MXPA06004228A - Heat exchange laminate - Google Patents

Abstract

A heat exchange laminate comprises a formable carrier layer at least partially covered with a flexible liquid retaining layer having an open structure. By forming such a laminate of two layers, desired properties such as the spatial distribution of the liquid retaining layer, can be imparted to the heat exchange laminate prior to forming. The laminate may then be conveniently formed into any desired shape by known manufacturing procedures for incorporation into a heat exchanger. The laminate may be used to cool a first fluid by evaporation of a liquid into a second fluid operating at or near its saturation point.

Description

HEAT EXCHANGE LAMINATE DESCRIPTION OF THE INVENTION The present invention relates to a laminate for a heat exchanger and more particularly to a laminate comprising a liquid retention layer for use in evaporative type heat exchangers. The invention also relates to a heat exchanger formed of the laminate and to a method of producing such a heat exchanger. There are a number of situations in which the heat exchange in combination of the evaporation of a liquid may be desirable. One situation is in the humidification of dry air. When the air is heated, its ability to transport moisture increases and therefore its relative humidity decreases if additional moisture is not added. In cold periods, heating installations that provide hot air to a building may require some form of humidification to compensate for this relative humidity decrease. In general, it has been recognized that relative humidity of less than 50% is undesirable. One way to increase humidity is to provide water to a porous medium within an air treatment unit. The hot air that passes over the medium can collect the additional humidity and transport it inside the Ref. 172415 building. By doing so, the heat exchange of the porous medium and its support also takes place. The humidification devices can be provided independently or can be combined with heaters, heat recovery devices, heat pumps, air conditioners and also with dew point coolers as described below. Another situation where the exchange of heat in combination with evaporation of a liquid is desirable is the evaporative cooler. The principle of evaporative heat exchange has been used for many centuries in several traditional ways. In general, by providing a liquid to a surface of a heat exchange plate and passing a gas, for example air, through the surface, evaporation of the liquid from the surface can take place. Evaporation of the liquid to steam requires the addition of considerable heat - mainly the latent heat of evaporation. This heat can be supplied by the heat exchange plate and by doing this, it will serve to cool it. In the following, although reference will be made to evaporative coolers that work with water, air and water vapor, it will be understood that the principles are, in general, equally applicable to other means of heat exchange. A particular form of evaporative heat exchanger is known as a dewpoint cooler.

A dew point cooler attempts to lower the temperature of a product air stream as close to the dew point temperature as possible. For air at a given absolute humidity, the dew point is the temperature at which the air reaches a relative humidity of 100%, at this point it becomes saturated and can not absorb additional moisture. The heat is removed from the product air stream by the evaporation of a quantity of liquid into another working air stream. Such a process is theoretically extremely efficient and does not require a compressor, as is the case for conventional refrigeration cycles. Many attempts have been made to perform such cycles but practical considerations have caused greater difficulties in approaching the dew point over most temperature ranges. In the following, the term dew point cooler will be used to refer to devices which cool a fluid at or near its initial dew point by heat transfer to cause the evaporation of a liquid in a working fluid operating at or near from its saturation point. A known form of dew point cooler operates countercurrently and uses a portion of the product air stream as the working air stream. In simple terms, air flows on a first side of a heat exchange element and is cooled by heat transfer to the element. A portion of the air is diverted again onto the second side of the heat exchange element. The second side of the heat exchange element is provided with a water supply and the transfer of heat from the heat exchange element to the water causes it to evaporate in the working air stream. The evaporation of water in the working stream requires substantial heat input corresponding to the latent heat of water evaporation. A device of this type is known from the United States patent US4976113 A of Gershuni et al. Another known device of US Pat. No. 6581402 A to Maisotsenko et al. Describes an alternative arrangement of a dew point cooler in a countercurrent configuration. The contents of both descriptions are hereby incorporated by reference in their entirety. It is believed that the supply of liquid to the second wet side of such a cooler is critical to achieve adequate cooling near the dew point. Coolers known in the past have covered the wet side completely with a porous water absorbing layer. If the air left by the first side is at the dew point, when it returns through the second wet side, it may initially be unable to absorb additional moisture since it may already be saturated. First it must be heated by the thermal input to move it away from the saturation line. Only at this point can additional moisture be absorbed with a corresponding latent heat transfer. The presence of a thick porous layer on the wet side however inhibits direct heat transfer from the heat exchange element to the air. For this reason, known chillers rarely fall below the humid bulb temperature of ambient air. While not wishing to be bound by theory, the applicant believes that successful cooling to the dew point can only be achieved in this type of device by providing progressive and repeated alternating heat transfer followed by latent heat transfer. In this way, each time the air absorbs an amount of water it returns to the saturation line and must be heated again by direct heat transfer before additional water can be absorbed. It is also believed that to achieve effective cooling, the water activity of the material surface of the wet side must be high so that it can easily deliver its moisture. The activity of water is defined by the relationship of the tendency of the material to release the water to that of the water itself. Therefore, a surface with a water activity of 1 will easily deliver all of its water by evaporation in an air flow through the surface while a surface with a water activity of 0 will not release some water under the same circumstances. In the following, the water activity reference is also proposed to apply to similar activity of other liquids used in place of water. A smooth metal surface such as aluminum has high water activity and therefore will easily deliver water. Unfortunately, however, it is not good at water retention and can not provide an effective water buffer for evaporation. It should be noted at this point, that for dew point coolers, there is an advantage in retaining or damping water provided to the wet side during periodic irrigations. If the wet side of a dew point cooler is irrigated, the presence of excess water in the working air stream will cause the temperature to rise from the dew point to the wet bulb temperature. This is because the excess water causes adiabatic cooling of the working air stream by evaporation of water droplets in the air stream itself rather than by the evaporation of the heat exchange wall. Once the irrigated water has been absorbed by the surface and some excess has been drained, the temperature can return back to the dew point. The water absorbed by the surface should be sufficient for the dew point cooler to continue operating for a period of time until the next irrigation. The ideal liquid retention layer should therefore be able to retain or dampen a large amount of liquid but should also deliver it easily on evaporation. A device is known from the German patent NL1018735, the content of which is hereby incorporated by reference in its entirety, in which a layer of Portland cement is used to coat the fins of a heat exchanger. Although it has been found that such a layer has excellent characteristics of water activity and water damping as a result of its open structure, it nonetheless exhibits certain disadvantages: it is relatively heavy; it is susceptible to exfoliation and spraying especially if the carrier layer in which it is formed is subjected to shock or bending; and it is inconvenient to apply it in a clean manufacturing environment. In particular, the cement coating must be applied to the formed product, since once coated, the material forming the heat exchanger can not be formed any longer. The application of a layer of a desired thickness distribution to a complex shape is difficult and it has been found that the cement coatings of the prior art show undesirable thickness variation. According to the present invention, there is provided an improved heat exchange laminate comprising a formable carrier layer at least partially covered with a flexible liquid holding layer having an open structure so that in use, an exchange medium of The heat can make contact directly with the carrier layer through the open structure of the liquid retention layer. By forming such a two-layer laminate, the desired properties such as the spatial distribution of the liquid retention layer can be imparted to the heat exchange laminate prior to forming. The laminate can then be conveniently formed into any desired shape by known manufacturing processes. By providing the liquid retaining layer with an open structure, the ability of the heat exchanger to transfer both heat and latent heat to a fluid medium flowing on it is improved. The open structure may comprise spaces between the fibers of a fibrous material that forms the liquid retention layer. Such a fibrous material may be a woven or non-woven layer having an open structure. In particular, knitting or other knotting techniques have been found to be extremely effective in producing an open structure having sufficient height to damp a considerable amount of liquid. The fibrous material can be attached to the carrier by adhesives or other similar methods. Preferably, the adhesive and the fibrous material should be such that the delamination does not take place in the formation of the laminate in a desired form. In the case of corrugation of the laminate, for example it may be desirable to align the wave of a woven fibrous material with the proposed corrugation. Additionally, where adhesive is used, the adhesive can be chosen to improve the properties of the carrier layer or liquid retention layer. Accordingly, the adhesive can be chosen to have water-retaining properties or heat-conducting properties, or both and therefore can be considered to form a part of any of these layers. The adhesive can be provided on both sides of the carrier layer prior to or during the lamination process. The adhesive on a first side of the carrier layer can serve to join the liquid retention layer while the adhesive on a second side can serve to join the formed laminate to an additional heat exchange element such as a membrane or to itself to form a tube. Preferably at least the adhesive on the second side of the carrier layer is a heat activated adhesive. According to a particularly advantageous embodiment of the invention a suitable fibrous material can comprise a mixture of polyester and viscous fibers.

Alternatively, polyester fibers coated with polyamide can be used. For use with water in a dew point cooler, it has been found that these fibers have both excellent water retention and high water activity and can retain sufficient water damping to allow intermittent water supply. Preferably the fibers should have diameters between 10 microns and 40 microns, more preferably about 30 microns. In an alternative embodiment of the invention, the heat exchange laminate may additionally or alternatively comprise covered and uncovered areas of the carrier layer, possibly in the form of a repeating configuration of bands or ridges of liquid retention material followed by bands of carrier layer not covered. The covered areas can be covered by the fibrous materials mentioned above or they can be covered by alternative liquid retention materials. Ideally, for use with water, such materials should have high water activity so that water is easily released where necessary. Preferably, the water should be retained mainly by surface tension effects. Alternatively, materials exhibiting weak hygroscopic and hydrophilic effects can be used, for example in the form of coatings such as polyurethane. Such coatings can be placed on the carrier layer in several different ways including painting, spraying, printing, transferring and the like. Of course, for use with evaporative media other than water or for use with gases other than air, other materials may be selected. In a preferred embodiment of the invention, the carrier layer comprises mild annealed aluminum. The aluminum may be in the form of a sheet having a thickness of between 30 and 150 microns. More preferably, the sheet has a thickness of between 50 and 100 microns, ideally about 70 microns. One of the main advantages of such aluminum is that it is relatively inexpensive and very easy to form. It is also extremely light yet structurally very strong. Copper can also be used but it is somewhat heavier. Other metals can also be considered depending on the price and weight considerations and also in the area of proposed use. The use of a good heat conductor such as a metal, for example aluminum, is extremely important where the laminate is required to conduct heat in the plane of the laminate. This may be the case when the laminate is formed into fins for mounting on a first side of a membrane separating a first fluid stream from a second fluid stream. In such a case the fins serve to effectively increase the surface area of the first side of the heat exchanger. Additional fins may also be provided on the second side of the membrane. Additional fins, if desirable, can also be formed from a laminate according to the invention. If aluminum is used as the carrier layer, the use of bonding with adhesive may require a primer. The primers may also be required for other materials that are difficult to adhere to. If the heat conduction in the plane of the laminate is not proposed or will be avoided, the carrier layer can be formed of a poor thermal conductor. This may be the case where the laminate is formed as a membrane that separates a first fluid stream from a second fluid stream and is only intended to transfer heat through itself from the first stream to the second stream. In this case, the carrier can be formed of a formable plastic material and the formation can take place by thermoforming, thermosetting, curing or any other method of producing a permanent or semi-permanent deformation. Advantageou for all the laminates mentioned above, the liquid retention layer should be relatively thin to ensure good heat transfer to the carrier layer. Ideally, it is believed that the average thickness of the liquid retention layer should be less than 50 microns. Preferably, less than 20 microns and even more preferably, less than 10 microns. With reference to the thickness of the liquid retention layer, reference is made to the average thickness, taking into account the distribution of covered and uncovered areas or otherwise the open structure of the layer. Accordingly, a liquid retention layer with a cover ratio of 50% space and a thickness of 40 microns could be considered to have an average thickness of 20 microns. If the liquid retention material additionally has an open fibrous structure, then the average thickness of the layer could be proportionally less than 20 microns. According to a still further aspect of the present invention there is further provided a heat exchange element formed from such a heat exchange laminate. Such a heat exchange laminate can be corrugated to form a series of elongated fins. The fins can be attached to a heat exchange membrane as elements that increase the surface area or can themselves be used to form the membrane or channel that defines the flow of fluid through a heat exchanger such as a heat exchanger. dew point. If the fins are attached to a heat exchange membrane as elements that increase the surface area, they may additionally be provided with blinds. It has been found that the use of such blinds is extremely advantageous in the case of a carrier provided with a liquid retention layer only on a first surface. In use, the blinds can serve to guide the flow of fluid from the first surface to the second surface and vice versa. Since the second surface is not covered by the liquid retention layer, the direct heat transfer from the carrier layer to the flow is improved. In such a case where the fluid flows alternately on both sides of the heat exchange laminate, the distribution of the liquid retention layer on both surfaces of the carrier layer can be part of the determination of the open structure ratio and the average thickness Effective water retention layer. According to a particular advantage of the present laminate, the heat exchange element may comprise a heat exchange laminate having a liquid retaining layer of open structure on both surfaces of the carrier layer. Such a heat exchange element is extremely versatile for use in evaporative type heat exchangers and dew point coolers. Due to the open structure, both sides of the laminate can function either as a wet side or as a dry side, depending on the direction of flow and the water supply. This allows the use of a dew point cooler as a heat recovery element during, for example cold periods and also allows the humidification of the incoming air stream. In this context, a particular advantage of the laminate according to the invention lies in the ability of the water retaining layer to retain and transport the water formed by the condensation on the cooling side of such a heat recovery element. In the past, such water has tended to form as droplets which may cause obstruction or restriction of the heat exchange elements. The presence of a liquid retention layer according to the present invention ensures that a thin film of water is retained, thus optimizing the heat transfer, while the excess water is drained. The recovered water can then be supplied to the hot side for humidification purposes. According to a still further aspect of the present invention there is provided a method of manufacturing a heat exchange element comprising providing a heat exchange laminate comprising a formable carrier layer at least partially covered with a liquid retention layer. flexible and form the laminate in a heat exchange element. By first providing the laminate and then forming it into the desired shape it is possible to achieve the desired configuration of the liquid retention layer. Once the heat exchanger has been formed in a complex way, it is otherwise difficult to join the liquid retention layer in an effective and controllable manner. Preferably the laminate is formed into a plurality of elongated fins. If the carrier layer is formed of a metal, for example aluminum, such fins can easily be formed by roll forming machines. The training process can also include the stage of forming blinds in or through the fins. These can help to further improve the heat transfer by separating the various boundary layers and can also serve to direct the flow from one side of the plate to the other. Other flow separation means can also be formed including dimples, projections, slots etc. In order to be able to effectively form such fins, shutters and other separation means, it is important that the carrier layer and liquid retention layer be well joined together to prevent unwanted delamination or other alteration to the integrity of the laminate. If the blinds are formed through the laminate, the formation may also include cutting the carrier layer or the liquid retention layer or both. In an advantageous embodiment of the method the laminate can be attached to a first surface of a membrane for heat transfer thereto. If the laminate is corrugated into fins, the base of each fin can be attached to the membrane preferably by adhesive. The heat exchangers of the prior art have generally been formed by welding and brass welding techniques. In accordance with an important development of the present invention, the attachment of the fins to the membrane by adhesive can allow a quick, cheap and light assembly. In particular, the adhesives activated with heat and pressure are favored which can be provided as an integral part of the laminate or membrane prior to forming and joining. According to a still further advantageous embodiment of the invention, the method additionally comprises providing additional fins and joining them to a second surface of the membrane for heat transfer thereto. A tubular structure can then be formed with the elongated fins on an outer surface of the tubular structure and the additional fins on an inner surface of the tubular structure or vice versa. The tubular structure can be formed by placing two similar membranes together and sealing them along the parallel edges. Alternatively, a single membrane can be folded or rolled into a tubular structure and sealed to itself. Preferably, the fins are generally aligned with the axis of the tubular structure. The embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: Figure 1 is a perspective view of a section of heat exchange laminate according to an aspect of the present invention; Figure 2 is a detailed cross section through the heat exchange laminate of Figure 1 illustrating water retention; Figure 3 is a perspective view of an alternative heat exchange laminate according to another aspect of the present invention; Figure 4 is a perspective view of a heat exchange element according to the present invention; Figure 5 is a perspective view of a construction using the heat exchange element according to Figure 4; and Figure 6 is a perspective view of a tubular structure comprising a number of heat exchange elements according to Figure 4. According to Figure 1, a section of a heat exchange laminate 1 is shown which illustrates the individual layers. The laminate 1 comprises a carrier layer 2 covered on its first surface by a liquid retention layer 4. A first adhesive 6 is provided between the carrier layer and the liquid retention layer. A second adhesive 8 is also provided on the second surface of the carrier layer 2. In this embodiment, the presence of the second adhesive 8 is optional and its function will be described in further detail below. The carrier layer 2 is preferably formed of mild annealed aluminum having a thickness of about 70 microns. It has been found that this material is extremely advantageous since it is light, easily formable and has good conductivity. The aluminum is provided on both surfaces with a primer (not shown) to ensure proper bonding with the adhesives 6, 8. The primer is preferably a PVC based primer and can be colored to provide a desirable appearance to the laminate 1. Additional coatings, for example to provide protection against corrosion may also be included. Although aluminum is represented in this embodiment, other metals having similar properties can also be used including copper, tin, zinc and other alloys and combinations. Alternatively, composite materials and plastics including aramid and carbon fibers can be used. The selection of the above materials will be evident to the expert man and will be determined by the particular conditions under which the heat exchanger intends to operate. The liquid retention layer 4 is formed of a fibrous nonwoven material. Although reference is made to a liquid retention surface, it is clearly understood that the surface in fact is a liquid retention and retention surface. As can be seen from figure 1, the layer has a very open structure so that the carrier layer 2 can be clearly seen through the space between the fibers 10. An exemplary material for forming the water retaining layer is a mixture of the same. / 50 polyester / viscose 20 g / m2, available from Lantor BV in the Netherlands. Another exemplary material is a polyester fiber coated with 30 g / m2 polyamide available under the name Colback ™ from Colbond N.V. in the Netherlands. Other materials having similar properties including synthetic and natural fibers such as wool can also be used. Where necessary, the liquid retention layer can be coated or otherwise treated to provide antibacterial or other anti-fouling properties. In Figures 1 and 2, the first adhesive 6 is provided as a thin layer over the entire area of the laminate 1. For use with aluminum and Lantor fibers as mentioned above, a layer of 2 microns of a two-part polyurethane adhesive components has been found to provide excellent results. When presented as such a thin layer, its effect on heat transfer to the carrier layer is negligible. However, it is also possible to provide the first adhesive 6 only in the area of the individual fibers 10. In this case it can also be considered to be part of the open structure, whereby both the liquid and the heat exchange medium can come into direct contact with the carrier layer 2. This can be achieved by coating the fibers 10 of the liquid retention layer 4 with the second adhesive 6 prior to the lamination with the carrier layer 2. Figure 2 shows in greater detail how the liquid retention layer 4 is effective to dampen an amount of liquid for subsequent evaporation. Figure 2 shows the carrier layer 2 provided with the second layer of adhesive 8 on its bottom surface. Two fibers 10 forming part of the liquid retention layer 4 are represented on their upper surface adhered by the first layer of adhesive 6. Also shown in Figure 2 is a drop of liquid 12. The liquid drop 12 is retained effectively by the fibers 10 and prevented from squeezing out of the surface even if the laminate 1 is held in a vertical position. Several mechanisms can be used to improve the tendency of the fibers to retain liquid. For water, retention should preferably be based primarily on surface tension effects, since these are accompanied by relatively high water activity. From figure 2, the extension of the open structure can also be seen. The fibers 10 are spaced apart by a distance d, which in this case corresponds substantially to the extension of the drop of liquid 12 retained by a fiber 10. The extension of the drop of liquid 12 in practice will depend on several factors including: the shape and dimensions of the individual fibers 10; the nature of the surfaces of the fibers 10, the adhesive 6 and the carrier layer 2; the liquid 12 used; and the nature and condition of the gas flowing through the heat exchanger. The choice of the distance d will also depend on the desired properties of the laminate 1. If the water activity is of primary importance, the spacing d can be chosen to be greater than the extension of the drop 12. If the increase in the capacity of Damping is of primary importance, the spacing d can be chosen to be substantially smaller than the extent of the drop. In practice, for use with water in an aluminum carrier coated with two-component polyurethane adhesive, it has been found that an average spacing d of about 100 microns is desirable. The liquid retention layer can therefore be adapted according to the expected conditions, for example by providing greater damping capacity for dryer climates. Figure 3 shows an alternative version of the laminate 1 in a vertical position. Similar elements will be designated with the same reference numbers as before. The laminate 1 comprises a carrier layer 2, provided on a first surface with isolated regions of adhesive 6. The adhesive 8 is similarly provided on the second surface of the carrier layer in the form of isolated regions. In this embodiment, the adhesives 6 and 8 by themselves constitute water retention layers. Similar to the fiber spacing in the case of Figure 2, the isolated regions of adhesive are spaced apart apart. In this case, however, it can be seen that the distance d is substantially smaller than the size of a drop of liquid 12 leading to the lower damping capacity but greater water activity. Several different methods of forming the adhesive liquid retention layers are possible including spraying, transfer and printing. A preferred method uses an inkjet printing technique. Clearly, the isolated regions can be provided in any desired form and can be arranged in any desired configuration. While reference has been made to isolated regions, the linked regions that provide the desired open structure can also be used. In addition, although the adhesive has been mentioned, other structures or protrusions on the surface of the carrier layer can provide the same water retention function. Similar effects can be achieved by surface treatment of the carrier layer, for example by etching to the acid or the like to produce liquid retention elements in a top layer of the surface. Surprisingly, it has been found that the height of a protrusion such as the adhesive 6, 8 of Figure 3, or the fibers 10 of Figures 1 and 2 is significant in determining the amount of water retained. By using knitting techniques to form the material of the liquid retention layer 4, the increased damping capacity can be achieved if the knitting method is optimized to increase the height or thickness of the layer without reducing its open structure . Figure 4 shows a section of heat exchange laminate 1 according to Figure 1, formed in a heat exchange element 14. The heat exchange element 14 comprises a series of fins 16 having the retention layer of liquid 4 in a first upper surface of this. The fins 16 are each provided with blinds 18 in the form of elongated slots penetrating through the laminate 1 (only the blinds on the first fin are shown). The blinds 18 are arranged in groups. A first group 20 serves to direct the flow on the surface, while a second group 22 directs the flow out of the surface. Accordingly, some of the air flowing along the heat exchange element 14 in the direction of the arrow A will be directed through the laminate to the second bottom surface. The air that follows the direction of arrow B will be directed outward by the second group of blinds. Thus, the air alternately flows on the first surface, where it can receive moisture by the evaporation of the liquid retention layer, followed by the second surface where it can receive the direct thermal energy to raise its temperature. In addition to its function in the direction of flow between the surfaces of the heat exchange element 14, the blinds 18 also serve to separate the boundary layers that can develop when the air flows along the surfaces. Other separation elements can be provided in addition to or in place of the blinds 18. It is noted that in a heat exchange laminate 1 according to a modality described in figure 2, the water retention elements can additionally be designed to separate the limit layer. Furthermore, while the fins 16 of Figure 4 are straight, curvilinear or zig-zag fins can also be produced. It is believed that such fin shapes are advantageous in separating the boundary layers that develop in the flow along the fins, since each time the fin changes direction, the turbulent flow is restored. Several shapes of cross section are also possible for the fins, including corrugations of square, trapezoidal, rectangular, bell and sinusoidal shapes. The precise shape will depend on several factors, one of which may be the ability of the liquid retention layer 4 to resist bending. In addition to the blinds 18, the heat exchange element 14 is provided with conducting bridges 24. These bridges 24 are in the form of cuts through the laminate 1 over substantially the full height of the fin 16. They serve to prevent transport undesired heat along the heat exchange element 14 in the direction of air flow. The heat exchange element 14 is preferably formed using standard corrugation techniques. A roll of appropriate width of the prepared laminate 1 can be fed through corrugated rolls which can form the fins 16, blinds 18 and heat bridges 24 in a single passage. The resulting product can then be cut into suitably sized heat exchange elements 14 for further processing. Fig. 5 shows a possible construction 25 using the heat exchange element 14 of Fig. 4. According to Fig. 5 the heat exchange element 14 is attached to a first surface of a membrane 26. The membrane 16 is provided in its second surface with a second heat exchange element 28, which in the present embodiment is provided with fins 30 formed similarly to the heat exchange element 14 and which can also be provided with blinds and conduction bridges. The second heat exchange element 28 differs from the first heat exchange element 14 in that it does not comprise a liquid retention layer. The membrane 26 is generally impermeable to air or other fluid proposed for use in the heat exchanger and serves to define a first fluid region X and a second fluid region Y. For constructive reasons, a preferred material for the membrane is aluminum soft annealing of approximately 70 microns of measurement. As described above, the heat exchange laminate 1 forming the heat exchange element 14 can have a second adhesive 8 on its second surface. This second adhesive 8 is preferably a heat sealing adhesive such as PVC / polyacrylate based adhesive. The membrane 26 is also provided with a compatible heat sealing adhesive or the like on its surface facing the heat exchange element 14 whereby both the membrane 26 and the element 14 can be easily joined together under appropriate heat and pressure. The facing surfaces of the second heat exchange element 28 and the membrane 26 are also provided with similar heat sealing adhesive and can be joined together in the same manner. As you can see from figure 5, the heat exchange elements 14 and 26 are joined in such a way that only the channels of the fins 16, 30 adhere to the membrane 26. In addition, the fins 16 and 30 are directly aligned with each other through the membrane 26. In use, the fluid region X can serve as the wet side of an evaporative heat exchanger or humidification device, while the Y region serves as the dry side. The fins 16 comprising the laminate 1 can absorb an amount of water in the liquid retention layer 4. The unsaturated air flowing through the surface can absorb water by the evaporation of the laminate 1. By doing so, the laminate 1 loses a quantity of heat corresponding to the latent heat of the evaporation of the water loss. To maintain balance, heat must be provided to the laminate 1. For a carrier layer 2 of aluminum, this takes place by conduction in the plane of the laminate from the membrane 26. This heat must in turn be supplied by the cooling of dry fluid in the region Y and by conduction of this heat through the fins 30 of the second heat exchange element 28 to the membrane 26. The alignment of the fins 11, 30 better the transfer of heat from one element to the other through the membrane 26. In the illustrated embodiment only a single side of the fins 16 is provided with a liquid retention layer. However, it is also possible to provide a liquid retention layer on other surfaces as well. The membrane 26, for example, can also be formed from the heat exchange laminate 1, which has the liquid retaining layer on its first surface facing the heat exchange element 14. It is also possible to use the heat exchange laminate 1 to form the second heat exchange element 28 and provide the liquid retention layers on both sides thereof. As an advantageous consequence of the open structure according to one aspect of the present invention, the liquid retention side of the laminate can work either as a wet side or as a dry side of a heat exchanger. For laminates provided with a liquid retention layer on both surfaces, additional measures and layers of adhesive may be required to ensure attachment to another surface. In the illustrated embodiment, the fins 16 and 30 are arranged to be parallel to one another so that the heat intercalator can operate in countercurrent. For use as a dewpoint cooler, the membrane may be provided with channels that allow some or all of the fluid in the Y region to pass through the membrane to the X region. Such channels may be in the form of holes through the membrane. Other alternative arrangements are also possible with the two sets of fins angulated with respect to each other for countercurrent operation. For countercurrent operation as a dew point cooler, it may also be possible to provide holes through the membrane between one or more of the fins 28 to serve as feeders for some or all of the channels between the fins 14 in the X region. The construction 25 according to Figure 5 can be integrated into a heat exchanger such as a dewpoint cooler in many different forms. A number of similar constructions 25 can be arranged parallel to one another to form a series of alternate fluid regions X and Y. Clearly, if a number of such constructions 25 are combined, more than two regions can each be defined by being attached to each other. a different fluid. In an advantageous alternative, the construction 25 can be formed into a tubular structure by rolling or bending the membrane and sealing it with heat to itself, whereby the Y region is located within the tube and the X region is located externally. Figure 6 shows a possible tubular structure 32 which has been found particularly advantageous for the construction of elements of dew point coolers and heat recovery elements. The tubular structure 32 comprises a pair of constructions 25 comprising membranes 26 that have been joined together at the upper and lower longitudinal edges 34, 36. Several methods for joining the edges 34, 36 can be used, but a preferred method for aluminum membranes 26 as described above is by heat sealing. The constructions 25 are effectively connected in back-to-back relation with the second heat exchange elements 28 inside and the heat exchange elements 14 with liquid retaining layer 4 on the outside. An inversion of this arrangement is also possible but could require water supply to the interior of the tubular structure 32 to wet the liquid retention layer 4. As can be seen from Figure 6, the exterior of each membrane 26 is provided with a number of heat exchange elements 14, separated from one another by a short opening. This opening also serves as a form of conducting bridge to minimize heat conduction in the flow direction of the heat exchanger. The second heat exchange is arranged in a similar way. Also shown in Figure 6 is an inlet extension 38 (partially cut-away) and an outlet extension 40 for the interior of the tubular structure 32. Both extensions 38, 40 are formed from sections of the membranes 26 without heat exchange elements. . A mesh 40 is also shown between the two constructions 25. The mesh 40 serves to improve the structural stability and can be provided with holes to allow flow through it within the interior of the tubular structure 32. In use as a cooler of dew point, one or more tubular structures 32 are located within a suitable housing having an entrance communicating with the entrance extension and an exit communicating with the exit extension. The flow C through the tubular structure 32 can be induced by a fan provided in the inlet although other means of induction of flow can also be used. By providing, for example, a flow restriction at the outlet and a connection between the outlet extension and the outside of the tubular structure 32, it can be caused that a portion of the flow D recirculates countercurrently on the outside of the tubular structure 32. The rest of the flow E comes out at the exit to cool the desired space. The liquid such as water supplied to the liquid retention layer 4 by known water supply means will then be evaporated in the recirculating flow D which provides the necessary cooling to the flow C within the tubular structure 32. The recirculating flow D can then be escape through an additional escape opening provided in the accommodation. A slight adaptation can be made for use also as a heat recovery device. The housing can then be provided with an additional inlet and possibly a second fan or other flow induction device. Any flow that is proposed to be heated may also be provided with water supply to an appropriate liquid retention layer for humidification purposes. For heat recovery it is also particularly advantageous to provide both sides of the exchanger with laminates comprising liquid retention layers according to the present invention, whereby the condensation is retained and can be drained with a wick. Although not shown, the heat-exchange laminate formed by itself can be used both as a fin and as an impermeable membrane. Accordingly, a pair of heat exchange elements similar to Figure 4 but without open shutters can be connected back to back in the manner shown in Figure 6 to produce a tubular structure. While the foregoing examples illustrate the preferred embodiments of the present invention, it is noted that various other arrangements may also be considered which fall within the spirit and scope of the present invention as defined by the appended claims. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (19)

CLAIMS Having described the invention as above, the contents of the following claims are claimed as property:

1. Dew point cooler, characterized in that it comprises a heat exchange element, the dew point cooler operates in countercurrent where a product air stream flows on a first side of the heat exchange element and is cooled by transfer of heat. heat to the element and wherein a portion of the product air stream is diverted back onto a second side of the heat exchange element, the second side of the heat exchange element is provided with a water supply whereby the heat transfer from the exchange element to the water causes it to evaporate in the air stream, where the heat exchange element comprises a membrane and a formed heat exchange laminate is attached to the membrane, the exchange laminate heat formed comprises a formable carrier layer at least partially covered with a flexible liquid retention layer having a structure ab Thus, in use, a heat exchange medium can make contact directly with the carrier layer through the open structure of the liquid retention layer.

2. Dew point cooler according to claim 1, characterized in that the liquid retention layer is a fibrous material and the open structure comprises spaces between the fibers.

3. Dew point cooler according to claim 2, characterized in that the fibrous material is adhered to the carrier layer by an adhesive.

4. Dew point cooler according to claim 3, characterized in that the fibrous material comprises a bonded blend of polyester and viscose fibers.

5. Dew point cooler according to claim 3, characterized in that the fibrous material comprises a fibrous woven or woven layer.

6. Dew point cooler according to any preceding claim, characterized in that the carrier layer comprises aluminum.

7. Dew point cooler according to any preceding claim, characterized in that the liquid retention layer has an average thickness of less than 50 microns.

8. Dew point cooler according to any preceding claim, characterized in that the heat exchange laminate is corrugated to form a series of elongated fins.

9. Dew point cooler according to claim 8, characterized in that the elongated fins are in wave form in their elongated direction.

10. Dew point cooler according to claim 1, characterized in that the fins are provided with shutters.

11. Dew point cooler according to any preceding claim, characterized in that the liquid retention layer is substantially provided only on a first side of the carrier layer.

12. Dew point cooler according to any preceding claim, characterized in that the formed heat exchange laminate is bonded to the membrane by adhesive.

13. Dewpoint cooler according to claim 12, characterized in that the adhesive is a heat-activated adhesive applied to the carrier layer or the membrane.

14. Dew point cooler according to any preceding claim, characterized in that the membrane is formed in a tubular structure.

15. Dew point cooler according to any preceding claim, characterized in that the membrane also comprises a heat exchange laminate according to any of claims 1 to 7.

16. Manufacturing method of a dew point cooler, characterized in that it comprises: providing a heat exchange laminate comprising a formable carrier layer at least partially covered with a flexible liquid retention layer having an open structure; forming the laminate into a plurality of elongated fins; and joining the fins to a first surface of a membrane to transfer heat thereto to form a heat exchange element. Method according to claim 16, characterized in that it additionally comprises forming shutters in the fins. 18. Method according to claim 16, characterized in that it additionally comprises joining additional fins to a second surface of the membrane to transfer heat thereto. 19. Method according to claim 18, characterized in that it additionally comprises bending the membrane to form a tubular structure with the elongated fins on an outer surface of the tubular structure and the additional fins on an inner surface of the tubular structure.