfaces984,986 are in engagement and the desired centering function is provided as a result of the matching tapers or slopes. Advantageously, this means that the user of the system need not have access to the pumping or mixingelement980 to ensure that it is properly centered for purposes of field cooling prior to levitation, and actually avoids the need for the use of a set-up kit, as described above (which in this case could be hat-shaped with a set-up or charging magnet corresponding in magnetic field and polarity to levitation magnet being placed over the head end of the cryostat989).
• The use of this “moving cryostat”' arrangement with the other embodiments of pumping or mixing systems disclosed herein is also possible, and in particular, with the embodiment shown inFIGS. 19,20,23-25 (which may require adjusting the relative dimensions or adding an annular piece of inert material to the pumping or mixing element to provide the matching surface986). Also, instead of forming the frusto-conical surface as part of thecavity982, it could actually be a separate, freestanding structure positioned at the same location or adjacent to the outer surface of the pumping or mixing element980 (see the phantom depiction ofengagement structure999 inFIG. 27), in which case the matchingsurface986 would be positioned accordingly (i.e., along the outer surface of the pumping or mixing element980). The entire arrangement could also be inverted (not shown), with theengagement surface984 being provided on the upper end of thecavity982 and thematching surface986 being on a corresponding surface of the pumping or mixing element980 (in which case, thecryostat989 would be withdrawn from thecavity982 once the desired magnetic coupling is formed). If thevessel981 is inverted, thecavity982 would preferably be elongated to avoid interfering with the adjacent wall of thevessel981.
• Each of the embodiments of pumping or mixing systems disclosed herein10,100,200,300,700,800, or900 could also be used for mixing a fluid with a product, such as a bacterial nutrient culture media, eukaryotic cell nutrient culture media, buffer, reagent, or like intermediate product for forming one or more end products. As a result of the levitating nature of the pumping or mixing element, application of these systems to vessels where the product and the pumping or mixing element are sealed in the vessel before use, including in an aseptic environment, is of course possible.
• In summary, a number ofsystems10,100,200,300,700,800,900 as well as variations on these systems and related methods, are disclosed that use or facilitate the use of superconducting technology to levitate a magnetic element that, when rotated, serves to pump or mix a fluid. In onesystem10, themagnetic element14 is placed in afluid vessel16 positioned external to acryostat12 having an outer wall orother housing18 for containing asuperconducting element20. A separate cooling source24 (either acryogenic chamber26,FIGS. 1 and 3 or arefrigerator48,FIG. 2) thermally linked to thesuperconducting element20 provides the necessary cooling to create the desired superconductive effects and induce levitation in themagnetic element14. Since the pumping or mixing element levitates in the fluid F, no penetration of the vessel walls by mixing or stirring rods is necessary, which eliminates the need for dynamic bearings or seals.
• Additionally, theouter wall18 of thecryostat12 or other housing defines achamber25 that thermally isolates and separates thesuperconducting element20 from thevessel16 containing the fluid F and pumping or mixingelement14. The thermal isolation may be provided by evacuating thechamber25, or filling it with an insulating material. By virtue of this thermal isolation and separation, thesuperconducting element20 can be positioned in close proximity to the outer wall orhousing18 adjacent to thevessel16 and pumping or mixingelement14, thereby achieving a significant reduction in the separation distance or gap G between the pumping or mixingelement14 and thesuperconducting element20. This enhances the magnetic stiffness and loading capacity of the magnetic levitating pumping or mixingelement14, thus making it suitable for use with viscous fluids or relatively large volumes of fluid.
• The exceptionally stable levitation provided as a result of the reduced separation distance also significantly reduces the potential for contact between the rotating pumping or mixing element and the bottom or sidewalls of the vessel. This makes this arrangement particularly well-suited for use in fluids that are sensitive to shear stress or the effects of frictional heating. However, since thesuperconducting element20 is substantially thermally isolated and separated from thevessel16, themagnetic element14, and hence the fluid F contained therein, may be shielded from the cold temperatures generated by the coolingsource24 to produce the desired superconductive effects and the resultant levitation. This allows for temperature sensitive fluids to be mixed or pumped. By using means external to thevessel16 to rotate and/or stabilize themagnetic element14 levitating in the fluid F, such as one or more rotating driving magnets coupled to themagnetic element14, the desired pumping or mixing action is provided.
• Additional embodiments of systems100 (900),200 for pumping or mixing a fluid wherein the necessary motive force is provided from the same side of the vessel at which the superconducting element is positioned are also disclosed, as aresystems300,400 for rotating an inline pumping or mixing element positioned in a vessel in the form of a pipe or the like in a similar fashion.Alternative systems700,800, and900 are also disclosed, which are particularly well adapted for applications using special vessels having cavities that assist in withstanding high internal pressures. Particular orientations of the crystallographic planes of the material used as the superconductor are also described to enhance the levitation force and magnetic stiffness of the coupling, which in turn increases the stability and load capacity of the pumping or mixing element, as is the use of opposing pairs of permanent magnets to provided a levitation-assist function. A manner of centering and setting up a pumping or mixing element in a hermetically sealed vessel is also disclosed.
• The foregoing description of various embodiments of the present invention have been presented for purposes of illustration and description. The description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. For example, while the use of a thermally separated superconducting element is disclosed, the subsequent development of room temperature superconductors would obviate this need. Instead of using a superconducting element as the motive device, another option is to use a separate drive structure (e.g., an electromagnetic coil) to form a coupling capable of transmitting torque to the particular fluid-agitating element (which may be “levitated” by a hydrodynamic bearing; see, e.g., U.S. Pat. No. 5,141,327 to Shiobara). The embodiments described provide the best illustration of the principles of the invention and its practical applications to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.

Claims (21)

1. A mixing apparatus comprising a flexible bag including an interior compartment for receiving a fluid, said bag including a cavity bounded by a wall projecting into the interior compartment, a mixing element in the interior compartment of the bag adjacent to the wall of the cavity, and a motive device adapted for insertion into the cavity for moving the mixing element.

2. The apparatus according toclaim 1, wherein the motive device comprises a rotating shaft.

3. The apparatus according toclaim 1, wherein the mixing element forms a non-contact coupling with the motive device.

4. The apparatus according toclaim 1, wherein the mixing element comprises at least one magnet.

5. The apparatus according toclaim 1, wherein the wall comprises a flexible sleeve.

6. The apparatus according toclaim 1, wherein the motive device is adapted to be electrically coupled to a power source.

7. The apparatus according toclaim 1, wherein the mixing element comprises at least one blade.

8. The apparatus according toclaim 1, further including a rigid container for supporting the bag.

9. The apparatus according toclaim 1, wherein a surface on the wall in the interior compartment is adapted for engaging a matching surface of the mixing element

10. A mixing apparatus, comprising: a container having a transparent sidewall at least partially defining an interior compartment for the mixing of media, said container including a cavity bounded by a wall projecting into the interior compartment, a mixing element in the container adjacent to the wall of the cavity, and a motive device for moving the mixing element.

11. The apparatus ofclaim 10, wherein the wall projects into the interior compartment from other than a floor of the container.

12. The apparatus ofclaim 10, wherein the wall projects into the interior compartment from an upper portion of the container.

13. The apparatus ofclaim 10, wherein the container comprises a flexible bag.

14. The apparatus ofclaim 10, wherein the mixing element comprises an opening for receiving the wall forming the cavity.

15. The apparatus ofclaim 14, wherein the mixing element comprises an inner surface adapted for engaging a surface of the wall.

16. A mixing apparatus comprising a container including an interior compartment for receiving a fluid, a mixing element in the interior compartment of the container and capable of spinning about an axis, and a tubular shaft projecting into the interior compartment and adapted for moving the mixing element, said tubular shaft including a cavity having a rigid rod positioned therein.

17. The mixing apparatus ofclaim 16, wherein the container comprises a flexible bag.

18. The apparatus ofclaim 16, wherein the tubular shaft comprises a flexible sleeve.

19. The apparatus ofclaim 16, wherein the tubular shaft is adapted to rotate relative to the flexible bag.

20. The apparatus ofclaim 16, further including a motor for rotating the tubular shaft.

21. The apparatus ofclaim 16, wherein the tubular shaft is associated with at least one bearing.

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