US20090007583A1 - Evaporative Cooling Device - Google Patents
Evaporative Cooling Device Download PDFInfo
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- US20090007583A1 US20090007583A1 US12/158,752 US15875206A US2009007583A1 US 20090007583 A1 US20090007583 A1 US 20090007583A1 US 15875206 A US15875206 A US 15875206A US 2009007583 A1 US2009007583 A1 US 2009007583A1
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D5/00—Heat-exchange apparatus having stationary conduit assemblies for one heat-exchange medium only, the media being in contact with different sides of the conduit wall, using the cooling effect of natural or forced evaporation
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F1/00—Room units for air-conditioning, e.g. separate or self-contained units or units receiving primary air from a central station
- F24F1/0007—Indoor units, e.g. fan coil units
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F1/00—Room units for air-conditioning, e.g. separate or self-contained units or units receiving primary air from a central station
- F24F1/0007—Indoor units, e.g. fan coil units
- F24F1/0071—Indoor units, e.g. fan coil units with means for purifying supplied air
- F24F1/0076—Indoor units, e.g. fan coil units with means for purifying supplied air by electric means, e.g. ionisers or electrostatic separators
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F5/00—Air-conditioning systems or apparatus not covered by F24F1/00 or F24F3/00, e.g. using solar heat or combined with household units such as an oven or water heater
- F24F5/0007—Air-conditioning systems or apparatus not covered by F24F1/00 or F24F3/00, e.g. using solar heat or combined with household units such as an oven or water heater cooling apparatus specially adapted for use in air-conditioning
- F24F5/0035—Air-conditioning systems or apparatus not covered by F24F1/00 or F24F3/00, e.g. using solar heat or combined with household units such as an oven or water heater cooling apparatus specially adapted for use in air-conditioning using evaporation
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D9/00—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
- F28D9/0031—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits for one heat-exchange medium being formed by paired plates touching each other
- F28D9/0037—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits for one heat-exchange medium being formed by paired plates touching each other the conduits for the other heat-exchange medium also being formed by paired plates touching each other
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D9/00—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
- F28D9/0062—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits for one heat-exchange medium being formed by spaced plates with inserted elements
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
- F28F13/02—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by influencing fluid boundary
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F3/00—Plate-like or laminated elements; Assemblies of plate-like or laminated elements
- F28F3/02—Elements or assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with recesses, with corrugations
- F28F3/025—Elements or assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with recesses, with corrugations the means being corrugated, plate-like elements
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F3/00—Plate-like or laminated elements; Assemblies of plate-like or laminated elements
- F28F3/08—Elements constructed for building-up into stacks, e.g. capable of being taken apart for cleaning
- F28F3/086—Elements constructed for building-up into stacks, e.g. capable of being taken apart for cleaning having one or more openings therein forming tubular heat-exchange passages
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F2245/00—Coatings; Surface treatments
- F28F2245/02—Coatings; Surface treatments hydrophilic
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F2250/00—Arrangements for modifying the flow of the heat exchange media, e.g. flow guiding means; Particular flow patterns
- F28F2250/10—Particular pattern of flow of the heat exchange media
- F28F2250/104—Particular pattern of flow of the heat exchange media with parallel flow
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
- Y02B30/54—Free-cooling systems
Definitions
- the present invention relates to heat exchange devices and more particularly to evaporative cooling devices of the type that can cool a primary or product air stream by evaporation of a fluid into a secondary or working air stream. Such devices can also operate to provide heat recovery in combination with ventilation.
- An evaporative cooler is a device that uses the latent heat of evaporation of a liquid to provide cooling.
- the principle of evaporative cooling has been known for many centuries. For example, a damp cloth placed over an object will keep the object cool by evaporation of liquid from the cloth. By continuously adding liquid to the cloth, the cooling effect may be maintained indefinitely without input of electrical energy. The lowest temperature that can be reached by evaporation of moisture in this way into an air stream defines the wet-bulb temperature for that air.
- An indirect evaporative cooler makes use of this principle.
- a product air stream passing over a primary surface of a heat exchange element may be cooled by a working air stream passing over and absorbing moisture from a secondary wetted surface of the heat exchanger.
- a particularly convenient way of cooling the working air stream is to feedback a portion of the cooled product air.
- Such devices are often referred to as dew point coolers as they may lower the temperature of the product air to below its wet bulb temperature and close to the dew point.
- dew point coolers By optimising the surfaces with which the air streams exchange heat, highly effective heat transfer can be achieved. This has been found especially significant in the case of the heat transfer from the wetted secondary surface.
- the wetted secondary surface may be provided with some form of liquid supply e.g. in the form of a hydrophilic layer. The presence of such a layer can however result in increased thermal isolation of the secondary surface from the working air stream, thus reducing heat transfer.
- dew point cooler A particularly efficient form of dew point cooler is known from PCT publication WO03/091633, the contents of which are hereby incorporated by reference in their entirety.
- the device uses a membrane having heat transfer elements on its primary and secondary surfaces. These heat transfer elements are in the form of fins and are believed to improve transmission of heat from the primary surface to the secondary surface.
- the fins act both to directly conduct heat to the membrane and also to break up the various boundary layers that develop in the flow. They also serve to increase the total area available for heat exchange on the relevant surfaces.
- Further important features of the wetted second surface are known from that document and also from PCT publication WO05/019739, the contents of which are also incorporated by reference in their entirety. Accordingly, by careful choice of the material used as a water retaining layer, optimal evaporation may be achieved without thermal isolation of the secondary surface from the working air stream.
- Metals are generally good conductors of heat and a device described in PCT publication WO04/040219 uses a heat sealable metal laminate for forming both the fins and the membrane. These are then heat sealed together. Nevertheless, the adhesive component of the laminate is believed to adversely affect the heat transfer between the fins on opposite membrane surfaces. Furthermore, during the process of connection, the area of the fins actually pressed into engagement with the membrane is generally less than desired. It should also be noted in this context that heat transfer along the membrane is undesired as it can adversely affect the temperature drop between inlet and outlet. For this reason, metal membranes have in the past generally been avoided in dew point cooling devices.
- an evaporative cooling device comprising a pair of heat conducting plates arranged in spaced, generally parallel relationship and spacing elements separating the plates from one another and defining primary and secondary flow channels between the plates.
- a primary inlet duct forming an inlet fluid connection to supply air to a set of primary flow channels and a secondary inlet duct forming an inlet fluid connection to supply air to a set of secondary channels.
- the inlet ducts may be formed by the plates themselves or by additional elements.
- There may furthermore be provided a water distribution system to provide water to the secondary channels in order to wet the walls thereof. In this manner a primary air flow through the primary channels may be cooled by heat conduction along the plates to cause evaporation of the water into a secondary air flow through the secondary channels.
- reference to primary and secondary channels is, unless otherwise specified, intended to cover both the channels in their entirety and also individual channel segments within the device.
- the conducting plates may comprise boundary layer disrupting formations.
- boundary layer disrupting formations Such formations or elements are important in preventing the build up of laminar flow along the channels, in particular the secondary channels.
- Laminar flow is generally undesirable for good heat transfer from the surface of the plate.
- boundary layers By disrupting the boundary layers, local turbulent flow and better mixing of the saturated air may be encouraged, leading to a higher heat transfer coefficient.
- turbulent flow throughout the heat exchanger is usually undesirable, as the increase in pressure drop through the channel would outweigh the benefits due to increased heat transfer.
- the formations may be provided on the surfaces of the plates or may be formed by local distortions or contours of the plates themselves.
- the device comprises a plurality of heat conducting plates stacked in spaced, generally parallel relationship.
- the spacing elements define primary and secondary flow regions between or through each adjacent pair of plates. In this manner a large number of flow channels can be built up in a simple manner.
- the primary flow region between a first pair of plates is generally aligned with an adjacent primary flow region between an adjacent pair of plates.
- openings may be provided in the plates for directing flow through the plates between adjacent primary flow channels respectively and adjacent secondary flow channels respectively.
- the openings may have a number of important functions. Firstly, they can act to disrupt boundary layers and break up local laminar flow, thus increasing the heat transfer coefficient.
- the openings are preferably in the form of louvres or similar flow directing vents. Louvres have been found to be most effective in directing saturated air away from the boundary layer and into the interior of the channels, while minimising pressure drop due to excess turbulence.
- the flow channels are all generally aligned with the plates and the direction of flow in the primary channels is counter to the flow in the secondary channels. Counter flow configuration has been recognised as the most optimum for efficient dew point cooling.
- the direction of flow in the primary channels is counter to the flow in the secondary channels and generally perpendicular to a main plane of the plates.
- Such a configuration can be achieved if the louvres or openings through the plates are sufficiently large to allow flow to take place through the plates.
- a significant advantage of such a configuration is that the spacing elements may act as conduction barriers, preventing heat conduction in the direction of the primary flow. This configuration may also be advantageous in providing inlet and outlet connections for the primary and secondary flows.
- the direction of flow in the primary channels may be generally perpendicular to the flow in the secondary channels.
- the device will then operate in cross flow.
- One of the flows may be parallel to the plates and the other flow may take advantage of openings or louvres to pass through the plates.
- both flows may be partially through and partially parallel to the plates. It is noted that a considerable advantage of the present invention is the versatility that it provides in allowing different flow configurations.
- the device further comprises a hydrophilic layer at least partially covering the plates in the secondary flow channels.
- the hydrophilic layer acts as a water retaining and releasing layer.
- reference to water is understood to cover any other evaporative fluid that may be used in the operation of the device as an evaporative cooler.
- the hydrophilic layer is provided on one surface of the plate only.
- the hydrophilic layer need not be a separate layer but may also be formed as a surface treatment of the plate to improve its hydrophilicity. Cementitious materials such as Portland cement have in the past been found highly desirable. Alternatively, fibre materials may be used. It has been found to be of great importance that the water retaining layer should not obstruct heat transfer from the plate by insulating it from the secondary flow.
- the spacing elements comprise thermally insulating material.
- the spacing elements may thus be considered to form a dividing membrane between the primary and secondary flow regions. They do not however function as a heat exchange membrane as in prior art constructions.
- the spacing elements also have a constructive function in ensuring adequate support for the plates.
- the spacing elements may comprise portions of the plates extending generally perpendicular to a main plane of the plates.
- Each spacing element may support on an adjacent plate either directly or with the interpolation of an adhesive or other form of connecting element.
- the connecting element may partially assume the role of spacer and may also provide an insulating function between adjacent plates.
- the spacing elements may be provided to reduce heat conduction in the direction of the primary flow. This of course depends on the direction chosen for the primary flow.
- the conduction barriers may be provided by louvres or by other small slits. In particular, narrow slits that do not allow flow to pass but nevertheless disrupt the heat conduction may be employed.
- the plates should be good thermal conductors.
- the plates comprise aluminium, which is also light and easy to fabricate.
- the plates may also comprise other metals, in particular as alloys.
- the plate may if necessary be provided with protective layers e.g. to prevent corrosion or fouling. Nevertheless, such layers should not unduly inhibit heat transfer to the plate.
- outlets from the primary channels are in fluid connection with inlets to the secondary channels.
- part of the flow through the primary channels may be subsequently directed through the secondary channels.
- Operation in this manner as a dew point cooler is believed to be beneficial in achieving the highest efficiency of operation and the lowest outlet temperature from the primary channels.
- the fluid connection between primary outlet and secondary inlet may be on a one to one basis with one primary channel providing inlet flow to one secondary channel.
- the combined primary flow may be split and a part thereof returned and distributed to the secondary channels.
- certain primary channels may be directed exclusively to providing secondary air to all of the secondary channels.
- outlets from the primary channels is intended to include any suitable connection, whether internal or external that can deliver part of the primary flow to supply flow through the secondary channels.
- an evaporative cooler comprising a heat exchanger as described above having a housing for receiving the heat exchanger, inlet ducts connecting to the primary channels, outlet ducts connecting from the primary and secondary channels, an air circulation device for causing circulation of air through the primary and secondary channels, a water supply providing water to the water distribution system and a controller for controlling operation of the cooler.
- a dew point cooler may then operate as a stand alone device or may be integrated into a larger heating and ventilation system. Additionally, temperature, pressure, humidity and other such sensors may be provided within the housing for monitoring operation and where necessary providing feedback to the controller.
- FIG. 1A shows a perspective view of part of a conventional evaporative heat exchanger
- FIG. 1B shows a cross-sectional detail of part of FIG. 1A taken along line 1 B- 1 B;
- FIG. 2 shows a cross-sectional detail, similar to FIG. 1B , of a heat exchange element according to a first embodiment of the present invention
- FIG. 3 shows a perspective view of the heat exchange element of FIG. 2 constructed as a dew point cooling device
- FIG. 4 shows a perspective view of a second embodiment of the invention, similar to the embodiment of FIG. 3 ;
- FIG. 5 shows a perspective view of an alternative heat exchange plate for use in a third embodiment of the invention
- FIG. 6 shows a detail similar to FIG. 2 , of a fourth embodiment of the invention.
- FIG. 7 shows an end view of a fifth embodiment of the invention.
- FIG. 1A shows a section of a heat exchange element 1 of the type presently used in the prior art heat exchanger described in PCT publication WO04/040219, the content of which is hereby incorporated by reference in its entirety.
- the heat exchange element 1 comprises a membrane 10 having a first surface 12 and a second surface 14 .
- Arrows A and B give an indication of the direction of air flows for use as a dew point cooler.
- Arrow A represents the flow of primary air over the first surface 12 .
- Arrow B represents the flow of secondary air over the second surface 14 .
- the membrane 10 is formed from a thin gauge aluminium sheet. Both sides of the membrane 10 are provided with fins 16 arranged in strips 18 . The fins 16 are affixed at their bases 28 to the membrane 10 by heat seal adhesive.
- the fins 16 are also formed from aluminium laminated with a heat seal adhesive.
- heat exchange takes place primarily on the surfaces of the fins 16 on the second surface 14 rather than at the membrane itself. This heat is supplied by conduction within the material of the fins 16 from the fins on the first surface 12 .
- the fins 16 are provided with louvres 20 in the form of elongate slots penetrating through the laminate.
- the louvres 20 are arranged in groups.
- a first group 22 serves to direct flow into the surface, while a second group 24 directs flow out of the surface.
- louvres 20 serve to increase the heat transfer coefficient by breaking up the boundary layers that develop.
- secondary air B can be caused to alternately flow over first an outer surface of the fin 16 , where it can receive moisture by evaporation from a liquid retaining layer, followed by the inner surface of the fin 16 where it can receive direct thermal energy to raise its temperature.
- Fins 16 are also provided with conduction bridges 30 . These bridges 30 are in the form of cuts through the fins 16 over substantially their whole height. They reduce unwanted transport of heat along the fins 16 in the direction of the air flow which could otherwise reduce the temperature difference between inlet and outlet.
- FIG. 1B shows the different layers forming the construction.
- the membrane 10 comprises a base layer of soft annealed aluminium 42 , layers of primer 44 applied thereto and anti-corrosive adhesive layer 46 applied thereover, activated by heat and pressure for coupling of the fins 16 .
- the fins 16 also comprise a layer of soft annealed aluminium 48 provided with layers of primer 50 .
- the fins 16 are also provided with a liquid retaining layer 26 on their outer surface, which serves to retain and subsequently release the water for evaporation.
- FIG. 2 shows a cross-section through part of a heat exchange element 100 for an evaporative cooling device according to the present invention.
- a section of the heat exchange element 100 is shown, corresponding to and in the same orientation as the device shown in FIG. 1B .
- FIG. 2 there are shown a number of heat conducting plates 102 arranged in spaced, generally parallel relationship. Spacing elements 104 separate the plates 102 from one another and define, together with the plates 102 , primary 106 and secondary 108 flow channels between the plates 102 .
- the plates 102 are formed of aluminium or another suitable heat conducting material. Unlike the fins 16 of FIG. 1 , the plates 102 are not provided with an adhesive layer or primer layer.
- the plates 102 are provided in the region of of the secondary channels 108 with a water retaining layer 110 on one of their surfaces. Louvres 112 are provided through the plates 102 in the region of the secondary channels 108 .
- the spacing elements 104 are formed of a form-stable resin material.
- the spacers 104 are heat-insulating in order to reduce heat conduction in the flow direction.
- Water or another evaporable liquid is supplied to the water retaining layer 110 by means not shown.
- a flow of secondary air B is caused to flow through secondary channel 108 .
- the louvres direct the air through the plate 102 where it is then warmed by direct heat transfer from the surface of the plate 102 .
- a flow of primary air A is caused to flow through the primary channels 106 in counter flow to the secondary flow.
- the primary flow is cooled by direct heat transfer to the plate 102 .
- the heat transferred to the plate 102 in the region of the primary channel is conducted within the plate 102 according to arrow H to the region of the secondary channel 108 . It can thus be seen that plates 102 function as heat conducting elements rather than as heat exchange membranes.
- FIG. 3 shows a perspective view of the heat exchange element 100 of FIG. 2 in which the extent of the plates 102 can be seen.
- FIG. 3 also illustrates how the heat exchange element 100 could be built up into a dew point cooler 120 . It should also be noted that the heat exchange element 100 has been rotated by 90° with respect to FIG. 2 , into its operational position.
- the plates 102 extend beyond those primary 106 and secondary 108 channels shown in FIG. 2 to further primary 106 and secondary 108 channels.
- the extent of the plates 102 in the flow direction is also indicated.
- the plates 102 of the present invention extend from one extremity of the heat exchange element 100 to the other.
- FIG. 3 for the sake of simplicity only thirty two short channels are shown, it being understood that in reality, the plates 102 may extend considerably further in all directions whereby both the length and number of the channels 106 , 108 can be greater.
- FIG. 3 also illustrates inlet ducts 114 for the primary channels 106 .
- the inlet ducts 114 are formed by the material of the spacing elements 104 extending beyond the plates 102 . This material may then be formed by suitable moulding techniques into a closed inlet duct 114 .
- the inlet ducts 114 serve to direct inlet air flow A from a circulation device 115 to the primary channels 106 and to keep it separate from the air flow B exiting the secondary channels 108 . In use, the flow B will usually be saturated with moisture and will be exhausted. It is understood that other methods of forming ducts as inlets or outlets for either the primary 106 or the secondary 108 channels may also be employed as required.
- a water distribution system 116 is also illustrated in FIG. 3 .
- the water distribution system 116 is in the form of a series of conduits 118 leading from a water supply 119 to outlets 122 for ejecting droplets 124 of water into the secondary channels 108 .
- the louvres 112 allow the droplets 124 to pass through the plates 102 to the further secondary channels located below.
- Alternative water distribution systems 116 may also be used.
- a preferred arrangement is the system presently used in the Oxycell Rooftop 400 evaporative cooler substantially as described in International Patent Publication No. WO04/076931, the content of which is hereby incorporated by reference in its entirety.
- Both the water supply 119 and the circulation device 115 are controlled by a controller 130 .
- the device may be enclosed in an appropriate housing (not shown).
- liquid retaining layer An important factor for the efficient operation of an evaporative cooler is the nature of the liquid retaining layer. Although reference is made to a liquid retaining layer, it is clearly understood that the layer is in fact a liquid retaining and releasing layer. A requirement of such a layer is that it easily gives up its water such that no resistance to evaporation is encountered. It is also important that it should distribute water quickly and effectively to all relevant surfaces. It should thus be hydrophilic without being hygroscopic, preferably retaining water primarily by surface tension effects.
- the liquid retaining layer 110 is formed from a fibrous material.
- the layer 110 is schematically illustrated to have a very open structure such that the metal of the plate 102 can be clearly seen through the spaces between the fibres of the layer 110 . This is believed to encourage direct heat transfer from the plate 102 without smothering it.
- Prior art devices using thick wicking layers have effectively insulated the heat transmitting layer preventing transfer of thermal heat.
- An exemplary material for forming the water retaining layer 110 is a 20 g/m 2 polyester/viscose 50/50 blend, available from Lantor B.V. in The Netherlands.
- Another exemplary material is a 30 g/m 2 polyamide coated polyester fibre available under the name ColbackTM from Colbond N.V. in The Netherlands. Other materials having similar properties including synthetic and natural fibres such as wool may also be used.
- the liquid retaining layer 110 may be coated or otherwise treated to provide anti bacterial or other anti fouling properties.
- the liquid retaining layer 110 may be adhesively attached to the plate 102 .
- a 2 micron layer of two-component polyurethane adhesive has been found to provide excellent results. When present as such a thin layer, its effect on heat transfer is negligible. It should furthermore be noted that the presence of the liquid retaining layer only influences heat transfer from plate 102 into the secondary flow B and does not have any significant influence on heat conduction within the plate 102 between the primary 106 and secondary 108 channels.
- the above-described fibrous layers have been found ideal for the purposes of manufacturing since they can be provided as a laminate that can be formed into louvres and other shapes in a continuous process.
- liquid retaining layers such as Portland cement may also be used and have in fact been found to provide superior properties although as yet, their production is more complex since there is a tendency to crack or flake if applied prior to forming of the heat exchange element. It is nevertheless believed that other surface finishes such as aluminium oxide may themselves be adequate for providing the water retention and wicking required.
- a primary air flow A enters inlet 114 at a temperature T 1 and flows through primary channels 106 .
- the flow A is driven by a circulation device 115 .
- the flow A is cooled by heat transfer to the plate 102 to a temperature T 2 close to its dew point.
- On exit from the primary channel 106 the cooled primary flow A is split to form a cooled product flow C and secondary flow B.
- the product flow C is delivered by appropriate ducts to wherever the cooled air is required.
- the secondary flow B is returned through the secondary channels 108 .
- the secondary flow returns, it is heated by heat transfer from the plate 102 and takes up moisture by evaporation from the water retaining layer 110 .
- the flow B On exit from the secondary channel 108 , the flow B will have returned to close to its original temperature T 1 but will be almost 100% saturated.
- the difference in enthalpy between the flows A and B represents the amount of cooling available for the product flow C.
- beat may be conducted in both directions H through the plate 102 from a primary channel 106 to the secondary channels 108 on both sides thereof. Heat can also transfer in the direction of flow, which is generally undesirable.
- the presence of louvres 112 in the secondary channels 108 reduces longitudinal heat transfer in this region. According to the embodiment of FIG. 3 , no louvres are shown in the region of the primary channels 106 . It is however understood that louvres may also be provided in this region, both for encouraging turbulence and for reducing longitudinal heat transfer.
- FIG. 4 shows an alternative embodiment of the invention corresponding closely to the arrangement of FIG. 3 . Similar elements in FIG. 4 are identified by the same reference numerals as in FIG. 3 .
- louvres 112 are also provided in the region of the primary channels 106 . In this case, the louvres 112 are sufficiently large that the complete flows A and B may pass through without substantial resistance.
- Closures 126 are applied to both ends of the flow channels 106 , 108 .
- Inlet ducts 114 are formed at the lower side of the lowermost primary channels 106 . In operation, flow of primary air A is directed upwards from the inlet ducts 114 and passes sequentially through each plate 102 through louvres 112 .
- FIG. 3 and FIG. 4 operate in counter flow. For dew point coolers this is well recognised to be the most efficient configuration. There may however be certain circumstances where cross-flow configurations are desirable. Both the arrangement of FIG. 3 and that of FIG. 4 are suitable for operation in cross flow configuration.
- the secondary flow B may take place through the louvres 110 in a direction perpendicular to the plate. In FIG. 4 , either flow could be redirected by provision of suitable inlet and outlet ducts.
- FIG. 4 shows a plate 202 with spacer elements 204 arranged on it to form primary channels 206 and secondary channels 208 .
- Plate 202 is provided with openings 212 over its surface. The material of the spacer elements 204 enters into the openings 212 to prevent leakage of air from the primary channels 206 to the secondary channels 208 .
- the spacer elements 204 on either side of the plate 202 may thus join together e.g. by melting or the like to form a substantially continuous spacer structure. As in previous examples, flow may take place generally along, or generally through the plate or even diagonally.
- the plates may also be provided with water retaining layers (not shown) as described above.
- FIG. 6 shows a cross-section through part of a heat exchange element 300 similar to that of FIG. 2 .
- the embodiment of FIG. 6 differs from that of FIG. 2 in that no louvres are provided. Instead, the plates 302 are provided with a surface profile 312 to encourage turbulent flow. In this example, the surface profile 312 is shown as small dimples. It is understood however that the plates 302 themselves may be further profiled or corrugated to achieve the desired effect.
- the water retaining layer 310 is provided in the secondary channels 308 as intermittent strips such that air flow passes alternately over the metallic surface of the plate 302 and the wetted surface of the water retaining layer 310 .
- each spacing element 304 is in the form of a small resilient tube 318 having outlets 322 . Supply of water to the tubes 318 under pressure causes drips to be ejected from the outlets 322 to wet the water retaining layer 310 .
- FIGS. 2 to 6 have used separate spacer elements to keep the plates apart.
- FIG. 7 there is shown in cross-section in FIG. 7 an embodiment in which the spacer is formed from the material of the plate itself.
- a plurality of plates 402 is formed, each having a zig-zag structure.
- Each plate 402 has primary channel regions 430 and secondary channel regions 432 separated by spacer regions 434 .
- the spacer regions 434 are generally perpendicular to the primary channel regions 430 and the secondary channel regions 432 . It is noted that the primary channel regions 430 are larger than the secondary channel regions 432 . The reason for this difference will be explained in further detail below.
- the primary and secondary channel regions 430 , 432 are provided with louvres 412 and the secondary channel regions 432 are provided with water retaining layers (not shown) as in the previous embodiments of FIGS. 2 to 5 .
- the plates 402 are stacked upon one another so that the spacer regions 434 align with one another and space each plate 402 from its neighbour.
- the points of contact between plates are connected together by adhesive 436 .
- the adhesive 436 also serves as a spacer in the manner of the previous embodiments.
- the plates may alternatively be connected together in other appropriate manners e.g. by snap mechanical connection.
- a primary air flow A flows through primary channel regions 430 .
- the flow A may be driven by an appropriate fan (not shown).
- the flow A is cooled by heat transfer to the plate 402 .
- On exit from the primary channel regions 430 the cooled primary flow A is split to form a cooled product flow C and secondary flow B.
- the secondary flow B is returned through the secondary channel regions 432 .
- As the secondary flow returns it is heated by heat transfer from the plate 402 and takes up moisture by evaporation from the water retaining layer. Since only part of the flow returns through the secondary channel regions, their cross-sectional area need not be as great as the primary channel regions. Such differences in flow area between primary and secondary channels may also be employed in the earlier embodiments.
- the flows A, B may take place through the plates 402 by passing through the louvres 410 .
- the adhesive 436 acts as a thermal spacer or bridge, preventing conduction in the direction of the flow.
- the flows A, B may also take place generally along the plates 402 whereby only a portion of the flow passes through the louvres 410 .
Abstract
Description
- 1. Field of the Invention
- The present invention relates to heat exchange devices and more particularly to evaporative cooling devices of the type that can cool a primary or product air stream by evaporation of a fluid into a secondary or working air stream. Such devices can also operate to provide heat recovery in combination with ventilation.
- 2. Description of the Related Art
- An evaporative cooler is a device that uses the latent heat of evaporation of a liquid to provide cooling. The principle of evaporative cooling has been known for many centuries. For example, a damp cloth placed over an object will keep the object cool by evaporation of liquid from the cloth. By continuously adding liquid to the cloth, the cooling effect may be maintained indefinitely without input of electrical energy. The lowest temperature that can be reached by evaporation of moisture in this way into an air stream defines the wet-bulb temperature for that air. An indirect evaporative cooler makes use of this principle. A product air stream passing over a primary surface of a heat exchange element may be cooled by a working air stream passing over and absorbing moisture from a secondary wetted surface of the heat exchanger.
- According to theory, if a quantity of air is cooled by direct evaporation its absolute humidity increases due to the uptake of moisture. Its relative humidity also increases due to its lowered temperature until at the wet bulb temperature it is fully saturated with water vapour. If the air is cooled without direct evaporation however, its absolute humidity remains the same. As its temperature decreases only the relative humidity increases until full saturation of the air is reached at the so-called dew point. The dew point is thus lower than the wet bulb temperature and is in fact defined as the temperature to which a body of air must be cooled to reach saturation or 100% relative humidity. At this point, water vapour in the air condenses.
- Attempts have been made to improve on the principle of indirect evaporative cooling by cooling or drying the working air stream prior to evaporation taking place. A particularly convenient way of cooling the working air stream is to feedback a portion of the cooled product air. Such devices are often referred to as dew point coolers as they may lower the temperature of the product air to below its wet bulb temperature and close to the dew point. By optimising the surfaces with which the air streams exchange heat, highly effective heat transfer can be achieved. This has been found especially significant in the case of the heat transfer from the wetted secondary surface. In order to provide moisture to the working air stream, the wetted secondary surface may be provided with some form of liquid supply e.g. in the form of a hydrophilic layer. The presence of such a layer can however result in increased thermal isolation of the secondary surface from the working air stream, thus reducing heat transfer.
- A particularly efficient form of dew point cooler is known from PCT publication WO03/091633, the contents of which are hereby incorporated by reference in their entirety. The device uses a membrane having heat transfer elements on its primary and secondary surfaces. These heat transfer elements are in the form of fins and are believed to improve transmission of heat from the primary surface to the secondary surface. The fins act both to directly conduct heat to the membrane and also to break up the various boundary layers that develop in the flow. They also serve to increase the total area available for heat exchange on the relevant surfaces. Further important features of the wetted second surface are known from that document and also from PCT publication WO05/019739, the contents of which are also incorporated by reference in their entirety. Accordingly, by careful choice of the material used as a water retaining layer, optimal evaporation may be achieved without thermal isolation of the secondary surface from the working air stream.
- The driving temperature differential between the primary and secondary flows of an evaporative cooler of this type must be very low in order to achieve cooling down to the dew point. As a consequence, in order for good heat transfer to occur, the heat conduction coefficient across the heat exchanger must be high. In the case of WO03/091633, the point of attachment of the fins to the membrane is believed to be an area of poor heat transmission. According to PCT publication WO 03/091648 A, attempts have been made to improve heat transmission by connecting the fins on opposing sides of a membrane directly through the membrane. According to PCT publication WO 01/57461, the fins are formed as convolutions in the membrane itself.
- Metals are generally good conductors of heat and a device described in PCT publication WO04/040219 uses a heat sealable metal laminate for forming both the fins and the membrane. These are then heat sealed together. Nevertheless, the adhesive component of the laminate is believed to adversely affect the heat transfer between the fins on opposite membrane surfaces. Furthermore, during the process of connection, the area of the fins actually pressed into engagement with the membrane is generally less than desired. It should also be noted in this context that heat transfer along the membrane is undesired as it can adversely affect the temperature drop between inlet and outlet. For this reason, metal membranes have in the past generally been avoided in dew point cooling devices.
- Many other configurations have also been suggested for evaporative cooling devices, all of which require heat transfer through a membrane. The membrane divides the wet region, where liquid is provided for evaporation, from the dry region. A number of constructions by Maisotsenko et al are shown in U.S. Pat. No. 6,581,402, in which primary and working streams across a plate are separated by channel guides. The secondary stream is diverted to the opposite side of the plate and receives heat by evaporation and by heat transfer from the plate.
- In order to improve heat transmission between a primary and secondary flow, there is provided according to the invention an evaporative cooling device comprising a pair of heat conducting plates arranged in spaced, generally parallel relationship and spacing elements separating the plates from one another and defining primary and secondary flow channels between the plates. In this manner, heat transmission between the primary and secondary channels can take place primarily by conduction along the plates from the region associated with the primary channels to the regions associated with the secondary channels. This is in contrast to conventional arrangements where heat transfer between fluids takes place through a membrane separating the fluids. In order to direct the first and second flows, there may be provided a primary inlet duct forming an inlet fluid connection to supply air to a set of primary flow channels and a secondary inlet duct forming an inlet fluid connection to supply air to a set of secondary channels. The inlet ducts may be formed by the plates themselves or by additional elements. There may furthermore be provided a water distribution system to provide water to the secondary channels in order to wet the walls thereof. In this manner a primary air flow through the primary channels may be cooled by heat conduction along the plates to cause evaporation of the water into a secondary air flow through the secondary channels. In the present context, reference to primary and secondary channels is, unless otherwise specified, intended to cover both the channels in their entirety and also individual channel segments within the device.
- According to a further embodiment of the invention, the conducting plates may comprise boundary layer disrupting formations. Such formations or elements are important in preventing the build up of laminar flow along the channels, in particular the secondary channels. Laminar flow is generally undesirable for good heat transfer from the surface of the plate. By disrupting the boundary layers, local turbulent flow and better mixing of the saturated air may be encouraged, leading to a higher heat transfer coefficient. It is noted that turbulent flow throughout the heat exchanger is usually undesirable, as the increase in pressure drop through the channel would outweigh the benefits due to increased heat transfer. The formations may be provided on the surfaces of the plates or may be formed by local distortions or contours of the plates themselves.
- Preferably the device comprises a plurality of heat conducting plates stacked in spaced, generally parallel relationship. The spacing elements define primary and secondary flow regions between or through each adjacent pair of plates. In this manner a large number of flow channels can be built up in a simple manner.
- Most preferably, for such a stacked plate construction, the primary flow region between a first pair of plates is generally aligned with an adjacent primary flow region between an adjacent pair of plates. In this case openings may be provided in the plates for directing flow through the plates between adjacent primary flow channels respectively and adjacent secondary flow channels respectively. The openings may have a number of important functions. Firstly, they can act to disrupt boundary layers and break up local laminar flow, thus increasing the heat transfer coefficient. Secondly, by directing the secondary flow over both surfaces of the plate, if water or a water retaining layer is provided on one of the surfaces, the secondary flow can be alternately exposed to thermal heat transfer and latent heat. The openings are preferably in the form of louvres or similar flow directing vents. Louvres have been found to be most effective in directing saturated air away from the boundary layer and into the interior of the channels, while minimising pressure drop due to excess turbulence.
- According to a first embodiment of the invention the flow channels are all generally aligned with the plates and the direction of flow in the primary channels is counter to the flow in the secondary channels. Counter flow configuration has been recognised as the most optimum for efficient dew point cooling.
- According to a second embodiment of the invention the direction of flow in the primary channels is counter to the flow in the secondary channels and generally perpendicular to a main plane of the plates. Such a configuration can be achieved if the louvres or openings through the plates are sufficiently large to allow flow to take place through the plates. A significant advantage of such a configuration is that the spacing elements may act as conduction barriers, preventing heat conduction in the direction of the primary flow. This configuration may also be advantageous in providing inlet and outlet connections for the primary and secondary flows.
- In an alternative embodiment, the direction of flow in the primary channels may be generally perpendicular to the flow in the secondary channels. The device will then operate in cross flow. One of the flows may be parallel to the plates and the other flow may take advantage of openings or louvres to pass through the plates. Alternatively, both flows may be partially through and partially parallel to the plates. It is noted that a considerable advantage of the present invention is the versatility that it provides in allowing different flow configurations.
- According to an important feature of the invention, the device further comprises a hydrophilic layer at least partially covering the plates in the secondary flow channels. The hydrophilic layer acts as a water retaining and releasing layer. In this context, reference to water is understood to cover any other evaporative fluid that may be used in the operation of the device as an evaporative cooler. Most preferably, the hydrophilic layer is provided on one surface of the plate only. The hydrophilic layer need not be a separate layer but may also be formed as a surface treatment of the plate to improve its hydrophilicity. Cementitious materials such as Portland cement have in the past been found highly desirable. Alternatively, fibre materials may be used. It has been found to be of great importance that the water retaining layer should not obstruct heat transfer from the plate by insulating it from the secondary flow.
- In a preferred embodiment, the spacing elements comprise thermally insulating material. The spacing elements may thus be considered to form a dividing membrane between the primary and secondary flow regions. They do not however function as a heat exchange membrane as in prior art constructions. The spacing elements also have a constructive function in ensuring adequate support for the plates.
- In an alternative embodiment, the spacing elements may comprise portions of the plates extending generally perpendicular to a main plane of the plates. Each spacing element may support on an adjacent plate either directly or with the interpolation of an adhesive or other form of connecting element. In this case, the connecting element may partially assume the role of spacer and may also provide an insulating function between adjacent plates.
- Although a function of the spacing elements has been described as providing insulation between plates, other forms of conduction barriers may be provided to reduce heat conduction in the direction of the primary flow. This of course depends on the direction chosen for the primary flow. For flow along the plates, the conduction barriers may be provided by louvres or by other small slits. In particular, narrow slits that do not allow flow to pass but nevertheless disrupt the heat conduction may be employed.
- According to an important aspect of the invention, the plates should be good thermal conductors. Preferably the plates comprise aluminium, which is also light and easy to fabricate. The plates may also comprise other metals, in particular as alloys. The plate may if necessary be provided with protective layers e.g. to prevent corrosion or fouling. Nevertheless, such layers should not unduly inhibit heat transfer to the plate.
- According to a preferred embodiment of the invention, outlets from the primary channels are in fluid connection with inlets to the secondary channels. In this manner part of the flow through the primary channels may be subsequently directed through the secondary channels. Operation in this manner as a dew point cooler is believed to be beneficial in achieving the highest efficiency of operation and the lowest outlet temperature from the primary channels. The fluid connection between primary outlet and secondary inlet may be on a one to one basis with one primary channel providing inlet flow to one secondary channel. Alternatively, the combined primary flow may be split and a part thereof returned and distributed to the secondary channels. In a further alternative, certain primary channels may be directed exclusively to providing secondary air to all of the secondary channels. In this context, reference to outlets from the primary channels is intended to include any suitable connection, whether internal or external that can deliver part of the primary flow to supply flow through the secondary channels.
- According to a yet further aspect of the invention, there is provided an evaporative cooler comprising a heat exchanger as described above having a housing for receiving the heat exchanger, inlet ducts connecting to the primary channels, outlet ducts connecting from the primary and secondary channels, an air circulation device for causing circulation of air through the primary and secondary channels, a water supply providing water to the water distribution system and a controller for controlling operation of the cooler. Such a dew point cooler may then operate as a stand alone device or may be integrated into a larger heating and ventilation system. Additionally, temperature, pressure, humidity and other such sensors may be provided within the housing for monitoring operation and where necessary providing feedback to the controller.
- The features and advantages of the invention will be appreciated upon reference to the following drawings of a number of exemplary embodiments, in which:
-
FIG. 1A shows a perspective view of part of a conventional evaporative heat exchanger; -
FIG. 1B shows a cross-sectional detail of part ofFIG. 1A taken alongline 1B-1B; -
FIG. 2 shows a cross-sectional detail, similar toFIG. 1B , of a heat exchange element according to a first embodiment of the present invention; -
FIG. 3 shows a perspective view of the heat exchange element ofFIG. 2 constructed as a dew point cooling device; -
FIG. 4 shows a perspective view of a second embodiment of the invention, similar to the embodiment ofFIG. 3 ; -
FIG. 5 shows a perspective view of an alternative heat exchange plate for use in a third embodiment of the invention; -
FIG. 6 shows a detail similar toFIG. 2 , of a fourth embodiment of the invention; and -
FIG. 7 shows an end view of a fifth embodiment of the invention. -
FIG. 1A shows a section of a heat exchange element 1 of the type presently used in the prior art heat exchanger described in PCT publication WO04/040219, the content of which is hereby incorporated by reference in its entirety. The heat exchange element 1 comprises amembrane 10 having afirst surface 12 and asecond surface 14. Arrows A and B give an indication of the direction of air flows for use as a dew point cooler. Arrow A represents the flow of primary air over thefirst surface 12. Arrow B represents the flow of secondary air over thesecond surface 14. Themembrane 10 is formed from a thin gauge aluminium sheet. Both sides of themembrane 10 are provided withfins 16 arranged instrips 18. Thefins 16 are affixed at theirbases 28 to themembrane 10 by heat seal adhesive. To this end, thefins 16 are also formed from aluminium laminated with a heat seal adhesive. In evaporative cooling devices of this type, heat exchange takes place primarily on the surfaces of thefins 16 on thesecond surface 14 rather than at the membrane itself. This heat is supplied by conduction within the material of thefins 16 from the fins on thefirst surface 12. - The
fins 16 are provided withlouvres 20 in the form of elongate slots penetrating through the laminate. Thelouvres 20 are arranged in groups. Afirst group 22 serves to direct flow into the surface, while asecond group 24 directs flow out of the surface. By directing flow in this manner between both surfaces of thefins 16,louvres 20 serve to increase the heat transfer coefficient by breaking up the boundary layers that develop. In addition to this function, on thesecond surface 14 secondary air B can be caused to alternately flow over first an outer surface of thefin 16, where it can receive moisture by evaporation from a liquid retaining layer, followed by the inner surface of thefin 16 where it can receive direct thermal energy to raise its temperature.Fins 16 are also provided with conduction bridges 30. Thesebridges 30 are in the form of cuts through thefins 16 over substantially their whole height. They reduce unwanted transport of heat along thefins 16 in the direction of the air flow which could otherwise reduce the temperature difference between inlet and outlet. -
FIG. 1B shows the different layers forming the construction. Themembrane 10 comprises a base layer of soft annealedaluminium 42, layers ofprimer 44 applied thereto and anti-corrosiveadhesive layer 46 applied thereover, activated by heat and pressure for coupling of thefins 16. Thefins 16 also comprise a layer of soft annealedaluminium 48 provided with layers ofprimer 50. Thefins 16 are also provided with aliquid retaining layer 26 on their outer surface, which serves to retain and subsequently release the water for evaporation. - In order to function effectively as a dew point cooler, heat transmission between the
fins 16 on thefirst surface 12 and thesecond surface 14 must be maximized by ensuring appropriate joining techniques. In order to also maximise the area of heat transfer through themembrane 10, the base ortrough 28 of thefins 16 must be made as wide and as flat as possible. It has however been found, that despite great care in joining thefins 16 to themembrane 10, the area of contact is not sufficient. Furthermore, the presence of adhesives and primers in the fin/membrane/fin construction has reduced the coefficient of heat transfer across the membrane. -
FIG. 2 shows a cross-section through part of aheat exchange element 100 for an evaporative cooling device according to the present invention. In order to allow direct comparison with the prior art arrangement, only a section of theheat exchange element 100 is shown, corresponding to and in the same orientation as the device shown inFIG. 1B . - According to
FIG. 2 , there are shown a number ofheat conducting plates 102 arranged in spaced, generally parallel relationship. Spacingelements 104 separate theplates 102 from one another and define, together with theplates 102, primary 106 and secondary 108 flow channels between theplates 102. Theplates 102 are formed of aluminium or another suitable heat conducting material. Unlike thefins 16 ofFIG. 1 , theplates 102 are not provided with an adhesive layer or primer layer. Theplates 102 are provided in the region of of thesecondary channels 108 with awater retaining layer 110 on one of their surfaces.Louvres 112 are provided through theplates 102 in the region of thesecondary channels 108. Thespacing elements 104 are formed of a form-stable resin material. There is no requirement for them to be heat conductive, as their function is only to maintain theplates 102 in spaced relation and prevent air flow from theprimary channels 106 to thesecondary channels 108. It is in fact believed to be desirable that thespacers 104 are heat-insulating in order to reduce heat conduction in the flow direction. - Operation of the device according to
FIG. 2 will now be explained in further detail. Water or another evaporable liquid is supplied to thewater retaining layer 110 by means not shown. A flow of secondary air B is caused to flow throughsecondary channel 108. As the secondary air passes over the water retaining layer, it takes up water by evaporation. The louvres direct the air through theplate 102 where it is then warmed by direct heat transfer from the surface of theplate 102. A flow of primary air A is caused to flow through theprimary channels 106 in counter flow to the secondary flow. The primary flow is cooled by direct heat transfer to theplate 102. The heat transferred to theplate 102 in the region of the primary channel is conducted within theplate 102 according to arrow H to the region of thesecondary channel 108. It can thus be seen thatplates 102 function as heat conducting elements rather than as heat exchange membranes. -
FIG. 3 shows a perspective view of theheat exchange element 100 ofFIG. 2 in which the extent of theplates 102 can be seen.FIG. 3 also illustrates how theheat exchange element 100 could be built up into adew point cooler 120. It should also be noted that theheat exchange element 100 has been rotated by 90° with respect toFIG. 2 , into its operational position. - As can be seen in
FIG. 3 , theplates 102 extend beyond those primary 106 and secondary 108 channels shown inFIG. 2 tofurther primary 106 and secondary 108 channels. The extent of theplates 102 in the flow direction is also indicated. Unlike thefins 16 of the prior art device ofFIG. 1 which were arranged instrips 18, theplates 102 of the present invention extend from one extremity of theheat exchange element 100 to the other. InFIG. 3 , for the sake of simplicity only thirty two short channels are shown, it being understood that in reality, theplates 102 may extend considerably further in all directions whereby both the length and number of thechannels -
FIG. 3 also illustratesinlet ducts 114 for theprimary channels 106. Theinlet ducts 114 are formed by the material of thespacing elements 104 extending beyond theplates 102. This material may then be formed by suitable moulding techniques into aclosed inlet duct 114. Theinlet ducts 114 serve to direct inlet air flow A from acirculation device 115 to theprimary channels 106 and to keep it separate from the air flow B exiting thesecondary channels 108. In use, the flow B will usually be saturated with moisture and will be exhausted. It is understood that other methods of forming ducts as inlets or outlets for either the primary 106 or the secondary 108 channels may also be employed as required. - A
water distribution system 116 is also illustrated inFIG. 3 . Thewater distribution system 116 is in the form of a series ofconduits 118 leading from awater supply 119 tooutlets 122 for ejectingdroplets 124 of water into thesecondary channels 108. Thelouvres 112 allow thedroplets 124 to pass through theplates 102 to the further secondary channels located below. Alternativewater distribution systems 116 may also be used. A preferred arrangement is the system presently used in the Oxycell Rooftop 400 evaporative cooler substantially as described in International Patent Publication No. WO04/076931, the content of which is hereby incorporated by reference in its entirety. Both thewater supply 119 and thecirculation device 115 are controlled by acontroller 130. The device may be enclosed in an appropriate housing (not shown). - An important factor for the efficient operation of an evaporative cooler is the nature of the liquid retaining layer. Although reference is made to a liquid retaining layer, it is clearly understood that the layer is in fact a liquid retaining and releasing layer. A requirement of such a layer is that it easily gives up its water such that no resistance to evaporation is encountered. It is also important that it should distribute water quickly and effectively to all relevant surfaces. It should thus be hydrophilic without being hygroscopic, preferably retaining water primarily by surface tension effects.
- In the embodiment of
FIGS. 2 and 3 , theliquid retaining layer 110 is formed from a fibrous material. Thelayer 110 is schematically illustrated to have a very open structure such that the metal of theplate 102 can be clearly seen through the spaces between the fibres of thelayer 110. This is believed to encourage direct heat transfer from theplate 102 without smothering it. Prior art devices using thick wicking layers have effectively insulated the heat transmitting layer preventing transfer of thermal heat. An exemplary material for forming thewater retaining layer 110 is a 20 g/m2 polyester/viscose 50/50 blend, available from Lantor B.V. in The Netherlands. Another exemplary material is a 30 g/m2 polyamide coated polyester fibre available under the name Colback™ from Colbond N.V. in The Netherlands. Other materials having similar properties including synthetic and natural fibres such as wool may also be used. Where necessary, theliquid retaining layer 110 may be coated or otherwise treated to provide anti bacterial or other anti fouling properties. - The
liquid retaining layer 110 may be adhesively attached to theplate 102. For use with aluminium and Lantor fibres as mentioned above, a 2 micron layer of two-component polyurethane adhesive has been found to provide excellent results. When present as such a thin layer, its effect on heat transfer is negligible. It should furthermore be noted that the presence of the liquid retaining layer only influences heat transfer fromplate 102 into the secondary flow B and does not have any significant influence on heat conduction within theplate 102 between the primary 106 and secondary 108 channels. The above-described fibrous layers have been found ideal for the purposes of manufacturing since they can be provided as a laminate that can be formed into louvres and other shapes in a continuous process. Other liquid retaining layers such as Portland cement may also be used and have in fact been found to provide superior properties although as yet, their production is more complex since there is a tendency to crack or flake if applied prior to forming of the heat exchange element. It is nevertheless believed that other surface finishes such as aluminium oxide may themselves be adequate for providing the water retention and wicking required. - Operation of the
device 120 as depicted inFIG. 3 in a dew point cooler configuration will now be described based on the principle described in relation toFIG. 2 . A primary air flow A entersinlet 114 at a temperature T1 and flows throughprimary channels 106. The flow A is driven by acirculation device 115. The flow A is cooled by heat transfer to theplate 102 to a temperature T2 close to its dew point. On exit from theprimary channel 106 the cooled primary flow A is split to form a cooled product flow C and secondary flow B. The product flow C is delivered by appropriate ducts to wherever the cooled air is required. The secondary flow B is returned through thesecondary channels 108. As the secondary flow returns, it is heated by heat transfer from theplate 102 and takes up moisture by evaporation from thewater retaining layer 110. On exit from thesecondary channel 108, the flow B will have returned to close to its original temperature T1 but will be almost 100% saturated. The difference in enthalpy between the flows A and B represents the amount of cooling available for the product flow C. - In the arrangement of
FIG. 3 , it is noted that beat may be conducted in both directions H through theplate 102 from aprimary channel 106 to thesecondary channels 108 on both sides thereof. Heat can also transfer in the direction of flow, which is generally undesirable. The presence oflouvres 112 in thesecondary channels 108 reduces longitudinal heat transfer in this region. According to the embodiment ofFIG. 3 , no louvres are shown in the region of theprimary channels 106. It is however understood that louvres may also be provided in this region, both for encouraging turbulence and for reducing longitudinal heat transfer. -
FIG. 4 shows an alternative embodiment of the invention corresponding closely to the arrangement ofFIG. 3 . Similar elements inFIG. 4 are identified by the same reference numerals as inFIG. 3 . According toFIG. 4 ,louvres 112 are also provided in the region of theprimary channels 106. In this case, thelouvres 112 are sufficiently large that the complete flows A and B may pass through without substantial resistance.Closures 126 are applied to both ends of theflow channels Inlet ducts 114 are formed at the lower side of the lowermostprimary channels 106. In operation, flow of primary air A is directed upwards from theinlet ducts 114 and passes sequentially through eachplate 102 throughlouvres 112. On exiting from the region of the uppermostprimary channel 106 the flow is split to form a product flow C and a secondary flow B that returns downwardly through theplates 108 in the region ofsecondary channels 108. Operation is otherwise substantially identical to that of the embodiment ofFIG. 3 . A number of advantages may however be noted. Since the flows A and B are generally normal to theplates 102, there can be no heat conduction in the direction of flow. Furthermore, since the secondary flow B is aligned with the direction of water distribution, it may be used to improve transport of water. It is noted that the direction of the flows inFIG. 4 may also be reversed whereby the primary flow A is downwards. Alternatively, the arrangement may be turned on one side and water may be supplied to thesecondary channels 108 through theclosures 126. A further advantage of the embodiment ofFIG. 4 is that theclosures 126 and inlet ducts 114 (or further ducts) may be more simple to produce and connect. - The embodiments of both
FIG. 3 andFIG. 4 operate in counter flow. For dew point coolers this is well recognised to be the most efficient configuration. There may however be certain circumstances where cross-flow configurations are desirable. Both the arrangement ofFIG. 3 and that ofFIG. 4 are suitable for operation in cross flow configuration. InFIG. 3 , the secondary flow B may take place through thelouvres 110 in a direction perpendicular to the plate. InFIG. 4 , either flow could be redirected by provision of suitable inlet and outlet ducts. - While the embodiment of
FIG. 4 has been explained with the use oflouvres 112, it is understood that any suitable passages through theplates 102 may be used. It is also noted that the louvres or passages need not be confined to the individual channel regions if the material of the spacer elements is a resin that can impregnate theplate 102 and seal such passages.FIG. 5 shows aplate 202 withspacer elements 204 arranged on it to formprimary channels 206 andsecondary channels 208.Plate 202 is provided withopenings 212 over its surface. The material of thespacer elements 204 enters into theopenings 212 to prevent leakage of air from theprimary channels 206 to thesecondary channels 208. Thespacer elements 204 on either side of theplate 202 may thus join together e.g. by melting or the like to form a substantially continuous spacer structure. As in previous examples, flow may take place generally along, or generally through the plate or even diagonally. The plates may also be provided with water retaining layers (not shown) as described above. - Many further variations of the construction can be contemplated.
FIG. 6 shows a cross-section through part of aheat exchange element 300 similar to that ofFIG. 2 . The embodiment ofFIG. 6 differs from that ofFIG. 2 in that no louvres are provided. Instead, theplates 302 are provided with asurface profile 312 to encourage turbulent flow. In this example, thesurface profile 312 is shown as small dimples. It is understood however that theplates 302 themselves may be further profiled or corrugated to achieve the desired effect. Thewater retaining layer 310 is provided in thesecondary channels 308 as intermittent strips such that air flow passes alternately over the metallic surface of theplate 302 and the wetted surface of thewater retaining layer 310. A further feature of the embodiment ofFIG. 6 is that thewater distribution system 316 is provided within thespacing elements 304. Eachspacing element 304 is in the form of a smallresilient tube 318 havingoutlets 322. Supply of water to thetubes 318 under pressure causes drips to be ejected from theoutlets 322 to wet thewater retaining layer 310. - The embodiments of
FIGS. 2 to 6 have used separate spacer elements to keep the plates apart. According to a further aspect of the invention, there is shown in cross-section inFIG. 7 an embodiment in which the spacer is formed from the material of the plate itself. According toFIG. 7 , a plurality ofplates 402 is formed, each having a zig-zag structure. Eachplate 402 hasprimary channel regions 430 andsecondary channel regions 432 separated byspacer regions 434. Thespacer regions 434 are generally perpendicular to theprimary channel regions 430 and thesecondary channel regions 432. It is noted that theprimary channel regions 430 are larger than thesecondary channel regions 432. The reason for this difference will be explained in further detail below. The primary andsecondary channel regions louvres 412 and thesecondary channel regions 432 are provided with water retaining layers (not shown) as in the previous embodiments ofFIGS. 2 to 5 . Theplates 402 are stacked upon one another so that thespacer regions 434 align with one another and space eachplate 402 from its neighbour. The points of contact between plates are connected together by adhesive 436. The adhesive 436 also serves as a spacer in the manner of the previous embodiments. The plates may alternatively be connected together in other appropriate manners e.g. by snap mechanical connection. - Operation of the embodiment of
FIG. 7 as a dew point cooler is substantially the same as that of the previous embodiments. A primary air flow A flows throughprimary channel regions 430. The flow A may be driven by an appropriate fan (not shown). The flow A is cooled by heat transfer to theplate 402. On exit from theprimary channel regions 430 the cooled primary flow A is split to form a cooled product flow C and secondary flow B. The secondary flow B is returned through thesecondary channel regions 432. As the secondary flow returns, it is heated by heat transfer from theplate 402 and takes up moisture by evaporation from the water retaining layer. Since only part of the flow returns through the secondary channel regions, their cross-sectional area need not be as great as the primary channel regions. Such differences in flow area between primary and secondary channels may also be employed in the earlier embodiments. - The flows A, B may take place through the
plates 402 by passing through the louvres 410. In such a flow configuration, the adhesive 436 acts as a thermal spacer or bridge, preventing conduction in the direction of the flow. The flows A, B may also take place generally along theplates 402 whereby only a portion of the flow passes through the louvres 410. - Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.
Claims (19)
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
NL1030739 | 2005-12-22 | ||
NL1030739 | 2005-12-22 | ||
GB0526569A GB0526569D0 (en) | 2005-12-30 | 2005-12-30 | Evaporative cooling device |
GB0526569.9 | 2005-12-30 | ||
PCT/EP2006/070205 WO2007071796A1 (en) | 2005-12-22 | 2006-12-22 | Evaporative cooling device |
Publications (1)
Publication Number | Publication Date |
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US20090007583A1 true US20090007583A1 (en) | 2009-01-08 |
Family
ID=37898362
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US12/158,752 Abandoned US20090007583A1 (en) | 2005-12-22 | 2006-12-22 | Evaporative Cooling Device |
Country Status (11)
Country | Link |
---|---|
US (1) | US20090007583A1 (en) |
EP (1) | EP1969300B1 (en) |
KR (1) | KR101497297B1 (en) |
CN (1) | CN101336358B (en) |
AU (1) | AU2006326947B2 (en) |
CA (1) | CA2635413C (en) |
IL (1) | IL192381A0 (en) |
MX (1) | MX2008008113A (en) |
MY (1) | MY151856A (en) |
RU (1) | RU2423656C2 (en) |
WO (1) | WO2007071796A1 (en) |
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CN108085078A (en) * | 2017-12-29 | 2018-05-29 | 浙江镭弘激光科技有限公司 | A kind of drawing-off gas dehydrator |
US11054157B2 (en) * | 2016-07-11 | 2021-07-06 | Oxycom Beheer B.V. | Two stage cooler |
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US11022330B2 (en) | 2018-05-18 | 2021-06-01 | Emerson Climate Technologies, Inc. | Three-way heat exchangers for liquid desiccant air-conditioning systems and methods of manufacture |
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- 2006-12-22 RU RU2008129540/06A patent/RU2423656C2/en active
- 2006-12-22 CA CA2635413A patent/CA2635413C/en active Active
- 2006-12-22 CN CN2006800522804A patent/CN101336358B/en not_active Expired - Fee Related
- 2006-12-22 MY MYPI20082288 patent/MY151856A/en unknown
- 2006-12-22 MX MX2008008113A patent/MX2008008113A/en active IP Right Grant
- 2006-12-22 KR KR1020087017652A patent/KR101497297B1/en active IP Right Grant
- 2006-12-22 WO PCT/EP2006/070205 patent/WO2007071796A1/en active Application Filing
- 2006-12-22 US US12/158,752 patent/US20090007583A1/en not_active Abandoned
- 2006-12-22 AU AU2006326947A patent/AU2006326947B2/en active Active
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US3228460A (en) * | 1963-11-18 | 1966-01-11 | Ibm | Heat exchange device |
US3912003A (en) * | 1973-04-13 | 1975-10-14 | Jean Schrade | Heat exchanger |
US4147210A (en) * | 1976-08-03 | 1979-04-03 | Pronko Vladimir G | Screen heat exchanger |
US4577678A (en) * | 1983-08-08 | 1986-03-25 | Kraftanlagen Ag | Storage material for heat transfer |
US4854129A (en) * | 1987-06-11 | 1989-08-08 | Hickley Pieter | Cooling process and apparatus |
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US11054157B2 (en) * | 2016-07-11 | 2021-07-06 | Oxycom Beheer B.V. | Two stage cooler |
CN107606721A (en) * | 2017-10-27 | 2018-01-19 | 林斯茂 | For cooling in summer, the Multifunctional air handling device of winter preheating and humidifying air |
CN108088289A (en) * | 2017-12-29 | 2018-05-29 | 浙江镭弘激光科技有限公司 | A kind of two-chamber rests the head on formula heat exchanger |
CN108085078A (en) * | 2017-12-29 | 2018-05-29 | 浙江镭弘激光科技有限公司 | A kind of drawing-off gas dehydrator |
EP4019876A1 (en) * | 2020-12-28 | 2022-06-29 | Huawei Digital Power Technologies Co., Ltd. | Heat exchanger, modular indirect evaporation cooling system, and method for controlling modular indirect evaporation cooling system |
Also Published As
Publication number | Publication date |
---|---|
EP1969300A1 (en) | 2008-09-17 |
KR20080081050A (en) | 2008-09-05 |
EP1969300B1 (en) | 2018-09-19 |
CA2635413C (en) | 2016-02-23 |
WO2007071796A1 (en) | 2007-06-28 |
CA2635413A1 (en) | 2007-06-28 |
AU2006326947B2 (en) | 2013-10-31 |
MY151856A (en) | 2014-07-14 |
RU2008129540A (en) | 2010-01-27 |
CN101336358B (en) | 2012-07-18 |
RU2423656C2 (en) | 2011-07-10 |
IL192381A0 (en) | 2008-12-29 |
MX2008008113A (en) | 2008-09-30 |
CN101336358A (en) | 2008-12-31 |
AU2006326947A1 (en) | 2007-06-28 |
KR101497297B1 (en) | 2015-03-02 |
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