US20170205090A1 - Air-conditioner module and use thereof - Google Patents

Abstract

The heat and mass exchange (HMX) module comprises a plurality of plates in a spaced-apart arrangement and provided with a plurality of air channels for air flow and a plurality of liquid channels for flow of liquid, wherein a liquid channel is embodied at a surface of a plate and is arranged adjacent to an air channel with a mutual exchange surface, which liquid channel is provided with an entry and an exit. The module further comprising a distance holder arranged between a first and a second adjacent plates. The entry of the liquid channel is defined as a plurality of entry regions spaced apart by means of closed regions, which entry regions define entry points for the liquid into and onto the layer of wicking material, in which closed regions the distance holder extends between the first and the second plate.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application is a 371 national stage application of PCT Patent Application No. PCT/NL2015/050680, entitled “Air-conditioner module and use thereof,” filed on Sep. 30, 2015, which claims priority to Dutch Patent Application No. 2013565 filed on Oct. 2, 2014, the entire contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
• The invention relates to a heat and mass (HMX) exchange module comprising a plurality of plates in a spaced-apart arrangement and provided with a plurality of air channels for air flow and a plurality of liquid channels for flow of liquid, such as liquid desiccant material, wherein a liquid channel is embodied at a surface of a plate and is arranged adjacent to an air channel with a mutual exchange surface, which liquid channel is provided with an entry and an exit and which air channel is provided with an inlet and an outlet.
• The invention further relates to an conditioner apparatus therewith and to the use thereof for conditioning of air and/or other gas streams.
BACKGROUND OF THE INVENTION
• Liquid desiccant-based air conditioners are considered a promising energy-efficient alternative for existing air-conditioning systems. The liquid desiccant allows the absorption of humidity. Moreover, the liquid desiccant may be easily transported, so that the cooling or drying of air may be carried out at different locations. The air-conditioner suitably comprises a heat and mass exchange (hereinafter also HMX) module for dehumidification and for regeneration. These HMX modules are typically used in combination with evaporators for cooling of air.
• For sake of clarity, the term ‘HMX-module’ is used within the context of the present invention to refer to any module for use in a conditioning system for air and/or another gas. Where reference is made to an air-conditioner module, this is to be understood as synonym. The conditioning system may be arranged to condition humidity and/or temperature of the air. The conditioning system is typically used for air, such as available in offices, stables, houses, theatres, museums, sport halls, swimming pools and other buildings. The conditioning system may alternatively be used for conditioning an industrial gas flow.
• A typical example of liquid desiccant is a concentrated salt solution of LiCl. Such a salt solution however have as disadvantages that LiCl may be hazardous for human health and that the concentrated LiCl solution is highly corrosive. It is therefore to be avoided that the LiCl is carried over into the air during the air-conditioning. The liquid desiccant is therefore often used in combination with a membrane, such as for instance known from WO2009/094032A1. That prior document discloses a module design wherein flow of cooling fluid, desiccant flow and air flow are integrated into a single multilevel module. As shown in FIG. 1 of WO2009/094032A1, the air flow (inlet airstream) runs in parallel to the liquid desiccant flow. This reduces the overall both heat and mass transfer efficiency relative to a counter current flow design.
• Another option is the use of a porous material, more particularly a wicking material. One such module is known from WO00/55546 (Drykor). The desiccant is pumped by a pump from a reservoir via a pipe to a series of nozzles. These nozzles shower a fine spray of the desiccant into the interior of the chamber, which is filled with a cellulose sponge material. The desiccant slowly percolates downward through the sponge material into a further reservoir. Moist air entering the chamber via an inlet contacts the desiccant droplets. Since the desiccant is hygroscopic, it absorbs water vapour from the moist air and drier air is expelled through outlet. The use of a chamber filled with a sponge has however the disadvantage that the air should be flowing through the pores of the sponge. This evidently requires a high air pressure, and it still may lead to carry-over due to the irregular flow pattern that the air has to go. Moreover, the liquid desiccant could directly enter the air flow. Therefore, WO00/55546 mentions the use of a dripper system for dripping liquid desiccant on the cellulose sponge, so as to continuously wet the sponge, as an alternative to the spray nozzles. However, WO2013/094206 states in paragraph
• that a high flow rate of the desiccant is required. This has the disadvantage of desiccant droplet creation and consequent carryover into the air stream.
• Again a further option is known from WO2013/094206. This patent application proposes the use of a plurality of plates, wherein the surface is made more hydrophilic. This may be achieved either by coating with a very hydrophilic material, by fabrication of a micro-structured surface in a moderately hydrophilic material or by constraining the desiccant behind a vapour-permeable membrane. The microstructure may be produced at a macroscale by flocking with polymer fibres, by the use of microchannels or by application of a porous textile to the surface. Alternatively a nano-scale hydrophilic structure may be produced by proprietary surface treatment. In a specific example, use is made of a flocked surface of 0.5 mm nylon fibres. The plates of WO2013/94206 are furthermore provided with channels for cooling liquid at the inside of the plates. A parallel flow manifold feeding an open-cell foam desiccant distributor or a micro-channel desiccant distributor is provided to ensure an even distribution across the width of the plate. These distributors may have integral spacers to define and maintain the air gap between the plates. The parallel flow manifold is effectively embodied as a frame-shaped network of tubes placed on the plate. The distributors in a direction extend substantially perpendicular to the plates, so that one distributor overlies a plurality of plates.
• However, such a distribution system still has a risk of carryover. Although the micro-channel distributor as such is not disclosed in WO2013/094206, it is likely a plate with apertures. As is shown inFIG. 2, the manifold tube corresponding in shape to the distributor will provide the liquid desiccant solution in a direction perpendicular to a plate. The distributor cannot cancel out this flow direction of the liquid desiccant, at least not completely. As a consequence, liquid desiccant ejected from the distributor will have, at least partially, a flow direction from the plate into the air gap, which will lead to carry-over to some extent, i.e. to droplets falling into the air gap rather than carried in the microstructure layer.
• As to the open-cell foam desiccant distributor, carry-over can also be expected, since part of the surface of the foam will be exposed to the air-channel. There is no reason why liquid desiccant would not concentrate there and form droplets that are carried over into the air channel.
• A further type of module is known from WO2012/170887A1. This module type is again based on hollow extruded plates, through which a refrigerant material may flow. The plates are provided with a wicking layer on the external surfaces of the plates. In one embodiment, the wicking layers are covered with membranes. In an alternative embodiment, no membranes are present. Distribution plates or molded spreader inserts are present between the plates, and are present to ensure that the liquid desiccant spreads across the entire width of the wicking layer from a supply orifice. The distribution plates thereto comprise a horizontally arranged channel and vertically extending grooves. It is deemed preferable to limit the height of the wicking layer so that the distribution plate presses directly against the extruded plate, and the liquid desiccant enters the wicking layer only after passing through the grooves.
• However, it has been found that this type of module is prone to leakage of liquid desiccant into an air channel rather than into the wicking layer acting as liquid channel. In the embodiment without membrane, it appears not merely preferred but rather necessary that the height of the wicking layer is limited. Otherwise, the wicking layer will already get in contact with the liquid desiccant in the horizontally arranged channel. It then will typically swell, leading thereto that the liquid desiccant will flow downwards not just through grooves, but behind the wall of the distribution plate. The resulting situation is one wherein the liquid desiccant flows in an uncontrolled manner and the assembly will loose its stability. However, also in the preferred embodiment, leakage cannot be prevented. In fact, the downward flow of liquid desiccant through the grooves brings it to a surface of the wicking layer. Being at the surface, there is a risk of flowing into the air channel, particularly at higher flow rates of liquid desiccant. In fact, the resistance to enter the wicking layer may be higher than the resistance to form droplets.
SUMMARY OF THE INVENTION
• It is therefore an object of the invention to provide an HMX module of the type mentioned in the opening paragraph, wherein the liquid may be distributed onto the surfaces of the plate accurately, and wherein particularly the risk of carry-over of liquid desiccant into the air-stream is substantially reduced.
• Further objects relate to the provision of an air-conditioning apparatus therewith and the use of the HMX module and/or apparatus for air conditioning.
• According to a first aspect of the invention, this object is achieved in a heat and mass exchange module comprising a plurality of plates in a spaced-apart arrangement and provided with a plurality of air channels for air flow and a plurality of liquid channels for flow of liquid, wherein a liquid channel is embodied as a layer of wicking material present at a surface of a plate and is arranged adjacent to an air channel with a mutual exchange surface, which liquid channel is provided with an entry and an exit, wherein a plate is embodied as a sheet with a first and a second layer of wicking material, each having a mutual exchange surface with an air channel. The module further comprises a plurality of distance holders each arranged between a first and a second adjacent plates, said distance holder being strip-shaped and provided with a plurality of contact surfaces on each side facing a plate. The entry of the liquid channel is defined as a plurality of entry regions spaced apart by means of closed regions, in which closed regions the contact surfaces of the distance holder are in contact with the plates, which entry regions are defined as apertures between the distance holder and the plate, allowing the liquid to flowinto and onto the layer of wicking material, in which closed regions the distance holder extends between the first and the second plate, and said wicking material is compressed between the distance holder and the sheet. At least one container of liquid is present on top of the plurality of liquid channels and overlying said plurality of apertures.
• According to further objects, this HMX module is integrated into an apparatus and/or used for air conditioning, such as for instance without limitation dehumidification.
• The inventors have observed in investigations leading to the present invention that the risk of carry-over by means of droplet formation upon injecting of desiccant liquid in the liquid channel is significant. Particularly, without any counter measures, the amount of liquid desiccant that is introduced into the liquid channel may be so high, that the layer may expand and/or get deformed. The stiffness of the layer of wicking material, particularly a textile material, then is reduced, with the effect of increasing the risk of carry-over into the neighbouring air channel.
• This problem is solved by integrating the distributor of liquid desiccant with the distance holder between the plates. In effect, a separate distributor such as a component with a plurality of micro-channels, or a nozzle may be left out completely. Instead, the liquid channel is subdivided over its width into entry regions and closed regions. The entry of the liquid channel is arranged such, that the liquid channel is substantially closed in the closed regions, such that the liquid cannot enter the liquid channel. The closure of the liquid channel therein occurs by means of compression of the wicking material, which is typically porous. This compression is particularly arranged in that a plurality of plates and distance holders is pressed together and suitably kept pressed together, for instance by means of a frame.
• By arranging the container for liquid, typically a reservoir for liquid desiccant, on top of the apertures of the module, the need for channels for the liquid between the plates is avoided. This allows a reduction of the thickness of the distance holders, as compared to the prior art with separate distribution plates. Such small distance is suitably to arrive at a sufficient density of exchange surface between air channel and liquid channel. Particularly, it is deemed preferable that the module contains more than 50 sheets, and thus at least 50 distance holders. Moreover, it has been found that the arrangement in which a top reservoir has a small pressure drop, appears improved over the prior art, certainly over commercially available prior art such as a system based on Celdek™ material. As a consequence, the flow rate in the liquid channel may be controlled effectively by means of setting the pressure in the reservoir and/or the pressure drop over the liquid channel.
• It is deemed an advantage of the structure of alternating entry regions and closed regions, that the wicking material may swell by absorption of liquid, such that the apertures are in use are at least partially filled by the wicking material that is swollen with liquid. This reduces the open area within an aperture. However, by limiting the width of an aperture, the effective swelling may be limited, so as to prevent that the layer of wicking material will loose its shape. The extent of swelling is clearly dependent on the exact type of wicking material. Preferably, the width of an entry region is between 50% and 200% of the width of a closed region. For instance, the width of an entry region is between 50% and 200% of the thickness of the distance holder. Such dimensions are deemed suitable to arrive at a proper distribution of the liquid, while at the same time having sufficient contact surfaces for maintaining the integrity of the assembly.
• One specific advantage of the formation of an assembly of plates and distance holders according to the invention, wherein the layer of wicking material is compressed, at least in the closed regions, is that any manufacturing tolerance in the thickness of the plates may be compensated by means of the compression. In this manner, the final thickness of the assembly may be tuned to a predefined thickness. Also in that view, it has been understood by the inventors that the present invention is not limited to the use of liquid desiccant material, but that is also suitable in the event that the liquid is another material, such as water or a diluted aqueous solution, as for instance in an evaporator.
• The apertures functioning as entry regions may be defined as apertures or cavities in the distance holder. The creation of cavities in the distance holder is deemed beneficial. Particularly beneficial is a configuration wherein contact surfaces and cavities on opposite sides of the distance holder are aligned. This generates a distance holder that has, along the extension of the distance holder, alternating first and second areas with different thickness and also another rigidity or spring constant. This is deemed particularly useful to smoothen out any minor non-planarity, and therewith to prevent leakage between the surfaces within the assembly. Such non-planarities may be the result of imperfections in manufacturing or assembly, but also slight changes in dimensions due to variations in temperature.
• Alternatively or additionally, cavities or slits may be created in the plates. In the latter case, the layer of liquid desiccant material suitably extends over the cavities or slits, but that is not essential. The creation of the cavities into the distance holder appears beneficial, since the distance holder may have a larger thickness than the plate and be therefore overall a more rigid material. Moreover, the distance holder may overall have smaller dimensions that are defined at higher resolution than the plate.
• Preferably, shape and size of the entry regions as well as the distance between adjacent entry regions are designed so as to achieve wetting over the entire area of the liquid channel under the foreseen operating conditions. For instance, the slots defined by the entry regions could widen in downward direction, so as to create some lateral flow. Alternatively, the slots could be defined so as to increase resistance against lateral flow with the air in the air channel, for instance in that such slot has an orientation that includes a sharp angle rather than a perpendicular angle to the air channel (‘partially against the wind’).
• The guided flow through the entry regions (particularly the non-compressed areas of the wicking material) moreover has the advantage that the flow rate may be specified. One implementation hereof is by setting the cross-sectional area of the entry regions, more particularly the apertures.
• In a further implementation, the closure of the liquid channel in the closed regions may be partial, i.e. that the flow of liquid, such as liquid desiccant material, and also the deformation of the layer of wicking material by means of the absorption of the liquid is reduced relative to that in the entry regions. The reduction could be a reduction to for instance at most 30%, such as at most 20% or at most 10% of the flow rate in the entry regions.
• In one embodiment the container overlying at least some of the apertures overlies all apertures, i.e. there is one container covering the module. In an alternative embodiment, there are more than one container overlying a single module. The container is suitably provided with an inlet. The container may also be provided with a further outlet. The container is in one embodiment designed as a storage container for the liquid. In an alternative embodiment, the container may be designed to be filled with liquid to a predefined level, and/or to a (variable) level controlled by the controller.
• In a specific implementation hereof, the HMX module comprises at least one spacer defined at a side of the module, and extending in a direction crossing the plurality of plates, typically perpendicular to the distance holder at the entry of the liquid channel. Such a spacer is more preferably strip-shaped, so as to cover an inlet of the air channels merely to a limited extent. It most suitably is provided with means for gripping side-edges of the plurality of plates. Therefore, it may only be assembled to the plates if the plates are present at the predefined mutual distance, notwithstanding the manufacturing tolerance. Good results have been obtained with a module comprising a distance holder at the top side between the plates and a couple of spacers at a side of the module. It turned out feasible to create a stable module have more than 50 plates and even more than 100 plates. Preferably herein, the plates—at least most of them—contain two layers of wicking material, i.e. one on the front and on the rear surface. Therewith, the overall number of liquid channels may be even twice as high as the number of plates. In this module, it turned out feasible to accurately hold the distance between the plates with the distance holders and spacers, at the top side and side faces of the module, all of which were effectively outside the liquid channel. This prevented creation of further locations of carry-over (i.e. since there were no distance holders inside the liquid channels).
• The distance holders in accordance with the invention are most suitably separate items extending along the width of the liquid channel, i.e. with a length corresponding to or larger than the width of the plate. However, it is not excluded that a plurality of distance holders are integrated, for instance by means of assembly, into a frame comprising slits into which the plates may be inserted at their top sides.
• In again a further embodiment, the distance holder is provided with a surface of a hydrophobic material. The advantage of a distance holder with such a surface is that the polar liquid desiccant comprising a salt solution (i.e. a ionic solution) is not attracted by but rather repulsed from the distance holder. As a consequence, the surface of the distance holder will normally not be wetted by the liquid desiccant, and undesired distribution of liquid desiccant is prevented. Such a hydrophobic material may be a coating of a specific material, for instance a polymer material such as a polyolefin, a halogenated material, but it may be alternatively a surface layer of a material that is made hydrophobic. Silica for instance, can be hydrophobic or hydrophilic depending on its surface. The material of the surface may be equal or different to the base material of the distance holder. Preferably, the distance holder is based on one or more polymer materials, and is for instance prepared by a moulding technique, even though alternative manufacturing techniques known in the field of polymer engineering are not excluded. It is deemed suitable that the distance material is based on the same polymer material as the plates are, for instance a polyolefin. This is deemed preferable in order to avoid as much as possible issues with respect to thermal cycling, i.e. differential thermal expansion leading to stress and strain with the risk of deformation and/or crack formation.
• In again a further embodiment, the distance holder has a bottom surface that is exposed to at least one air channel, which bottom surface has a concave shape between lower edges adjacent to the plates and an upper area between said edges. The distance holder of this embodiment is further designed so that any liquid desiccant does not form droplets on the bottom surface of the distance holder. An (inversed) V-shape is understood to be one of the possible implementations of a concave shape according to this further embodiment.
• In again a further embodiment, the distance holder is provided on at least one of its end faces with a clamping means, for holding a first and an adjacent second distance holder and an intermediate plate together. Such clamping means are deemed advantageous in the assembly of the holders and the plates. Furthermore, such means may further stabilize the assembly during use. The clamping means may be a monolithic portion of the distance holder. Alternatively, the clamping means may be connected to the distance holder, for instance in that a clamping means further comprises a pin or other protruding element for insertion into a corresponding hole in the distance holder, or vice versa, or another lock & key combination.
• Furthermore, it is deemed suitable that the distance holders and the plates are arranged such that their top surfaces are substantially aligned. This provides minimum risk for either carry over or uncontrollable swelling of the wicking material.
• The plates used in the module of the invention are sheets to which layers of wicking material are adhered or laminated. Thus, more particularly, the sheets are elements that are not hollow. The sheets typically comprise a carrier layer. Suitably, the carrier layer is of a thickness such that the sheet remains bendable or flexible. This flexibility is deemed advantageous for the generation of the assembly by pressing together the plates and distance holders. Preferably such sheets are corrugated, for definition of stiffness. Most suitably, the sheets are provided with an area at their top side that is substantially planar. This facilitates the assembly of the distance holders and the sheets. The term ‘sheet’ is used in the context of the invention as referring to a foil that is not completely rigid. Particularly, the sheet is based on a carrier material to which one or more layers of wicking material are applied. The sheet is most suitably provided with a shape, for instance by means of thermoforming or moulding, so as to provide appropriate stiffness and to increase the exchange surface between an air channel and an adjacent liquid channel.
• It is furthermore preferred that the wicking material is a textile material. This textile material is preferably a non-woven material, suitably comprising a web of spunlaced fibres. It is believed that such a material may be compressed accurately, which is beneficial in relation to the present invention. Good results have been obtained with rayon and materials containing rayon, for instance materials containing at least 50% viscose, and more preferably at least 65 wt % non-woven material or even at least 80 wt % non-woven material, such as viscose. The higher content of non-woven material, preferably spunlaced, is deemed beneficial so as to limit the swelling of the wicking material. This appears to facilitate a robust design of the distance holder, and to limit forces within the entry regions of the liquid channel on the distance holder. Such forces may reduce the life time of the distance holder and hence the HMX module.
• Additionally, the layer of wicking material may be filled up in the closed regions, such that it becomes effectively closed. Suitable fillers may be polymers, rigid and non-dissolvable inorganic materials such as silica or alumina. However, this requires patterning of the sheet with the wicking material, which is deemed disadvantageous.
• The HMX module of the invention is suitably used in an air-conditioner apparatus. This apparatus typically comprises a dehumidifier and a cooler, a regenerator, a cycle for transport of a fluid between said dehumidifier and said regenerator and pumping means for pumping the fluid. A single HMX module of the invention can herein be used either as such as a dehumidifier or as a regenerator, when its liquid channel is loaded with liquid desiccant during operation. When adding means for setting the temperature of the flows of liquid within such system, and/or with additional modules, it could also be made to work as a cooler or heater. It is not excluded that HMX modules of the invention are used for both the dehumidifier and the regenerator. The design of such HMX module is suitably elaborated in view of its function. Moreover, the HMX module of the invention could further be used as an evaporative cooler, for instance when its liquid channels are loaded with water or a diluted aqueous solution, for instance. It is added hereto, that it may be useful to provide an air-conditioner apparatus that is based on modules that all are of the same design. However, the HMX module of the invention could also be applied in an apparatus that is just for dehumidifying air.
• According to a further aspect of the invention, a method of air conditioning is provided, using an air conditioner module of the invention. This method comprises the steps of (i) providing an air flow into the plurality of air channels, and providing liquid desiccant material into the at least one container, resulting in a liquid flow into the liquid channels.
• According to a specific embodiment, the air flow is controlled to be a laminar flow. Controlling the air flow to be laminar has the advantage of minimizing or even eliminating carry-over. A disadvantage of laminar flow is however, that the heat and mass exchange with the adjacent liquid desiccant will be reduced. This disadvantage may however be avoided in that the module is designed to have a plurality of narrow air channels, so as to maximize the surface area at the edge between an air channel and a liquid channel. Preferably, a single air channel is present between two liquid channels.
• According to a further embodiment, a level of liquid desiccant in the at least one container is controlled, therewith defining a volumetric flow rate of the liquid flow.
BRIEF INTRODUCTION OF THE FIGURES
• These and other aspects of the air-conditioner module and the method of air conditioning are further elucidated with reference to following figures, which are not drawn to scale and are merely diagrammatical in nature. Equal reference numerals in different figures refer to identical or corresponding elements. Herein:
• FIG. 1 shows a diagrammatical view of a first embodiment of the HMX module;
• FIG. 2 shows a schematical view of a plate used in the HMX module;
• FIGS. 3a, 3band4 show diagrammatical views of implementations of such a plate;
• FIG. 5 show schematical side views of the module with a plurality of plates and distance holders according to one embodiment of the invention;
• FIG. 6ashows a schematical top view of an arrangement with plates and distance holders in one preferred implementation;
• FIG. 6bshows a detail ofFIG. 6a;
• FIG. 7a-cshows side views of a plate and manifold according to another implementation;
• FIG. 8 shows a schematical side view of a HMX module including a reservoir of liquid desiccant;
• FIG. 9-11 show graphs with test results of the HMX module of the invention.
DETAILED DISCUSSION OF ILLUSTRATED EMBODIMENTS
• FIG. 1 shows in a diagrammatical view a heat and mass exchange (HMX)module100 according to a first embodiment of the invention. TheHMX module100 comprises a plurality of plates, in this embodiment defined assheets10. The sheets are corrugated, as will be discussed with reference to following figures. Due to the corrugation and its orientation, the sheets, which are inherently flexible, are sufficiently stiffened so that they can be arranged at a relative short and uniform distance of each other without risking carry-over. Each of thesheets10 is in the preferred implementation provided with layers of wickingmaterial11 of both the front and the rear side of the sheet. As shown in thisFIG. 1, the layer of wickingmaterial11 may be subdivided into two lateral portions. However, this is not deemed particularly beneficial or preferred. TheHMX module100 is designed as a cross-flow module, such that the air and the liquid desiccant run in mutually perpendicular directions through themodule100. It will be clear that an entirely perpendicular design is deemed advantageous and most straightforward for manufacturing, since the sheets can be of rectangular shape. However, this is not deemed necessary. Alternative shapes, such as that of a parallelogram, are not excluded. Preferably, the module is configured such that the air channel extends laterally and that the liquid channel of the liquid desiccant extends vertically. In this manner, the liquid desiccant will flow within theHMX module100 under the impact of gravity.
• The HMX module as shown inFIG. 1 comprisestube connections18,19 for the provision and removal of liquid desiccant. Their location is not deemed critical. Though not shown explicitly, it is furthermore deemed beneficial that a reservoir of liquid desiccant is present so as to overlie thesheets10 of the module. The advantage thereof is that the liquid desiccant may be distributed into and onto thelayers11 of wicking material through apertures in a bottom of such reservoir, and typically spread over the entire surface thereof. Therewith, it is prevented that an initial flow of the liquid desiccant in a lateral direction needs to be converted into flow in a vertical direction.
• The HMX module as shown inFIG. 1 may be used both as a dehumidifier and as a regenerator module. In a dehumidifier module—also referred to as a drier module—a stream of air is dried, and the liquid desiccant takes up humidity. In a regenerator module, a flow of liquid desiccant is dried and the air in the adjacent air channel is humidified. There is no need that exactly the same design of a module is used for the dehumidifier as for the regenerator module. By means of temperature control, the dehumidifier module may further be arranged to operate as a cooler. The shown HMX module as shown inFIG. 1 comprises a plurality of sheets. The number of sheets can be chosen as desired in dependence of climate, air volume to be conditioned and space. As apparent fromFIG. 1 the liquid channel is suitably longer than the air channel, particularly in a drier module. With a well regenerated liquid desiccant, for instance an aqueous LiCl solution of sufficient concentration (i.e. typically close to the maximum loading concentration), drying turns out more effective in the first portion of the air channel.
• FIG. 2ashows in a schematical view asheet10 for use in the HMX module of the invention. Anair channel20 is defined between twosheets10 and is indicated for sake of reference. It is configured in a lateral direction. Theair channel20 is provided with aninlet21 and anoutlet22. Air in theair channel20 will first pass anaccommodation area23 then anactive area25 and finally anoutlet area24. Theactive area25 is configured to enable exchange with theliquid channel30 that is defined at the surface of the layer of wicking material (on the sheet10). It is observed for clarity that the layer of wicking material may extend beyond theactive area25. However, theactive area25 is further defined by means of the entry regions of the liquid desiccant, which are defined at theinlet31 of theliquid channel30. These entry regions are typically defined by means of the distance holder according to the invention, as will be further elucidated with reference toFIGS. 5-7. Theliquid channel30 is ended at theoutlet32. Thisoutlet32 is suitably embodied as a container for the liquid of several parallelliquid channels30. It can be seen that theliquid channel30 thus has a width (i.e. substantially as defined by the active area25), which is smaller than the length of the air channel20 (i.e. the distance between theinlet21 and theoutlet22 thereof). For sake of clarity, it is observed that the term ‘air channel’ refers in the context of the present application to a volume with a length and a width and a height, with dimensions that are typically for sheets of material. More specifically, the length and the width are much larger than the height of the air channel. In one embodiment, the length and width of the air channel are substantially identical to a width and length of a sheet. Similarly, the term ‘liquid channel’ particularly refers to a liquid layer at the surface of the wicking material. The dimensions are at most equal to the dimensions of the wicking material, but may be smaller, particularly as a result of the arrangement of the entry into the liquid channel.
• FIG. 2bshows schematically the generation of a HMX module from a plurality ofsheets10 and theair channels20 in between of thesheets10.FIG. 2cshows a representative corrugation when seen from the entry of theair channel20. The arrow defined the direction of theliquid channel30. The view ofFIG. 2cis in fact a cross-sectional view of the air channel.FIG. 2dshows a detail fromFIG. 2c. It is apparent from thisFIG. 2cthat in order to prevent carry-over, the liquid desiccant needs to have sufficient adhesion to the underlying surface. It preferably flows in a steady state. Most suitably, the film onto the surface of thelayer11 of wicking material (not shown in thisFIG. 2c) is sufficiently thin. The film thickness is thinned, in one preferred embodiment in accordance with the invention, by using a specific manifold, wherein the liquid desiccant first flows through a series of slots and is thereafter laterally distributed to cover the area of the liquid channel between the slots.
• As shown inFIG. 2d, the distance between thesheets10 varies somewhat due to the wave-shaped pattern of thesheets10. In fact, the distance a is larger than distance b. This variation in the distance is an important reason for arranging the wave along the length of the liquid channel rather than along the length of the air channel. If arranged along the length of the air channel, the variation in distance would result in a temporary narrowing of the air channel, resulting in an increase in flow rate (followed by a reduction in flow rate). Such variations in air flow rate would increase the risk of carry-over. By arranging the waves along the length of the liquid channel, the distance between the sheets (i.e. the height of the air channel) is substantially constant along its length.
• In one implementation according to the invention—not shown—the height of a ridge and a valley is higher in the middle part of the air channel than close to theoutlet area24. Herewith, it may be prevented that carry-over occurs at the end of the air channel due to a sudden change in direction of the air channel. In one further or additional implementation according to the invention, the ridges and valleys extend from theactive area25 into theoutlet area24. Therewith, it is achieved that the end of said ridges and valleys, corresponding to a change in orientation of the air channel is at least substantially outside the exchange surface between air and liquid desiccant material. In again one further implementation, the height of ridges and valleys may be lower in a bottom part of the air channel than in a top part. It is understood by the inventors, that the liquid desiccant typically will gain velocity in the course of flowing downwards. In a dehumidifier module, it additionally may warm up. Therefore, the lower part is more sensitive to carry over. This may be compensated by less steep ridges and valleys, to prevent any ejection of single droplets of liquid desiccant.
• FIG. 3ashows in a diagrammatical view thesheet10 more specifically. Herein, it is indicated that thesheet10 is provided withridges12 andvalleys13, in alternating arrangement. Thesheet10 suitably has a shape of a wave, wherein theridges12 extend into a first direction and thevalleys13 extend into the opposite direction. With theseridges12 and valleys13 a corrugated surface is created that is deemed positive for the necessary strength of thesheet10, without increasing carry-over too much. Moreover, the edges of thesheet10 are at least substantially planar. This facilitates assembly of thesheet10 into the module, particularly by means of a distance holder as will be explained with reference to further figures.
• In the shown embodiment, theridges12 andvalleys13 extend parallel to the width of theliquid channel30, such that theliquid channel30 in fact includes a curved trajectory. However, theair channel20 is substantially planar over the width of the air channel, i.e. in the area where the liquid channel and the air channel have an interface. This has the advantage of minimizing disturbance of air flow. As a consequence, carry over can be prevented, at least substantially, while the sheets are very thin. In this manner, a large packing density of sheets per unit volume is achieved, resulting in a large exchange area between the air channels and the liquid channels.
• Thesheet10 is suitably created in a multistep process. In a first process, layers of wicking material are added to a carrier. The carrier is suitably an engineering plastic, such as PET, polycarbonate, high-density polyethylene and polypropylene. Good results have been achieved with materials having a high temperature resistance, such as polypropylene or high-density polyethylene. Polypropylene is particularly preferred. The wicking material typically comprises a fibrous material, such as a textile material, for instance cotton, linen, viscose or nylon fibres. Alternative hydrophilic, fibrous materials, such as starch and particularly treated starches, are not excluded. Natural rather than synthetic fibres are deemed preferred as a basis for the wicking material. Viscose is deemed a particularly preferred choice. Rather than a single material, a blend of materials may be applied, for instance a blend of a viscose with a carrier material, for instance an engineering plastic, such as polyethylene terephthalate, polyethylene, polypropylene, polyvinylchloride, polyester. A blend with up to 50 wt % carrier material, for instance 25-40 wt % carrier material is deemed very suitable. Preferably, use is made of a non-woven material that appears to be beneficial for the one or more further steps of the process, and particularly the shaping step, for instance by means of thermoforming. The addition process may be achieved either by dipping (passing of a bath), coating, or laminating. The laminating process is preferred.
• The carrier may have been pretreated to improve adhesion, for instance by means of a surface treatment (such as a plasma treatment), or in the provision of an adhesion promoter or even a glue layer. In one advantageous embodiment, use is made of lamination under pressure, wherein an interlayer is formed between the carrier and the layer of wicking material. Good results have been obtained therewith. An advantage of this joining technique is that there is no glue needed, which could be sensitive to dissolution under the impact of the liquid desiccant that is typically very salty and corrosive. The glue may further have an impact on the porosity of the wicking material, and therewith on its wicking properties. In a further process step, the combined material is then thermoformed so as to create the corrugation of the surface, more particularly the ridges, valleys and any protrusions. Herein, the use of non-woven material is deemed beneficial, as it provides less resistance against the concomitant extension than any woven material.
• FIG. 3afurthermore shows the presence ofspacers26, which preferably have a stripwise extension and are assembled to a plurality ofsheets10. Thespacers26 are arranged within theaccommodation area23 and theoutlet area24, which are most preferably substantially or completely planar. WhereasFIG. 3ashows 5spacers26 in saidareas23,24, the actual number may vary. In the present configuration, a larger number ofspacers26, for instance 12-25 per meter perarea23,24, seems useful, so as to act as a stiffener. Thespacers26 in theaccommodation area23 are oriented downwards in the configuration shown inFIG. 3a. Thespacers26 in theoutlet area24 are oriented upwards in the configuration shown inFIG. 3a. Such an orientation is deemed beneficial to prevent any accumulation of liquid desiccant material. Notwithstanding that thespacers26 are arranged outside the liquid channel, it has turned out that liquid desiccant material may accumulate thereon, particularly in the region close to the outlet of theair channel20 and the exit of theliquid channel30. The oblique orientation makes that the liquid desiccant will flow downwards back onto one of thesheets10. In order to prevent droplet formation, the distance holder preferably is provided with a concave shape in the area between adjacent sheets, such as an inversed V-shape.FIG. 3aalso showsspacers35 at the bottom side of the sheet.
• One further advantage of the design shown inFIG. 3a—as opposed to a design wherein theridges23 andvalleys13 are oriented along the width of theair channel20, is that the bottom side of the sheet does not need to be fixed within a rigid holder, so as to provide sufficient stiffness. The absence of such a rigid holder allows the sheets to hang down, for instance in a bath of liquid desiccant, or in a sponge. The sheet may then expand and contract freely during temperature variations, i.e. between use and non-use, or between operating at different temperatures. As is well known, polymers have a large coefficient of thermal expansion (CTE). The expansion and contraction upon temperature variations may lead to warpage and other artefacts, particularly if a sheet with a large CTE is fixed to a sheet or component with a smaller CTE. Due to the free edge, the expansion will not cause problems. It is observed for clarity, that a free edge is not the only solution to the problem of differential thermal expansion. However, not all of these known solutions, such as the use of an elastomer interlayer with a very large CTE, is feasible in the context of air-conditioner modules with liquid desiccant. The liquid desiccant is known to be corrosive, but the lifetime of the air-conditioner module is still required to be high.
• The configuration ofFIG. 3bdiffers from that inFIG. 3ain the shape of thespacers26. Herein, the distance holders are arranged in extending parts27, which extend outside thesheet10. The advantage hereof is that such an arrangement further reduces the risk that adistance holder26 will be covered with liquid desiccant. It is understood that the liquid desiccant, when it would flow outside the intended area of theliquid channel30, would follow the edge of thesheet10. Because thespacer26 is present in extending part27, it will remain dry. It is observed for clarity that extending parts27 could be applied only in limited regions, wherein liquid flow can be expected.
• FIG. 4 shows a further configuration of thesheet10 comprising a pattern ofridges12 andvalleys13 as well as stiffeningprotrusions15. In this preferred configuration, the pattern ofridges12 andvalleys13 is repetitive, and is arranged so that the trajectory of the air in the air channel is straight, while the liquid channel is curved along its length. In addition, thesheet10 comprises stiffening protrusions. These are arranged outside theactive area25, in which the pattern ofridges12 andvalleys13 is arranged, and effectively within theaccommodation area23 and theoutlet area24. In the present configuration, a first and asecond stiffening protrusion15 are defined, both extending in this configuration along the width of the air channel (i.e. along the width of theactive area25 as shown inFIG. 2). While a longer stiffening protrusion is deemed beneficial, it is not excluded that this long protrusion is subdivided into two or more shorter protrusions. Moreover, more protrusions could be present, particularly in the accommodation area and in the outlet area. This is however neither deemed necessary nor deemed advantageous. Bothprotrusions15 have the same dimensions in this configuration. Again, this may be useful, so as to obtain a design that is most symmetrical, but it does not appear necessary. However, it appears useful that the slope of the stiffening protrusions, particularly at the inside, i.e. the side facing the liquid channel, is smooth, and preferably less steep than the slope of the pattern ofridges12 andvalleys13. In fact, the steepness is preferably designed such that turbulence is generated to a very low extent, if at all.
• FIG. 5 shows thedistance holder40, which is embodied as a plurality ofstrips45 that are provided with a plurality of clamps57. These clamps57 are present at side faces of thesheets10.Side walls61 are present at the outside, so that the assembly of sheets and strips may be fixed and contained, particularly by means of a pressing operation. O-rings62 may be present to avoid leakage of liquid desiccant along thewalls61. Areservoir50 is present directly on top of thestrips45, and is defined by thesame side walls61. Although not shown, it would be perfectly possible to insert a bottom of the reservoir in the form of a sheet with apertures.
• FIG. 6aandFIG. 6bshow a top view of the manifold40 as shown inFIG. 5. Herein thestrip45 is provided with a plurality of contact surfaces47 that are in contact with thesheet10, and particularly thelayer11 of wicking material present thereon. The contact surfaces47 are mutually separated by means ofcavities48. It will be apparent that the number of contact surfaces47 may be varied.
• The operation of this strip for the distribution of liquid desiccant is more specifically and still schematically shown inFIG. 6b. In fact, due to the pressing action onto the assembly ofstrips45 andsheets10 as shown inFIG. 5, thelayer11 of wicking material will be compressed opposite the contact surfaces47. However, thelayer11 will not be compressed at the location of acavity48. This compression can be arranged that the layer of wicking material is effectively closed opposite acontact surface47, thus forming aclosed region39. At the location of acavity48, thelayer11 of wicking material is not closed. This region thus constitutes anentry region38, where liquid desiccant can enter from the reservoir50 (as shown inFIG. 9) into thelayer11 of wicking material.
• In theFIGS. 6(a) and 6(b), the distribution of theentry regions38 is uniform over the length of thesheets10. It is preferable that noentry regions38 are present in an area not overlying theliquid channel30, more particularly neither the portion overlying theaccommodation area23 nor the portion overlying the outlet area24 (shown inFIG. 2a).
• FIG. 7a-cdiscloses again an alternative implementation of the distribution system in accordance with the invention. Herein thesheets10 comprise slits16.FIG. 7ashows a schematical side view of asheet10.FIG. 7bshows a schematical front view of thesheet10.FIG. 7cshows an assembly of a plurality ofsheets10 withstrips45. In accordance with the present implementation, thestrips45 extend along thesheets10 and suitably have a uniform width. Thesheets10 are provided withslits16. Theslits16 in this figure are closed. That seems beneficial for the stability of the sheet, but is not strictly necessary.Extensions14 are present between theslits16.
• As shown inFIG. 7(b), and corresponding to the situation shown inFIG. 6(b), where thestrip45 is in contact with the sheet, i.e. at anextension14, a contact surface is present. This results in closing off thelayer11 of wicking material, and aclosed region39. At the location of aslit16, no contact is present, resulting in anentry region38.
• FIG. 8 is similar to the view ofFIG. 7c. The figure additionally shows the presence of areservoir50 of liquid desiccant, present between the walls51 that also press thestrips45 and thesheets10 together. Although not shown, it will be apparent to the skilled person that further tools and means may be present to maintain this assembly together.
• FIG. 9-11 show test results obtained with the invention. Tests were carried out with a research version of the air-conditioner module in accordance with the invention, in accordance withFIG. 1 and with the sheet as shown inFIG. 4 and the distance holder ofFIG. 5. The test version contained 120 sheets, each having layers of wicking material, more particularly of viscose, laminated thereto. This resulted in 240 exchange surfaces between liquid channels and air channels. A comparison is made with a module made with Celdek™ material with 5 mm thickness, such as known in the prior art. In all experiments, unless otherwise stated, the liquid desiccant was a solution of LiCl, typically with 40 wt %. The temperature of the liquid desiccant upon entry of the module was 15° C. The temperature of the ingoing air was 30° C., with a relative humidity of 75%.
• FIG. 9 shows the relationship between the pressure drop and the air flow rate through the module. The pressure drop is the pressure drop over the module. The results of the prior art are shown as a line with bullets. The results of the invention are shown as a straight line. The pressure drop was generated by means of a pump defining flow of the liquid desiccant. This figure shows that according to the prior art, the pressure drop strongly increases when the air flow rate is increased. The function is quadratic or exponential. A higher flow rate than 2500 m³/hr could not be achieved. This behaviour clearly shows the effect of turbulence. A higher pressure drop will furthermore strongly increase the risk of carryover and reduce the lifetime of the module. When setting the air flow rate in the low range, up to 1000 m³/hr, the pressure drop is very low. However, such a low air flow rate implies that the air-conditioner module needs to have a very large size to work for a specific air volume. Moreover, the prior art material is defined for operation under some turbulence, such that the drying efficiency with the low flow rate is low.
• Contrarily, the dependence between the pressure drop and the air flow rate in the module according to the invention is linear. This implies that the flow regimen in the module is laminar flow. It makes that the air flow can be increased to commercially viable values without increasing the risk of carryover. Experiments were made with the module of the invention to detect the occurrence of carry-over. It was observed that carry-over occurred only at flow rates of approximately 4500 m³/h and higher. The striped area shown inFIG. 13 indicates the “forbidden” area of operation in the module of the invention, so as to prevent carry-over. This allows a very high air flow, and still at a pressure drop that is strongly reduced in comparison to the prior art. In fact, the pressure drop in the invention at 4000 m³/h is approximately the same as that in the prior art at 2000 m³/h.
• FIG. 10 shows the drying effect obtained in accordance with the invention. Herein, the reduction in humidity was obtained in dependence of the temperature of the incoming air flow. The y-axis herein indicates humidity as g H₂O per kg of dry air. The upper line shows the relative humidity of the incoming air flow, when the relative humidity (RH) is 80%. The lower line shows the relative humidity of the air flow leaving the air-conditioner module. It turns out that for any temperature of the incoming air, the humidity in the reduced with at least 50%. At a high air temperature of 27° C., the air contains three times humidity as much as at 10° C. The reduction in humidity achieved with the module of the invention increases then to 75-80% reduction (from 18 g/kg to 4 g/kg).
• FIG. 11 shows a comparison of the drying efficiency (also known as dehydration effectiveness) of the modules of the prior art and the invention. This result was obtained for a high air temperature of 27.5° C. and a humidity content of 12-13 g/kg. This corresponds to a lower relative humidity (RH) than the 80% line shown inFIG. 10. It is apparent from this Figure that the tested module of the invention gives a drying efficiency in the range of 70-80% (line A). The prior art merely achieves 40-50% (line B). This strong increase in drying efficiency is obtained at even lower ratios between the LiCl and the air mass flow, thus with less LiCl flow at a given air flow rate, or alternatively equal LiCl flow at a higher air flow rate. The drying efficiency is calculated as the ratio of the actual dehydration to the maximum possible dehydration of the air. The maximum possible is the difference between the water vapour content of humid air at the air inlet and the equilibrium water vapour content of air in contact with the liquid desiccant solution.

Claims (23)

1. An heat and mass exchange (HMX) module comprising a plurality of plates in a spaced-apart arrangement and provided with a plurality of air channels for air flow and a plurality of liquid channels for flow of liquid, wherein a liquid channel is embodied as a layer of wicking material present at a surface of a plate and is arranged adjacent to an air channel with a mutual exchange surface, which liquid channel is provided with an entry and an exit, wherein a plate is embodied as a sheet with a first and a second layer of wicking material, each having a mutual exchange surface with an air channel,

Wherein

the module further comprising a plurality of distance holders each arranged between a first and a second adjacent plates, said distance holder being strip-shaped and provided with a plurality of contact surfaces on each side facing a plate,

the entry of the liquid channel is defined as a plurality of entry regions spaced apart by means of closed regions, in which closed regions the contact surfaces of the distance holder are in contact with the plates, which entry regions are defined as apertures between the distance holder and the plate, allowing the liquid to flow into and onto the layer of wicking material, in which closed regions the distance holder extends between the first and the second plate, and said wicking material is compressed between the distance holder and the sheet, and

at least one container of liquid is present on top of the plurality of liquid channels and overlying said plurality of apertures.

2. The HMX module as claimed inclaim 1, wherein the apertures are defined in the distance holder.

3. The HMX module as claimed inclaim 2, wherein the contact surfaces on opposed side faces of the distance holder are aligned and neighbouring contact surfaces are spaced by cavities.

4. The HMX module as claimed inclaim 1, wherein the apertures are defined in the plate.

5. The HMX module as claimed inclaim 1, wherein the distance holders have a larger thickness than the plates and constitute a more rigid material than the sheets.

6. The HMX module as claimed inclaim 1, comprising more than 50 sheets and more preferably at least 100 sheets.

7. The HMX module as claimed inclaim 1, wherein the distance holder defines a side wall to an air channel.

8. The HMX module as claimed inclaim 1, wherein the entry regions have in cross-sectional view different surface area along the width of the liquid channel.

9. The HMX module as claimed inclaim 1, further comprising a controller for controlling a flow rate of liquid by means of setting a level of liquid in the at least one container.

10. The HMX module as claimed inclaim 1, wherein the distance holder has a surface of a hydrophobic material.

11. The HMX module as claimed inclaim 1, wherein the distance holder has a bottom surface that is exposed to at least one air channel, which bottom surface has a concave shape between lower edges adjacent to the plates and an upper area between said edges.

12. (canceled)

13. The HMX module as claimed inclaim 1, further comprising a means for pressing together the plurality of plates and distance holders.

14. The HMX module as claimed inclaim 1, wherein clamping means are present on at least one end face of the distance holder, for holding a first and an adjacent second distance holder and an intermediate plate together.

15. The HMX module as claimed inclaim 1, wherein the sheets are embodied as corrugated sheets.

16. The HMX module as claimed inclaim 15, wherein the corrugated sheets have a substantially planar area at their top side.

17. An conditioning apparatus for air and/or another gas stream, comprising:

at least one of a dehumidifier and a cooler,

a regenerator,

a cycle for transport of a fluid between said at least one of dehumidifier and cooler, and said regenerator,

pumping means for pumping the fluid,

wherein the heat and mass exchange module as claimed inclaim 1 is used for at least one of the dehumidifier and cooler and the regenerator.

18. (canceled)

19. A method of air conditioning, using an HMX module as claimed inclaim 1, comprising the steps of

Providing an air flow into the plurality of air channels, and

Providing liquid into the at least one container, resulting in a liquid flow into the liquid channels.

20. The method as claimed inclaim 19, wherein the liquid is a liquid desiccant material.

21. The method as claimed inclaim 19, wherein the air flow is controlled to have a laminar flow.

22. The method as claimed inclaim 19, wherein a level of liquid desiccant in the at least one container is controlled, therewith defining a volumetric flow rate of the liquid flow.

23. (canceled)

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