US20050186070A1

Movatterモバイル変換

Info

Publication number: US20050186070A1
Application number: US10/784,910
Authority: US
Inventors: Ling-Zhong Zeng; Richard Shelby; Michael Buckley
Original assignee: Revcor Inc
Current assignee: Revcor Inc
Priority date: 2004-02-23
Filing date: 2004-02-23
Publication date: 2005-08-25
Also published as: WO2005081979A3; WO2005081979A2

Abstract

The axial fan assembly according to some embodiments of the present invention has a shroud, a motor coupled to the shroud, and a fan coupled to the motor. By employing selected vane-to-blade ratios, blade twist angles, blade pitch angles, blade-to-shroud axial gaps, shroud solidities, vane swept angles, and vane inlet and outlet angles of specified amounts or falling within specified ranges, desirable fan performance is achieved. Any one or more of these parameters can be utilized alone or in combination with other parameters as desired.

Description

BACKGROUND OF THE INVENTION

Fans are used to generate air movement in a wide variety of applications, such as in heating, ventilating, and cooling systems. For example, a variety of axial-type fans (i.e., fans in which fluid is moved in a direction along the axis of rotation of the fan) are used in many industrial applications such as for ventilation purposes in office buildings, greenhouses, barns, factories, and other structures. Axial ventilation fans also have residential uses, such as in kitchens and bathrooms. As previously mentioned, axial fans are also commonly used in heating and cooling systems for heat transfer purposes. For example, axial fans are used for heat transfer purposes in a variety of applications, such as in air conditioning units, refrigeration units, computers, and in cars and other vehicles. In most of these applications, the fan is used to move air across a heat exchanger, wherein heat is transferred to the air as it passes by and/or through the heat exchanger.

Fan efficiency has become increasingly important, regardless of the type or application of the fan. Fan efficiency is typically important because fans are commonly driven by electric motors or other driving devices that consume valuable power. Inefficient fans consume more power, and are therefore less desirable than more efficient fans. Also, inefficient fans tend to require a different rotor geometry than efficient fans in order to meet the ventilation and heat transfer requirements of the systems in which the fans are used. For example, if a certain air flow is necessary for a system, an inefficient fan may have a greater number of blades, a greater diameter, and/or a larger motor than a more efficient fan. Therefore, inefficient fans can cost more than efficient fans in terms of materials and manufacturing expenses, and can occupy valuable system space. As such, fan manufacturers continue to search for ways to increase the efficiency of axial fans.

The marketplace, however, often places contradictory constraints upon fan manufacturers. For example, users of axial fans typically desire a relatively high fan efficiency, but also want fans that are compact and that generate the least noise possible. These constraints are often contradictory because many believe that fans generally need to be larger in order to reduce fan noise and/or airflow. Thus, in some cases, one demand can be met at the expense of another.

Axial fan efficiency is affected by a number of factors. For example, the efficiency of the motor or other device driving an axial fan can be an important factor in the overall efficiency of a axial fan and motor assembly. As another example, the speed of the fan motor and blades can impact fan efficiency. Increased fan motor and blade speed generally increases the amount of air turbulence moving through the fan—a result that is normally detrimental to fan efficiency. Turbulence is also a primary factor influencing the noise level of a fan.

The design and orientation of axial fan blades (e.g., axial fan blade shape, orientation with respect to the rest of the fan, and the like) are also factors in axial fan efficiency. It is generally recognized that certain shapes of fan blades are more efficient than others. For example, a machete or teardrop-shaped blade can often be more efficient that a cloverleaf-shaped blade.

The clearance between the blades of a fan and the fan housing can also impact axial fan efficiency. In many cases, this clearance is the distance between the tips of rotating blades and an adjacent fan housing wall. Blade-to-housing clearance is typically important because it often has a direct bearing upon the static pressure capabilities of the fan. For example, larger clearances between fan blade tips and adjacent housing walls can result in lower static pressure capabilities and lower fan efficiencies.

The design of an axial fan housing also impacts the efficiency of the axial fan. For example, the design of an fan housing air inlet can significantly influence efficiency of the axial fan by impacting the amount of turbulence within the fan. Turbulence within an axial fan can create a phenomenon known as vena contracta, which results in the reduction of the effective cross sectional area of the air inlet. Such a reduction permits less air to move through the air inlet, thereby reducing the efficiency of the axial fan.

Many of the efficiency factors discussed above are taken into account when designing conventional axial fans. However, still other efficiency factors can be important to axial fan performance, some of which are often not considered in conventional axial fan designs. Higher efficiency axial fans would be a welcome addition to the art.

SUMMARY OF THE INVENTION

Some embodiments of the present invention provide a fan assembly comprising a motor; a fan rotatably coupled to the motor for rotation about an axis and having a plurality of fan blades each having a leading edge with respect to a rotational direction of the fan blade and a trailing edge with respect to the rotational direction of the fan blade; and a shroud including a plurality of vanes extending transversely with respect to fluid flow through the fan assembly and through which fluid flows through the fan assembly, wherein the vanes are located downstream of the fan and oriented to extend away from a central area of the shroud, wherein each vane has a length defined between a radially inner end of the vane and a radially outer end of the vane, a leading edge, a trailing edge downstream of the leading edge of the vane with respect to fluid flow through the fan assembly, and a rearward swept angle defined between a first straight line extending through the radially inner and outer ends of the vane and a second straight line extending from the axis of the fan to the radially inner end of the vane, wherein the rearward swept angle is no less than about 5 degrees and is no greater than about 45 degrees, wherein each of the vanes is spaced from an adjacent vane by a gap measured from a first point on a first vane to a corresponding point on an adjacent vane, wherein each vane also has a chord length at the first point measured from the vane leading edge to the vane trailing edge, and wherein the fan assembly has a ratio of chord length to vane gap of no less than about 0.2 and no greater than about 3.5.

Also, some embodiments of the present invention provide a fan assembly comprising a motor; a fan rotatably coupled to the motor for rotation about an axis, wherein the fan has a plurality of fan blades each having a leading edge with respect to a rotational direction of the fan blade and a trailing edge with respect to the rotational direction of the fan blade; and a shroud including a plurality of vanes extending transversely with respect to fluid flow through the fan assembly and through which fluid flows through the fan assembly, wherein the vanes are located downstream of the fan and oriented to extend away from a central area of the shroud, wherein each vane has a length defined between a radially inner end of the vane and a radially outer end of the vane, a leading edge, a trailing edge downstream of the leading edge of the vane with respect to fluid flow through the fan assembly, and an inlet angle defined between a straight line tangent to the vane at the leading edge of the vane and a plane orthogonal to the axis of the fan, wherein the straight line lies in a plane tangent to an imaginary cylinder centered at the axis of the fan, wherein the inlet angle is no less than about 20 degrees and is no greater than about 70 degrees, wherein each of the vanes is spaced from an adjacent vane by a gap measured from a first point on a first vane to a corresponding point on an adjacent vane, wherein each vane also has a chord length at the first point measured from the vane leading edge to the vane trailing edge, and wherein the fan assembly has a ratio of chord length to vane gap of no less than about 0.2 and no greater than about 3.5.

In some embodiments, a fan assembly is provided, and comprises a motor; a fan rotatably coupled to the motor for rotation about an axis, wherein the fan has a plurality of fan blades each having a leading edge with respect to a rotational direction of the fan blade and a trailing edge with respect to the rotational direction of the fan blade; and a shroud including a plurality of vanes extending transversely with respect to fluid flow through the fan assembly and through which fluid flows through the fan assembly, wherein the vanes are located downstream of the fan and oriented to extend away from a central area of the shroud, wherein each vane has a length defined between a radially inner end of the vane and a radially outer end of the vane, a leading edge, a trailing edge downstream of the leading edge of the vane with respect to fluid flow through the fan assembly, and an outlet angle defined between a straight line tangent to the vane at the trailing edge of the vane and a line parallel to the axis of the fan, wherein the straight line lies in a plane tangent to an imaginary cylinder centered at the axis of the fan, wherein the outlet angle is no less than about 30 degrees in a direction counter to rotation of the fan and is no greater than about 30 degrees in a rotational direction of the fan; wherein each of the vanes is spaced from an adjacent vane by a gap measured from a first point on a first vane to a corresponding point on an adjacent vane, wherein each vane also has a chord length at the first point measured from the vane leading edge to the vane trailing edge, and wherein the fan assembly has a ratio of chord length to vane gap of no less than about 0.2 and no greater than about 3.5.

Some embodiments of the present invention provide a fan assembly, comprising a motor; a fan rotatably coupled to the motor for rotation about an axis, wherein the fan has a plurality of fan blades each having a leading edge with respect to a rotational direction of the fan blade and a trailing edge with respect to the rotational direction of the fan blade; and a shroud including a plurality of vanes extending transversely with respect to fluid flow through the fan assembly and through which fluid flows through the fan assembly, wherein the vanes are located downstream of the fan and oriented to extend away from a central area of the shroud, wherein each vane has a length defined between a radially inner end of the vane and a radially outer end of the vane, a leading edge, and a trailing edge downstream of the leading edge of the vane with respect to fluid flow through the fan assembly, wherein the shroud is separated from the fan by an axial gap between the leading edges of the vanes and the trailing edges of the fan blades, wherein the gap is no less than about 0.15 inches and no greater than about 1.5 inches, wherein each of the vanes is spaced from an adjacent vane by a gap measured from a first point on a first vane to a corresponding point on an adjacent vane, wherein each vane also having a chord length at the first point measured from the vane leading edge to the vane trailing edge, and wherein the fan assembly also has a ratio of chord length to vane gap of no less than about 0.2 and no greater than about 3.5.

In additional embodiments of the present invention, a fan assembly is provided, and comprises a motor; a fan rotatably coupled to the motor for rotation about an axis, wherein the fan has a plurality of fan blades each having a leading edge with respect to a rotational direction of the fan blade and a trailing edge with respect to the rotational direction of the fan blade; and a shroud including a plurality of vanes extending transversely with respect to fluid flow through the fan assembly and through which fluid flows through the fan assembly, wherein the vanes are located downstream of the fan and oriented to extend away from a central area of the shroud, wherein each vane has a leading edge and a trailing edge downstream of the leading edge with respect to fluid flow through the fan assembly, wherein each of the vanes is spaced from an adjacent vane by a gap measured from a first point on a first vane to a corresponding point on an adjacent vane, wherein each vane also has a chord length at the first point measured from the vane leading edge to the vane trailing edge, and wherein the fan assembly has a ratio of chord length to vane gap of no less than about 0.2 and no greater than about 2.5.

Further objects and advantages of the present invention, together with the organization and operation thereof, will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described with reference to the accompanying drawings, which show an exemplary embodiment of the present invention. However, it should be noted that the invention as disclosed in the accompanying drawings is illustrated by way of example only. The various elements and combinations of elements described below and illustrated in the drawings can be arranged and organized differently to result in embodiments which are still within the spirit and scope of the present invention.

In the drawings, wherein like reference numeral indicate like parts:

FIG. 1A is a cross-sectioned elevational view of a fan assembly of the present invention, shown mounted near a heat exchanger;

FIG. 1B is a cross-sectioned elevational view of the fan assembly of the present invention illustrated inFIG. 1A, shown mounted in an alternate configuration;

FIG. 2 is an exploded view of the fan assembly illustrated inFIGS. 1A and 1B;

FIG. 3 is a perspective view of the fan assembly illustrated inFIGS. 1A, 1B, and2, shown partially sectioned;

FIG. 4 is a plan view of the fan assembly illustrated inFIGS. 1A, 1B,2 and3, viewed from the shroud side of the fan assembly;

FIG. 5 is a side cross-sectional view of the fan assembly illustrated inFIGS. 1-4, taken alonglines5—5 ofFIG. 4;

FIG. 6 is a plan view of the fan assembly illustrated inFIGS. 1-5, viewed from the fan side of the assembly;

FIG. 7 is a detail cross-sectional side view of part of the fan assembly illustrated inFIGS. 1-6, taken along lines7—7 ofFIG. 4;

FIG. 8 is an enlarged view of the cross-sectioned elements illustrated inFIG. 7;

FIG. 9 is an end view of a fan blade from the fan assembly illustrated inFIGS. 1-8; and

FIGS. 10A-10C are performance curve comparison charts showing the performance of the fan assembly illustrated inFIGS. 1-9 compared to two conventional axial fans.

DETAILED DESCRIPTION OF EMBODIMENTS

An exemplary embodiment of an axialflow fan assembly10 according to the present invention is illustrated inFIGS. 1-10. Theexemplary fan assembly10 inFIGS. 1-10 has ashroud14, amotor42 coupled to theshroud14, and afan50 coupled to themotor42. In operation, themotor42 rotates adrive shaft46 coupled to thefan50. As thedrive shaft46 rotates, it powers thefan50 to rotate within theshroud14, and generates air movement.FIGS. 1A and 1B illustrate the fan in an exemplary environment. As illustrated, the fan is mounted to generate a stream of air to remove heat from condensing coils. This is just one of the many possible uses of this fan. Although a heat exchange environment is described herein and illustrated inFIGS. 1A and 1B, the fan of the present invention can be employed in any air moving application. Other uses known by those having ordinary skill in the art fall within the spirit and scope of the present invention.

As illustrated inFIGS. 2-6, the illustratedshroud14 at least partially enclosesfan blades58 extending from ahub54 of thefan50. A portion of theshroud14 has a generallycircular wall17 that extends around the radial periphery of thefan50, although shrouds having any other wall shape can instead be employed as desired. The generally circular shapedwall17 illustrated inFIGS. 2-6 (often referred to as a fan cylinder or fan ring) can have any diameter desired, depending at least in part upon the size of the fan employed. In some embodiments, the fan assembly has a nominal size between six inches and eighteen inches. However, other sized fans also fall within the spirit and scope of the present invention.

Thefan shroud14 in the illustrated exemplary embodiment has a set of mountingbosses15 that can be employed to mount thefan assembly10 to a frame, housing, or other structure. Any number of mounting bosses having any shape can be employed, such as tab-shaped protrusions extending from thewall17 of theshroud14 as shown in the figures, lugs, posts, or fingers extending from thewall17, a rib or flange extending partially or fully around thewall17, and the like. Such mounting elements or features can be secured to a frame, housing, or other structure by bolts, screws, nails, rivets, pins, or other conventional fasteners, by clamps, clips, inter-engaging or snap-fit fingers or other features, and the like.

In some embodiments, thesame fan assembly10 can be mounted in different orientations as needed in different applications. For example, it may be desirable to mount thefan assembly10 in one orientation in order to pull air through a condenser or other device, while in another application is may be desirable to mount the fan in a reversed direction to blow air into a condenser or other device. This mounting versatility is provided in some embodiments by the use of twodifferent shrouds14, each of which has mounting elements or features (described above) located at different axial positions on theshroud14. In the illustrated embodiment for example, oneshroud14 has mountingbosses15 located at a downstream end of the fan assembly10 (seeFIG. 1A), while anothershroud14′ has mountingbosses15′ located at an upstream end of the fan assembly10 (seeFIG. 1B). In this manner, a

shroud

14,14′ can be selected that will enable at least the majority of thefan assembly10 to be recessed within the structure to which it is mounted.

In other embodiments, the mounting elements or features of theshroud14 can be located in any axial position along theshroud14. By way of example only, mountingbosses15 can be located at an axial mid-point between the ends of theshroud14, thereby permitting thefan assembly10 to be mounted in both orientations described above without the need for two different shrouds and while still keeping a substantial portion of thefan assembly10 recessed within the structure to which it is mounted in both orientations. Regardless of the axial location of the mounting elements or features employed on theshroud14, thefan assembly10 can still be mounted in two opposite orientations (although the ability to recess a majority or the entirety of thefan assembly10 in both orientations may be limited).

The mounting elements or features15 of theshroud14 described above can be integral with theshroud14. However, in other embodiments these mounting elements or features15 are attached to theshroud14 in any suitable manner, such as by a ring (not shown) encircling theshroud14 and that can be secured with respect to theshroud14 in a number of different axial positions. As another example, the mounting elements or features15 can be attached to theshroud14 at different axial locations by screws, bolts, nails, rivets, pins, or other conventional fasteners, inter-engaging elements, adhesive or cohesive bonding material, and the like.

The size of thefan ring17 with respect to thefan50 can have an impact on the efficiency of thefan assembly10. As will be described in greater detail below, the efficiency of thefan assembly10 can increase as the spacing between thefan50 and thefan ring17 decreases. Thus, in some embodiments of the present invention, thefan ring17 generally has an inside diameter nearly matching the outside diameter of thefan50. More specifically, in some embodiments good performance results are achieved by using afan ring17 having an inside diameter providing a non-contacting clearance fit with thefan blades58 or a clearance not exceeding 0.125 inches. A clearance between thefan blades58 and thefan ring17 of no greater than 0.08 can provide better performance results. Also, a clearance between thefan blades58 and thefan ring17 not exceeding 0.05 inches can provide still better performance results.

As seen inFIG. 3, thefan cylinder17 can have a double wall. Although a single-walled fan cylinder17 can be employed, a double wall fan cylinder can reduce vibration generated by operation of thefan assembly10.

Theshroud14 in the illustrated exemplary embodiment has a plurality ofvanes18 directly or indirectly attached to thefan cylinder17 at one end of thefan cylinder17. Although thevanes18 can be integral with thefan cylinder17 as shown inFIGS. 2-5, in other embodiments thevanes18 are not integral with thecylinder17, and can be attached to the cylinder in any conventional manner. Furthermore, even though thevanes18 of the illustrated embodiment are located at one end or at the edge of thecylinder17, thevanes18 do not necessarily need to be located at an end or edge of thecylinder17. For example, depending upon the shape and length of thefan cylinder17, thevanes18 could be located in different axial positions along thefan cylinder17. The plurality ofvanes18 can serve several functions. For example, thevanes18 can do one or more of the following: help to increase performance of thefan assembly10, alter the direction of air movement through thefan assembly10, and/or act as a safety device (to limit or prevent access to thefan50 through the shroud14). As shown in the illustrated embodiment, thevanes18 can extend in generally radial directions from thefan cylinder17 towards the center of theshroud14. Thevanes18, however, do not necessarily have to extend directly radially. Rather, in alternative embodiments, thevanes18 can have any orientation with respect to theshroud14, including but not limited to orientations in which thevanes18 are parallel to radial lines extending from an axis of rotation of thefan50, orientations in which the vanes are at an angle with respect to such radial lines (e.g., wherein the radially innermost portion of eachvane18 is located in front of or behind the radially outermost portion of eachvane18 in the circumferential direction), orientations in which imaginary lines drawn through the length of thevanes18 intersect an axis of rotation of thefan50, orientations in which such imaginary lines do not intersect the axis of rotation of thefan50, and the like.

Thevanes18 of theshroud14 can be arranged on theshroud14 in any desired manner. By way of example only, thevanes18 can be equally spaced from one another, can be arranged in any pattern desired (i.e., repeating or non-repeating pattern), or can be randomly spaced. In the illustrated exemplary embodiment, thevanes18 extend in a generally radial direction and are also angled with respect to the direction of fan rotation. More specifically, the radially innermost end of eachvane18 illustrated in the figures is located circumferentially ahead of the radially outermost end of the vane18 (with reference to the direction of rotation of the fan50). As explained above, thevanes18 can instead be oriented in an opposite direction, in which case the radially innermost end of eachvane18 is located circumferentially behind the radially outermost end of thevane18.

If employed,vanes18 can be located on all or any portion of theshroud14, including thefan cylinder17. As shown in the illustrated embodiment,vanes18 cover the majority of theshroud14 surface perpendicular to the axis of rotation of thefan50. However, as illustrated, thevanes18 extend only partially between thefan cylinder17 and the center of thefan cylinder17. In the illustrated embodiment of the present invention,vanes18 extend across the same general area in front of the fan50 (downstream of the fan50) as thefan blades58. The remainder of the center portion of theshroud14, as seen inFIGS. 2 and 3, can serve to house themotor42 as shown in the figures. Therefore, in some embodiments of the present invention,vanes18 are not included in this area of theshroud14. However, in some embodiments,vanes18 can be placed in this area, depending at least in part upon the axial position of themotor42 with respect to theshroud14.

Regardless of the number and orientation of thevanes18, thevanes18 can take any cross-sectional shape desired. For example, eachvane18 can be flat, triangular, U-shaped, can have a generally airfoil shape, can present a concave or convex shape toward or away from the direction of rotation of theblades58 and/or in either direction along the axis of rotation of thefan50, and the like. Furthermore, thevanes18 can be cambered between thevane leading edges30 andvane trailing edges34 and/or can be twisted along the length of the vanes (in a clockwise or counterclockwise direction viewed along the length of the blade from tip to root), or the like. As best illustrated inFIG. 8,vanes18 of the illustrated embodiments have a cambered, generally airfoil-like cross-section, wherein the concave portion of thecambered vanes18 faces the leading edge of theblades58. In addition, thevanes18 can have any shape desired along the length of thevanes18. In the illustrated embodiment, thevanes18 are substantially straight along the length of thevanes18. However, in other embodiments for example, thevanes18 can be bowed in either direction with respect to the direction of rotation of thefan50.

In some embodiments of the present invention, the orientation of the leading and trailing edges of the vanes can significantly influence the performance of thefan assembly10. With reference toFIG. 8, the orientation of the leadingedge30 of eachvane18 can be defined at least in part by an angle D between a plane orthogonal to the axis of rotation of thefan assembly10 and a line tangent to the surface of thevane18 facing (or at least partially facing) thefan blades58 at theleading edge30 of thevane18. As discussed herein, the shape and/or orientation of thevanes18 can change along the lengths of thevanes18. Accordingly, in some embodiments, this leading edge or “inlet” angle D is measured at a mid-point along the lengths of thevanes18, or at (½R) or (⅔R) in other embodiments (where R is the radius of thefan assembly10 at the outer limits of the vanes18).

Iri some embodiments, this leading edge or “inlet” angle D of thevanes18 is at least 20° and/or is no greater than 70°. Better performance results can be achieved by employing an angle D that is at least 30° and/or is no greater than 60°. Still better performance can be achieved by employing an angle D that is at least 45° and/or is no greater than 55°. These ranges are generally applicable to fans having a nominal size from about six inches to about eighteen inches, although such vane inlet angles D can be employed in fan assemblies having any diameter. Depending upon other parameters on thefan assembly10, such as the type and characteristics of the fluid being moved, the normal operational speed (or anticipated ranges of speeds) of thefan assembly10, and the like, the vane inlet angle D can vary.

In some embodiments of the present invention, the vane inlet angles (or ranges of vane inlet angles) described above are employed alone or in combination with other characteristics of thefan assembly10 described herein to generate superior fan performance. With continued reference toFIG. 8, the orientation of the trailingedge34 of eachvane18 can be defined at least in part by an angle E between a plane parallel to and passing through the axis of rotation of thefan assembly10 and a line tangent to the surface of thevane18 facing (or at least partially facing) thefan blades58 at the trailingedge34 of thevane18. As discussed herein, the shape and/or orientation of thevanes18 can change along the lengths of thevanes18. Accordingly, in some embodiments, this trailing edge or “outlet” angle E is measured at a mid-point along the lengths of thevanes18, or at (½R) or (⅔R) in other embodiments (where R is the radius of thefan assembly10 at the outer limits of the vanes18).

In some embodiments, this trailing edge or “outlet” angle E of thevanes18 is at least −30° and/or is no greater than 30° (wherein a negative angle refers to an angle in a direction opposite the direction of rotation of thefan50 as viewed inFIG. 8, and wherein a positive angle refers to an angle in the direction of rotation of thefan50 as also viewed inFIG. 8). However, an angle E of at least −10° and/or no greater than 20° can provide better performance results. Also, an angle E of at least −5° and/or no greater than 10° can provide still better fan performance. These ranges are generally applicable to fans having a nominal size from about six inches to about eighteen inches, although such vane outlet angles E can be employed in fan assemblies having any diameter. Depending upon other parameters on thefan assembly10, such as the type and characteristics of the fluid being moved, the normal operational speed (or anticipated ranges of speeds) of thefan assembly10, and the like, the vane outlet angle E can vary.

In some embodiments of the present invention, the vane outlet angles (or ranges of vane outlet angles) described above are employed alone or in combination with other characteristics of thefan assembly10 described herein to generate superior fan performance.

In some embodiments of the present invention, selected rearwardly-swept angles or ranges of angles of the vanes18 (when viewed along the axis of rotation of the fan assembly10) are employed alone or in combination with other characteristics of thefan assembly10 described herein to generate superior fan performance. Avane18 is said to be rearwardly-swept when a radially outermost end of thevane18 is located circumferentially behind a radially innermost end with reference to the direction of rotation of thefan50. A rearwardly-sweptvane18 can be defined by an angle between a line extending along the leading or trailing

edge

34,30 of thevane18 and a straight line extending from the axis of rotation of thefan assembly10 through a radially innermost point on thevane18. In other embodiments (such as those embodiments in which thevane18 is not straight along the length of the vane18), the amount which avane18 is rearwardly-swept can be defined by an angle between the chord of the vane18 (or, if no chord can be readily identified, a straight line extending through the radially innermost and outermost points of the vane18) and a straight line extending from the axis of rotation of thefan assembly10 through the radially innermost point of thevane18. All measurements of the angle defining the rearward sweep of the vane18 (referenced herein and in the appended claims) are made with reference to a plan view of thefan assembly10 such as that shown inFIGS. 4 and 6.

In some embodiments of the present invention, this rearward sweep angle of thevanes18 is no less than 5° and/or is no greater than 45°. However, better performance results can be achieved by employing a rearward sweep angle that is less than 10° and/or is no greater than 35°. Also, a rearward sweep angle that is less than 10° and/or is no greater than 25° can produce still better fan performance. These ranges are generally applicable to fans having a nominal size from about six inches to about eighteen inches. However, these ranges are not limited to fans of such size. Depending upon other parameters on thefan assembly10, such as the type and characteristics of the fluid being moved, the normal operational speed (or anticipated ranges of speeds) of thefan50, and the like, this angle can vary.

As illustrated inFIGS. 2-6, the vaned area of theshroud14 can be split into two radial areas—one area for radiallyouter vanes22 and the other area for radiallyinner vanes26. In some embodiments, dividing the vaned area into two

areas

22,26 can improve performance of thefan assembly10 and/or can provide greater structural strength to theshroud14. Since pressure gradients can occur across the length of thefan blades58, in some cases the performance of thefan assembly10 can be improved by selecting the number ofvanes18 in both the outer22 and inner26 vane areas based upon desired operational characteristics of the fan assembly10 (e.g., fan speed, fan power, and the like). For example, in the illustrated embodiment, thirty-sevenouter vanes22 and twenty-oneinner vanes26 are used to achieve good fan performance under certain conditions. However, in various other operating conditions (i.e., for different fan speeds and diameters, when moving different fluids having different properties, for fans having different fan blade shapes, and the like), the number of vane areas and the vane count within those areas can be altered as desired. For example, in some embodiments, theinner vanes26 and theouter vanes22 are integral. In other words, theouter vanes22 can extend all the way to the central hub (if employed). Additionally, in yet other embodiments, the inner vanes can be omitted, leaving a ring-shaped gap between a motor housing wall53 (if employed) of theshroud14 and the outermost tier ofvanes22, in which case struts or other structural members can secure themotor housing wall53 to the rest of theshroud14. Furthermore, in some embodiments, additional tiers of vanes can be employed (i.e., inner, outer, and middle; first, second, third, etc.).

The vanes located in various tiers need not necessarily have the same characteristics as vanes located in other tiers. For example, theinner vanes26 in the illustrated embodiment can have the same or different cross-sectional shapes as theouter vanes22, and can have any shape described above. By way of example only, theinner vanes26 in the illustrated embodiment can have a first shape, while theouter vanes22 can have a second shape different from the first. Additionally, the different tiers of vanes can be oriented in any manner described above. Thus, theinner vanes26 can have first orientation, while theouter vanes22 can have a second orientation different than the first.

In some embodiments, the number of vanes in each tier can be the same. However, in other embodiments, the number of vanes in each tier can be different. In some embodiments, the blade-to-vane count is about 10:50 (e.g., in some 11-inch diameter fans according to the present invention). However, regardless of the number of vaned areas or tiers employed (i.e., the number of areas of theshroud14 having different sets of vanes18), it is desirable in some embodiments to employ a number of vanes that is not a multiple of the blade count. When the vane count is a multiple of the blade count, harmonics can be more likely to develop, causing pressure problems within thefan50 and resulting performance reductions of thefan assembly10. For example, if thefan50 were to have a blade count of tenblades58, then in some embodiments none of the vanes areas (if there is more than one) would have a vane count equal to a multiple of ten, such as twenty, thirty, forty, fifty, sixty, etc. In some embodiments, the blade-to-vane count is about 10:65 (e.g., in some 12-inch diameter fans according to the present invention).

In some embodiments of the present invention, superior performance results can be obtained by employing a particular shroud solidity or by employing any shroud solidity within a range of shroud solidities. In such embodiments, selected shroud solidities (or ranges of shroud solidities) are employed alone or in combination with other characteristics of thefan assembly10 described herein to generate superior fan performance. Shroud solidity is a characteristic of theoverall fan assembly10 that can be selected to change the efficiency of thefan assembly10. Referring toFIGS. 7 and 8, the solidity of the shroud is the ratio of a vane's chord length (indicated as “A”) to the gap (indicated as “B”) measured between the same point on two adjacent vanes. For example, in the illustrated embodiment, the measurement for shroud solidity is made from the midpoint of the trailingedge34 of afirst vane18 to the midpoint of the trailingedge34 of anadjacent vane18. In other embodiments, this measurement can be made at theleading edges30 of thevanes18 or anywhere between the leading and trailing

edges

30,34 of thevanes18. Note, however, that since thevanes18 can be arranged in a radial fashion, the gap betweenvanes18 can vary along the radial length of thevanes18. Thus, the measurement of shroud solidity as described above can vary along thevanes18. The chord length is measured along a line from the leadingedge30 to the trailingedge34 of the vane.

With continued reference to the measurement of shroud solidity described above, in some embodiments, the chord length of thevanes18 is variable along the length of the vane from root to tip. Thus, the chord length of thevanes18 used to measure shroud solidity is measured at the same location used to measure the gap betweenadjacent vanes18 as described above (both measurements being made at the same location anywhere along the length of the vanes18). In the illustrated embodiment, for example, the gap and chord length measurements of thevanes18 are taken at the same point: at the midpoint of theouter vanes22. In other words, the either or both measurements can be taken at a radial mid-point in the outer two-thirds of thefan assembly10. As discussed above, either or both measurements can be taken elsewhere in other embodiments, such as anywhere along theouter vanes22 in the illustrated exemplary embodiment, at a location half way between the axis of rotation and the radially outermost ends of thevanes18, at a location half way between the radially innermost and radially outermost ends of thevanes18, and the like.

The solidity of theshroud14 in some embodiments of the present invention is at least 0.2 and/or is no greater than 3.5 (e.g., measured at the vane trailing edges and at a midpoint along the vanes of the shroud, such as at the midpoint of theouter vanes22 in the illustrated embodiment).

However, a shroud solidity of at least 0.5 and/or no greater than 2.5 can produce better performance results. Also, still better performance results can be achieved by employing a shroud solidity of at least 1.0 and/or no greater than 2.0. These ranges are generally applicable to fans having a nominal size from about six inches to about eighteen inches. However, these ranges are not limited to fans of such size. In still other embodiments of the present invention, the above-described solidity ranges are different, often depending at least in part upon other parameters on thefan assembly10, such as the number ofblades58 of thefan50, the distance of thefan50 from theshroud14, the normal operational speed (or anticipated ranges of speeds) of thefan50, and the like.

As shown in the illustrated exemplary embodiment, amotor42 is used to power thefan assembly10. Themotor42 of thefan assembly10 can be anyconventional motor42, such as an AC or DC electric motor (by way of example only, a permanent split capacitor AC induction motor or a brushless DC motor). Some embodiments of the present invention utilize ahigh efficiency motor42 to help reduce overall system inefficiencies. In some embodiments such as that shown in the figures, themotor42 has amotor housing38 secured to theshroud14. Themotor42 can instead be attached to theshroud14 by one or more brackets connected to themotor42 andshroud14, by mounting lugs on themotor42 and/orshroud14, and the like. In the illustrated exemplary embodiment, themotor housing38 is attached to theshroud14 through the use of conventional fasteners, such as screws, nuts and bolts, rivets, pins or other conventional fasteners, by snap fit connections, adhesive or cohesive bonding material, press fits, and the like.

With continued reference to the illustrated embodiment, themotor42 mounted on theshroud14 has adrive shaft46 that extends through themotor housing38 to drive thefan50. As shown inFIGS. 3 and 5, thedrive shaft46 of themotor42 can be attached to ahub54 of thefan50. This attachment can be any conventional type of attachment, such as a keyed connection, a press or interference fit, a splined connection, or any other male/female connection (whether or not secured by a set screw, pin, or other such element), a coupling connection, and the like. In those embodiments of the present invention in which thefan50 employs ahub54, a plurality offan blades58 can be attached at the hub's periphery (or can be integral to the hub54) and can extend radially outward therefrom. In other embodiments, thefan blades58 extend out from any other rotating central element to which thefan blades58 are attached or with which thefan blades58 are integral. Thus, rotation of themotor42 causes thedrive shaft46 to rotate, which in turn causes thecentral hub54 to rotate (if employed) and causes the plurality offan blades58 to rotate.

In the illustrated embodiment of the present invention, thehub54 has afirst face55 that extends in a generally radial direction and which is generally perpendicular to thedrive shaft46. Thisfirst face55 can be circular in shape with the drive shaft coupling to this face substantially at the center of the circle. In other embodiments, the portion to which thedrive shaft46 couples can have any shape desired, including without limitation afirst face55 that is concave or convex in the direction away from the fan assembly10 (e.g., whether having a rounded profile in either direction, a profile defined by planar surfaces joined at angles with respect to one another, and the like). In other embodiments, the forward end of thehub54 is pointed or otherwise protrudes along the axis of rotation of thefan assembly10. Other hub shapes54 can be employed in still other embodiments of the present invention. With reference back to the illustrated exemplary embodiment, asecond face56 of the illustratedhub54 extends from the periphery of thefirst face55 towards theshroud17, and can be joined directly to thefirst face55 or can be joined thereto by a curved or angled intermediate surface as shown in the figures. In the illustrated embodiment, thissecond face56 wraps around and partially encloses a portion of themotor housing38. As illustrated, thehub54 in cooperation with theshroud14 can substantially enclose themotor housing38. In some embodiments, themotor42 can be entirely enclosed or encased by thehub54 andshroud17 with the exception of a gap sufficient (or only sufficient) to provide rotational clearance between thehub54 andshroud14.

Theblades58 of thefan50 can be attached to or integral with thehub54 along thesecond surface56 as shown in the figures. In other embodiments, the blades extend from other portions of the hub determined at least in part upon the shape of thehub54 employed. Eachblade58 has aroot62 and atip66. Theblades58 are coupled to or are integral with thehub54 at theroot62, with the remainder of theblade58 extending at least radially therefrom to thetip66. Theblades58 can have any shape desired, such as a cloverleaf, machete, or teardrop shape by way of example only. In addition, the shape of theblades58 can change along their length (fromroot62 to tip66). By way of example only, the shape of eachblade58 illustrated in the figures tapers fromroot62 to tip66. Thistapered blade58 can provide significant performance enhancements to thefan assembly10 of the present invention. In other embodiments,non-tapered blades58 can instead be employed.

Theblades58 can have any cross-sectional shape desired, including without limitation rectangular, flat, triangular, irregular, and other cross-sectional shapes. In the illustrated embodiment for example, thefan blades58 each have a generally airfoil-shaped cross-section as best shown inFIG. 7. Referring toFIG. 7, the thicker portion of the illustrated airfoil (including the thick edge) is generally referred to as the leadingedge70 of theblade58 because during normal rotation of thefan50 it is rotationally ahead of the remainder of theblade58. Conversely, the thinner portion of the blade (including the thin edge) is generally referred to as the trailingedge74 because during normal rotation of thefan50 it is rotationally behind the remainder of theblade58. However, determination of the leadingedge70 and trailingedge74 for ablade58 is dependent upon the direction of rotation of thefan50. Therefore, note that in the description which follows, terms such as “forward,” “backward,” “leading” and “trailing” are all with respect to the direction of rotation of thefan assembly10 indicated inFIG. 6. It is apparent that if thefan50 were to rotate in the opposite direction, then these terms would be reversed (i.e., “forward” would become “backward” and “leading” would become “trailing”).

Referring toFIGS. 7 and 9, it is shown that the leadingedge70 of eachblade58 is displaced axially with respect to the trailingedge74. This is sometimes referred to as the pitch angle of theblade58 or the angle of attack. With reference to the direction of airflow through the fan assembly10 (in a generally axial direction) past thevanes18 andblades58, the leadingedge70 of eachblade58 is located upstream of the trailingedge74, or is angled below a horizontal line drawn at the trailingedge74 of theblade58 inFIG. 7 (wherein theblade58 rotates to the left inFIG. 7 in normal operation). Although eachblade58 can instead be angled such that the leadingedge70 is instead located downstream of the trailingedge74, or such that the leading and trailing

edges

70,74 are at the same axial location in thefan assembly10, good performance results are achieved by the blades in which the leadingedge70 of eachblade58 is located upstream of the trailingedge74. A pitch angle of at least 10 degrees and/or no greater than 35 degrees at a midpoint along the length of eachblade58 can provide good performance results. However, a pitch angle of at least 12 degrees and/or no greater than 30 degrees at a midpoint along the length of eachblade58 can provide better performance results. Also, a pitch angle of at least 15 degrees and/or no greater than 23 degrees at a midpoint along the length of eachblade58 can provide still better performance results.

In some embodiments of the present invention, it is the angle of blade pitch that helps determine the amount of airflow and the pressure differential across the airfoil. In some embodiments, the pitch angle of eachblade58 varies radially. Stated another way, each blade's angle of attack is different at theroot62 than it is at thetip66. This characteristic can be referred to as blade twist. In some embodiments of the present invention, selected blade twist angles (or ranges of blade twist angles) are employed alone or in combination with other characteristics of thefan assembly10 described herein to generate superior fan performance.FIG. 9 illustrates blade twist and a convenient method of measuring the blade twist angle. To measure the blade twist angle as illustrated, a chord is drawn along thetip66 of theblade58 from the trailingedge74 to the leadingedge70. Then, a second chord is drawn at theroot62 of theblade58 from the trailingedge74 to the leadingedge70. The angle between the two chords is the blade twist angle. Any (or no) amount of blade twist can be employed in the present invention. In some embodiments, a blade twist angle falling between 0° and 45° can employed for good performance results. However, a blade twist angle falling between 5° and 25° can be employed for better fan performance. Also, a blade twist angle falling between 8° and 18° can be employed for still better fan performance. Depending upon other parameters on thefan assembly10, such as the type and characteristics of the fluid being moved, the normal operational speed (or anticipated ranges of speeds) of thefan50, and the like, the blade twist angle can vary.

In some embodiments of the present invention, thefan blades58 extend radially toward positions immediately adjacent thefan cylinder17 of theshroud14, wherein clearance exists (and in some cases, only sufficient clearance exists) for rotation of thefan blades58 with respect to theshroud14. The position of thefan blades58 with regard to theshroud14 can have an effect on the efficiency and performance of thefan assembly10. For example, the clearance between thetips66 of theblades58 and the inside wall of thefan cylinder17 as just described can be an important parameter relating to the efficiency and performance of thefan assembly10. If close tip clearance is not maintained, leakage can occur between thefan blade tips66 and theshroud14 because air will take the path of least resistance through thefan assembly10, thereby generating reduced performance in regard to pressure capabilities and airflow.

In some embodiments of the present invention, another parameter that can influence performance of thefan assembly10 is the spacing between thevanes18 on theshroud14 and theblades58 of thefan50. In those embodiments in which the portions of thefan blades58 andvanes18 closest to one another are the trailingedges74 of thefan blades58 and theleading edges30 of the vanes18 (as discussed above), this spacing is measured between the trailingedges74 of thefan blades58 and theleading edges30 of thevanes18. However, in other embodiments in which the pitch of thefan blades58 is different and/or in which the orientation of thevanes18 is different, this spacing is measured between the closest portions of thefan blades58 andvanes18. In some embodiments of the present invention, selected vane-to-blade spacings (or ranges of vane-to-shroud spacings) are employed alone or in combination with other characteristics of thefan assembly10 described herein to generate superior fan performance. With reference to the illustrated exemplary embodiment,FIGS. 7 and 8 provide a cross-sectional view of the proximity of thefan blades58 to thevanes18 on theshroud14. In some embodiments, the gap between the trailingedges74 of thefan blades58 and theleading edges30 of thevanes18, as indicated by the letter C, is at least 0.15 inches and/or is no greater than 1.5 inches. However, this gap can be at least 0.2 inches and/or no greater than 1.0 inches for better performance results. Also, this gap can be at least 0.25 inches and/or no greater than 0.5 inches for still better fan performance. These ranges are generally applicable to fans having a nominal size from about six inches to about eighteen inches, although such gaps can be employed in fan assemblies having any diameter. Depending upon other parameters on thefan assembly10, such as the type and characteristics of the fluid being moved, the normal operational speed (or anticipated ranges of speeds) of thefan50, and the like, the gap between thefan blades58 and thevanes18 can vary.

In some embodiments of the present invention, significant performance improvements are achieved over conventional fan assemblies when one or more of the fan assembly characteristics is employed as discussed above. By way of example only, the performance of the illustratedfan assembly10 having a nominal diameter of twelve inches is illustrated inFIGS. 10A-10C and compared to two conventional twelve inch fans. Thefan assembly10 illustrated in the figures has a blade twist angle of approximately 11°, a solidity ratio of approximately 1.5 (measured at a mid-point along the lengths of the outer vanes22), a gap betweenblade trailing edges74 and vane leading edges of approximately 0.38 inches, a vane inlet angle D of approximately 51° (measured at a mid-point along the lengths of the outer vanes22), a vane outlet angle E of approximately 4° (measured at a mid-point along the lengths of the outer vanes22), a leading edge rearwardly-swept angle of approximately 16° and a blade pitch angle of approximately 19° (measured at a mid-point along the lengths of the outer vanes22). The first conventional fan used to create the comparison inFIGS. 10A-10C is an twelve inch fan currently available in the marketplace. This fan is labeled as Prior Art Fan No. 1 onFIGS. 10A-10C. The second conventional fan used in the caparison is another twelve inch fan currently available in the marketplace. This fan is labeled as Prior Art Fan No. 2 onFIGS. 10A-10C.

The characteristic curve plots inFIGS. 10A-10C illustrate the total efficiency, the brake horsepower, and the static pressure of each fan assembly against air flow. These numbers were obtained experimentally by measuring and calculating the parameters at various air flows amounts.

The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention. For example, one or more of the above mentioned embodiments can be applied to an axial fan individually or in combination to increase the efficiency of the fan as desired.

Claims

1. A fan assembly, comprising:

a motor;

a fan rotatably coupled to the motor for rotation about an axis, the fan having a plurality of fan blades, each fan blade having a leading edge with respect to a rotational direction of the fan blade and a trailing edge with respect to the rotational direction of the fan blade; and

a shroud including a plurality of vanes extending transversely with respect to fluid flow through the fan assembly and through which fluid flows through the fan assembly, the vanes being located downstream of the fan and oriented to extend away from a central area of the shroud; each vane having:

a length defined between a radially inner end of the vane and a radially outer end of the vane;

a leading edge;

a trailing edge downstream of the leading edge of the vane with respect to fluid flow through the fan assembly; and

a rearward swept angle defined between a first straight line extending through the radially inner and outer ends of the vane and a second straight line extending from the axis of the fan to the radially inner end of the vane, wherein the rearward swept angle is no less than about 5 degrees and is no greater than about 45 degrees;

wherein each of the vanes is spaced from an adjacent vane by a gap measured from a first point on a first vane to a corresponding point on an adjacent vane, each vane also having a chord length at the first point measured from the vane leading edge to the vane trailing edge, the fan assembly having a ratio of chord length to vane gap of no less than about 0.2 and no greater than about 3.5.

2. The fan assembly as claimed inclaim 1, wherein the ratio of chord length to vane gap is no less than about 0.5 and is no greater than about 2.5.

3. The fan assembly as claimed inclaim 1, wherein the ratio of chord length to vane gap is no less than about 1.0 and is no greater than about 2.0.

4. The fan assembly as claimed inclaim 1, wherein the rearward swept angle is no less than about 10 degrees and is no greater than about 35 degrees.

5. The fan assembly as claimed inclaim 2, wherein the rearward swept angle is no less than about 10 degrees and is no greater than about 35 degrees.

6. The fan assembly as claimed inclaim 3, wherein the rearward swept angle is no less than about 10 degrees and is no greater than about 35 degrees.

7. The fan assembly as claimed inclaim 1, wherein the rearward swept angle is no less than about 10 degrees and is no greater than about 25 degrees.

8. The fan assembly as claimed inclaim 2, wherein the rearward swept angle is no less than about 10 degrees and is no greater than about 25 degrees.

9. The fan assembly as claimed inclaim 3, wherein the rearward swept angle is no less than about 10 degrees and is no greater than about 25 degrees.

10. The fan assembly as claimed inclaim 1, wherein:

each vane has an inlet angle defined between a straight line tangent to the vane at the leading edge of the vane and a plane orthogonal to the axis of rotation of the fan;

the straight line lies in a plane tangent to an imaginary cylinder centered at the axis of the fan; and

the inlet angle is no less than about 20 degrees and is no greater than about 70 degrees.

11. The fan assembly as claimed inclaim 10, wherein the inlet angle is no less than about 30 degrees and is no greater than about 60 degrees.

12. The fan assembly as claimed inclaim 10, wherein the inlet angle is no less than about 45 degrees and is no greater than about 55 degrees.

13. The fan assembly as claimed inclaim 1, wherein:

each vane has an outlet angle defined between a straight line tangent to the vane at the trailing edge of the vane and a line parallel to the axis of the fan;

the outlet angle is no less than about 30 degrees in a direction counter to rotation of the fan and is no greater than about 30 degrees in a rotational direction of the fan.

14. The fan assembly as claimed inclaim 13, wherein the outlet angle is no less than about 10 degrees in a direction counter to rotation of the fan and is no greater than about 20 degrees in a rotational direction of the fan.

15. The fan assembly as claimed inclaim 13, wherein the outlet angle is no less than about 5 degrees in a direction counter to rotation of the fan and is no greater than about 10 degrees in a rotational direction of the fan.

16. The fan assembly as claimed inclaim 1, wherein the fan is separated from the shroud by an axial gap between the leading edges of the vanes and the trailing edges of the fan blades, the gap being no less than about 0.15 inches and no greater than about 1.5 inches.

17. The fan assembly as claimed inclaim 16, wherein the gap is no less than about 0.20 inches and is no greater than about 1.0 inches.

18. The fan assembly as claimed inclaim 16, wherein the gap is no less than about 0.25 inches and is no greater than about 0.5 inches.

19. The fan assembly as claimed inclaim 1, wherein:

each fan blade has a blade root and a blade tip;

each fan blade has a twisted shape along a length of the fan blade from the blade root to the blade tip, the twisted shape defining a twist angle of the blade; and

the blade twist angle is no greater than about 45 degrees.

20. The fan assembly as claimed inclaim 19, wherein the blade twist angle is no less than about 5 degrees and is no greater than about 25 degrees.

21. The fan assembly as claimed inclaim 19, wherein the blade twist angle is no less than about 8 degrees and is no greater than about 18 degrees.

22. The fan assembly as claimed inclaim 1, wherein:

each blade has a pitch angle with respect to a plane orthogonal to the axis of the fan; and

the pitch angle is no less than about 10 degrees and is no greater than about 35 degrees.

23. The fan assembly as claimed inclaim 22, wherein the pitch angle is no less than about 12 degrees and is no greater than about 30 degrees.

24. The fan assembly as claimed inclaim 22, wherein the pitch angle is no less than about 15 degrees and is no greater than about 23 degrees.

25. The fan assembly as claimed inclaim 1, wherein each of the vanes has an airfoil shaped cross section.

26. The fan assembly as claimed inclaim 1, wherein each of the vanes has a cambered surface defining a curved shape extending from the leading edge of the vane to the trailing edge of the vane.

27. A fan assembly, comprising:

a motor;

a leading edge;

an inlet angle defined between a straight line tangent to the vane at the leading edge of the vane and a plane orthogonal to the axis of the fan, wherein the straight line lies in a plane tangent to an imaginary cylinder centered at the axis of the fan, the inlet angle being no less than about 20 degrees and is no greater than about 70 degrees;

28. The fan assembly as claimed inclaim 27, wherein the ratio of chord length to vane gap is no less than about 0.5 and is no greater than about 2.5.

29. The fan assembly as claimed inclaim 27, wherein the ratio of chord length to vane gap is no less than about 1.0 and is no greater than about 2.0.

30. The fan assembly as claimed inclaim 27, wherein the inlet angle is no less than about 30 degrees and is no greater than about 60 degrees.

31. The fan assembly as claimed inclaim 28, wherein the inlet angle is no less than about 30 degrees and is no greater than about 60 degrees.

32. The fan assembly as claimed inclaim 29, wherein the inlet angle is no less than about 30 degrees and is no greater than about 60 degrees.

33. The fan assembly as claimed inclaim 27, wherein the inlet angle is no less than about 45 degrees and is no greater than about 55 degrees.

34. The fan assembly as claimed inclaim 28, wherein the inlet angle is no less than about 45 degrees and is no greater than about 55 degrees.

35. The fan assembly as claimed inclaim 29, wherein the inlet angle is no less than about 45 degrees and is no greater than about 55 degrees.

36. The fan assembly as claimed inclaim 27, wherein:

37. The fan assembly as claimed inclaim 36, wherein the outlet angle is no less than about 10 degrees in a direction counter to rotation of the fan and is no greater than about 20 degrees in a rotational direction of the fan.

38. The fan assembly as claimed inclaim 36, wherein the outlet angle is no less than about 5 degrees in a direction counter to rotation of the fan and is no greater than about 10 degrees in a rotational direction of the fan.

39. The fan assembly as claimed inclaim 27, wherein the fan is separated from the shroud by an axial gap between the leading edges of the vanes and the trailing edges of the fan blades, the gap being no less than about 0.15 inches and no greater than about 1.5 inches.

40. The fan assembly as claimed inclaim 39, wherein the gap is no less than about 0.20 inches and is no greater than about 1.0 inches.

41. The fan assembly as claimed inclaim 39, wherein the gap is no less than about 0.25 inches and is no greater than about 0.5 inches.

42. The fan assembly as claimed inclaim 27, wherein:

each fan blade has a blade root and a blade tip;

the blade twist angle is no greater than about 45 degrees.

43. The fan assembly as claimed inclaim 42, wherein the blade twist angle is no less than about 5 degrees and is no greater than about 25 degrees.

44. The fan assembly as claimed inclaim 42, wherein the blade twist angle is no less than about 8 degrees and is no greater than about 18 degrees.

45. The fan assembly as claimed inclaim 27, wherein:

46. The fan assembly as claimed inclaim 45, wherein the pitch angle is no less than about 12 degrees and is no greater than about 30 degrees.

47. The fan assembly as claimed inclaim 45, wherein the pitch angle is no less than about 15 degrees and is no greater than about 23 degrees.

48. The fan assembly as claimed inclaim 27, wherein each of the vanes has an airfoil shaped cross section.

49. The fan assembly as claimed inclaim 27, wherein each of the vanes has a cambered surface defining a curved shape extending from the leading edge of the vane to the trailing edge of the vane.

50. A fan assembly, comprising:

a motor;

a length defined between a radially inner end of the vane and a radially

outer end of the vane;

a leading edge;

an outlet angle defined between a straight line tangent to the vane at the trailing edge of the vane and a line parallel to the axis of the fan, wherein the straight line lies in a plane tangent to an imaginary cylinder centered at the axis of the fan; the outlet angle being no less than about 30 degrees in a direction counter to rotation of the fan and is no greater than about 30 degrees in a rotational direction of the fan;

51. The fan assembly as claimed inclaim 50, wherein the ratio of chord length to vane gap is no less than about 0.5 and is no greater than about 2.5.

52. The fan assembly as claimed inclaim 50, wherein the ratio of chord length to vane gap is no less than about 1.0 and is no greater than about 2.0.

53. The fan assembly as claimed inclaim 50, wherein the outlet angle is no less than about 10 degrees in a direction counter to rotation of the fan and is no greater than about 20 degrees in a rotational direction of the fan.

54. The fan assembly as claimed inclaim 51, wherein the outlet angle is no less than about 10 degrees in a direction counter to rotation of the fan and is no greater than about 20 degrees in a rotational direction of the fan.

55. The fan assembly as claimed inclaim 52, wherein the outlet angle is no less than about 10 degrees in a direction counter to rotation of the fan and is no greater than about 20 degrees in a rotational direction of the fan.

56. The fan assembly as claimed inclaim 50, wherein the outlet angle is no less than about 5 degrees in a direction counter to rotation of the fan and is no greater than about 10 degrees in a rotational direction of the fan.

57. The fan assembly as claimed inclaim 51, wherein the outlet angle is no less than about 5 degrees in a direction counter to rotation of the fan and is no greater than about 10 degrees in a rotational direction of the fan.

58. The fan assembly as claimed inclaim 52, wherein the outlet angle is no less than about 5 degrees in a direction counter to rotation of the fan and is no greater than about 10 degrees in a rotational direction of the fan.

59. The fan assembly as claimed inclaim 50, wherein the fan is separated from the shroud by an axial gap between the leading edges of the vanes and the trailing edges of the fan blades, the gap being no less than about 0.15 inches and no greater than about 1.5 inches.

60. The fan assembly as claimed inclaim 59, wherein the gap is no less than about 0.20 inches and is no greater than about 1.0 inches.

61. The fan assembly as claimed inclaim 59, wherein the gap is no less than about 0.25 inches and is no greater than about 0.5 inches.

62. The fan assembly as claimed inclaim 50, wherein:

each fan blade has a blade root and a blade tip;

the blade twist angle is no greater than about 45 degrees.

63. The fan assembly as claimed inclaim 62, wherein the blade twist angle is no less than about 5 degrees and is no greater than about 25 degrees.

64. The fan assembly as claimed inclaim 62, wherein the blade twist angle is no less than about 8 degrees and is no greater than about 18 degrees.

65. The fan assembly as claimed inclaim 50, wherein:

66. The fan assembly as claimed inclaim 65, wherein the pitch angle is no less than about 12 degrees and is no greater than about 30 degrees.

67. The fan assembly as claimed inclaim 65, wherein the pitch angle is no less than about 15 degrees and is no greater than about 23 degrees.

68. The fan assembly as claimed inclaim 50, wherein each of the vanes has an airfoil shaped cross section.

69. The fan assembly as claimed inclaim 50, wherein each of the vanes has a cambered surface defining a curved shape extending from the leading edge of the vane to the trailing edge of the vane.

70. A fan assembly, comprising:

a motor;

a leading edge; and

a trailing edge downstream of the leading edge of the vane with respect to fluid flow through the fan assembly, wherein the shroud is separated from the fan by an axial gap between the leading edges of the vanes and the trailing edges of the fan blades, the gap being no less than about 0.15 inches and no greater than about 1.5 inches;

71. The fan assembly as claimed inclaim 70, wherein the ratio of chord length to vane gap is no less than about 0.5 and is no greater than about 2.5.

72. The fan assembly as claimed inclaim 70, wherein the ratio of chord length to vane gap is no less than about 1.0 and is no greater than about 2.0.

73. The fan assembly as claimed inclaim 70, wherein the gap is no less than about 0.20 inches and is no greater than about 1.0 inches.

74. The fan assembly as claimed inclaim 71, wherein the gap is no less than about 0.20 inches and is no greater than about 1.0 inches.

75. The fan assembly as claimed inclaim 72, wherein the gap is no less than about 0.20 inches and is no greater than about 1.0 inches.

76. The fan assembly as claimed inclaim 70, wherein the gap is no less than about 0.25 inches and is no greater than about 0.5 inches.

77. The fan assembly as claimed inclaim 71, wherein the gap is no less than about 0.25 inches and is no greater than about 0.5 inches.

78. The fan assembly as claimed inclaim 72, wherein the gap is no less than about 0.25 inches and is no greater than about 0.5 inches.

79. A fan assembly, comprising:

a motor;

a shroud including a plurality of vanes extending transversely with respect to fluid flow through the fan assembly and through which fluid flows through the fan assembly, the vanes being located downstream of the fan and oriented to extend away from a central area of the shroud, each vane having a leading edge and a trailing edge downstream of the leading edge with respect to fluid flow through the fan assembly, each of the vanes spaced from an adjacent vane by a gap measured from a first point on a first vane to a corresponding point on an adjacent vane, each vane also having a chord length at the first point measured from the vane leading edge to the vane trailing edge, the fan assembly having a ratio of chord length to vane gap of no less than about 0.2 and no greater than about 2.5.

80. The fan assembly as claimed inclaim 79, wherein the ratio of chord length to vane gap is no less than about 0.5 and is no greater than about 2.5.

81. The fan assembly as claimed inclaim 79, wherein the ratio of chord length to vane gap is no less than about 1.0 and is no greater than about 2.0.