WO2018107210A1

WO2018107210A1 - Compact cooling device

Info

Publication number: WO2018107210A1
Application number: PCT/AU2017/051342
Authority: WO
Inventors: Stephen David White; Roger Reece; Mark Peristy; Stuart Hands; Mark Jared GOLDSWORTHY; Ganapathi Subbu Sethuvenkatraman; Daniel David ROWE
Original assignee: Commonwealth Scientific And Industrial Research Organisation
Priority date: 2016-12-12
Filing date: 2017-12-06
Publication date: 2018-06-21
Also published as: AU2016273838B2; AU2016273838A1

Abstract

An indirect evaporative cooler comprising: (a) an air inlet for supplying primary air to the cooler; (b) a heat exchanger having a primary air side and a working air side; (c) a working air inlet zone for receiving working air, said inlet zone comprising: • a water particle dispersion air space in fluid communication with a working air side inlet of the heat exchanger; • a water particle generator for dispersing water particles into the water dispersion air space to form airborne water particles; • a low or non-pressurised working air for carrying the water particles from the water particle dispersion air space to the working air side inlet of the heat exchanger; (d) a fan for supplying working air to the water particle dispersion air space; and (e) a water particle collection surface for collecting airborne water particles, the water particle collection surface being in fluid communication with (i) said water particle dispersion air space and (ii) the working air side inlet of the heat exchanger.

Description

COMPACT COOLING DEVICE

[001 ] PRIORITY CROSS-REFERENCE The present application claims priority from Australian Patent Application No. 2016273838 filed on 12 December 2016, the contents of which are to be incorporated into this specification by this reference.

TECHNICAL FIELD

[002] The present invention is directed to a compact cooling device, systems and methods or use thereof and in particular to an indirect evaporative cooler for domestic use.

BACKGROUND TO THE INVENTION

[003] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[004] Evaporative cooling has long been used as a means of efficiently using the latent heat of vaporisation of water to reduce the air temperature and thus improve human comfort levels. However, as evaporative cooling results in an increase in humidity, human comfort levels have not always effectively improved. [005] Indirect evaporative cooling avoids the increase in humidity by containing the evaporation of water to one side (working air side) of a heat exchanger wall while a separate air flows over the opposing wall surface (primary air side), the heat exchanger wall enabling the transfer of heat but not the moisture. This configuration ensures the primary air stream is cooled, while maintaining the same humidity level, thus improving the overall comfort delivery. [006] While indirect evaporative coolers offer an energy efficient solution to cooling needs, its widespread adoption has been limited by its size, shape and weight which makes it difficult to blend into a domestic dwelling environment. Unfortunately use of simple directional water spray nozzles has struggled to evenly distribute water across the full heat exchanger entry plane leading to a bulky water distribution zone and/or reduced heat exchanger performance. In addition, the modest performance of indirect evaporative coolers on humid days has led to the market having a preference for refrigerative cooling devices. However, changing lifestyles and rising energy costs provides a market opportunity to revisit this technology in a form which addresses consumer needs.

[007] The present invention addresses the need for a more compact cooling device which can provide an energy efficient cooling solution.

SUMMARY OF THE INVENTION

[008] In a first aspect of the present invention, there is provided an indirect evaporative cooler comprising:

a) an air inlet for supplying primary air to the cooler;

b) a heat exchanger having a primary air side and a working air side;

c) a working air inlet zone for receiving working air, said inlet zone comprising:

• a water particle dispersion air space in fluid communication with a working air side inlet of the heat exchanger;

• a water particle generator for dispersing water particles into the water dispersion air space to form airborne water particles; • low or non-pressurised working air for carrying the water particles from the water particle dispersion air space to the working air side inlet of the heat exchanger;

d) a fan for supplying working air to the water particle dispersion air space; and e) a water particle collection surface for collecting airborne water particles, the water particle collection surface being in fluid communication with (i) said water particle dispersion air space and (ii) the working air side inlet of the heat exchanger.

[009] The water particle collection surface, for the purposes of the present invention, is a surface which promotes the settling or impingement of airborne water particles onto a surface in communication with the internal surfaces of the working air heat exchanger channels. The surface may also facilitate condensation of water vapour in saturated or super saturated working air. The water particle collection zone may form part or all of the heat exchanger (e.g. the manifold channel) and it may form part or all of a water particle collection surface separate from the heat exchanger, but in direct communication thereof.

[010] The cooler of the present invention utilises water particles as an efficient delivery mechanism for the formation and replenishment of a water film for coating the internal surfaces of the working air heat exchanger channels. The use of water particles has been traditionally used for humidification and, as such, it is unexpected that use of water particles specifically to generate a uniform water film would be so effective.

[01 1 ] In one embodiment, the water particle collection surface comprises a duct surface at an offset angle from a duct surface of the water particle dispersing air space. The offset angle is preferably between 30 and 120 degrees and more preferably about 90 degrees. The offset angle in the duct causes a change in air flow direction which promotes settling or impingement of the water particles on the water particle collection surface, thereby facilitating the creation of water droplets or a water film. To further promote water particle impingement onto the water particle collection surface the cooler may have an auxiliary fan positioned within the heat exchanger inlet zone for directing the airborne water particles against a surface of the water particle collection surface. Within this embodiment, the auxiliary fan preferable changes the direction of airflow such that the greater proportion of water particles are impinged against the surface of the water particle collection surface than would have without the use of the auxiliary fan.

[012] The water particles preferably have a size distribution such that the water particles are suspended in and travel along with the working air, i.e. the water particles travel in the working air at approximately the same speed and direction as the working air stream, such that the water particles goes wherever the air stream goes, thereby creating even distribution. This contrasts with a spray /jet atomiser where the water typically travels at a higher velocity and/or direction to the air stream flow to deliver a concentrated zone of water particles.

[013] The air stream travelling through the water particle dispersion air space preferably has a flowrate in the range of 10 to 1000 litres per second; more preferably 20 to 500 litres per second and more preferably in the range of 30 to 200 litres per second. The linear velocity of the air stream is preferably in the range of 1 to 40 metres per second and more preferably between 2 and 20 metres per second. The air stream is preferably in turbulent flow with a Reynold's number of preferably greater than 2000 and more preferably greater than 10,000.

[014] Preferably, the air stream travelling through the water particle dispersion air space travels a tortuous path prior entering the working air side inlet of the heat exchanger. The tortuous path preferably means that the direction of the airstream travelling through the water particle dispersion air space is at angle greater than 100° to the direction of the airstream entering the working air side inlet of the heat exchanger and preferably at an angle of greater than 150°. Preferably, the water particles flow through the working air side of the heat exchanger under the influence of gravity, i.e. the water particles flow downwards.

[015] Preferably, the water particle generator is an airless emitter, meaning that the water particle generator deposits water particles into the working air, without the water particle generator being a source of working air.

[016] Preferably, the water particle generator does not use pressurised air or water to generate and/or emit the water particles. In one embodiment, the water particle generator uses the low or non-pressurised working air to generate and/or emit the water particles.

[017] In one embodiment, the emission and generation of water particles is achieved through vibrational forces, such as in an ultrasonic water particle generator. Preferably, the water particle generators emit water particles having a particle size distribution with a D90 of less than 300 microns; more preferably less than 200 microns and even more preferably less than 150 microns. Water particles within this water size range are readily suspended in the air and carried from the water particle dispersing air space to the water particle collection surface. For the purposes of the present invention airborne water particles are water particles suspended in the air such that the particles may be distributed by the working air flow stream.

[018] In a preferred embodiment, the water particle generator is positioned below the working air stream prior to entry into the heat exchanger and more preferably on a relatively horizontal plane. The velocity of the water particles emitted from the water generator is preferably less than required for the water particles to impinge against an opposing surface, thereby allowing the water particles to become suspended within the working air stream.

[019] In one embodiment, the water particle generator is positioned at or below the heat exchanger working air inlet. Within this embodiment, prior to entering the heat exchanger, the emitted water particles preferably travel with the working air in a horizontal and/or upward direction.

[020] While any suitable water particle generator may be used. Preferably, the water particle generator utilises low pressure or non-pressured air. Preferably the water particle generators are ultrasonic particle generators. Ultrasonic particle generators provide a low energy input means of generating the water particles, thereby contributing to a high energy efficient cooler. In addition, the use of ultrasonic particle generates increases simplicity of the design and reduces maintenance compared to the use of conventional pumps in combination with spray bars or jet atomisers.

[021 ] The working air inlet zone preferably comprises a low pressure working air stream of preferably less than 25 psi (gauge or absolute), more preferably less than 20 psi (gauge or absolute) and even more preferably less than 16 psi (gauge or absolute). In one embodiment, the working air stream is non-pressurised. For the purposes of the present invention, non-pressured working air means working air which enters the water particle dispersion air space via the fan. (i.e. the air does not enter via a pressurised air nozzle or the like).

[022] In another embodiment, particularly suited to portable coolers, the working air inlet zone comprises a low pressure working air stream of preferably less than 1000 Pa gauge, more preferably less than 500 Pa gauge and even more preferably less than 300 Pa gauge. These low pressures enables the cooler to operate quietly and efficiently.

[023] The advantage of having a low pressure of non-pressurised air is that the water particles may travel along the substantive length of the heat exchanger depositing a portion of the water particles over its substantive length, thereby replenishing a thin film of water on in the internal surface of the heat exchanger. Using high pressure air, the water particles are more susceptible to travelling directly through the heat exchanger tube with no or minimal water deposited (i.e. no film) or, for more tortuous pathways, a large proportion of water particles impinge upon at a surface in or before the heat exchanger (i.e. thick film). In either scenario, heat transfer efficiency may be less than optimal.

[024] The generation of water particles in a mist or aerosol form generally promotes convective heat transfer, which is considered detrimental to the performance of an indirect evaporative cooler. However, the cooler of the present invention is able to collect at least a portion of the water particle laden air to generate a thin film on the internal surfaces of the heat exchanger channels. It has been found that the cooler of the present invention provides water particles which can both form a thin film of water for evaporation as well as continually replenish the water film through the water particles impinging or settling (inertia impaction) upon the surface (or water thin positioned thereon) of the working air side of the heat exchanger. The impinging or settling of the water particles preferably occurs along the substantial length of the working air side of the heat exchanger. Preferably at least 10%, more preferably at least 20%, even more preferably at least 40% and yet even more preferably at least 60% of the total length of the working air side of the heat exchanger is replenished by the impingement or settling of water particles from the adjacent working air stream.

[025] The further the water particles settle or impinge upon the heat exchanger channel the more consistent the water film on the channel is likely to be and the better the heat exchanger performance as a result. In addition, the further along the heat exchanger channel that the water particles travel within the working air, the greater the amount of evaporation of water particles is generated, thereby contributing the cooling effect from the working air side of the heat exchanger. This operation contrasts to the conventional operation of an indirect evaporative cooler heat exchanger in which the working air channel is cover by a water film, but there is an absence of water particles suspended in the stream air above (Figure 1 a).

[026] Due to the use of airborne water particles to create and replenish the evaporative thin film covering the working air side of the heat exchanger, the contribution of convective heat transfer to the total heat transfer in the heat exchanger is greater than typical heat exchangers within indirect evaporative coolers.

[027] The use of the auxiliary fan is preferably combined with an ultrasonic water particle generator. The net energy input of this water film forming mechanism is inherently better than achieved using jet atomisers directed against a surface, which relies on high pressure to generate high velocity water particles.

[028] In another embodiment, the water particle collection surface comprises a duct of larger diameter than the duct defining the water particle dispersing air space. The increase in cross sectional area results in a reduced air velocity.

[029] The change in velocity or direction of the suspended particles favours the impingement of the larger particles in the working air stream, thereby favouring the smaller water particles to continue further along the heat exchanger channels to thereby replenish the water film covering the working air heat exchanger channels. Through controlling the water particle size distribution, the proportion and location of water particle impingement within the entrance and in the heat exchanger may be controlled.

[030] In one embodiment, the water particle dispersion air space is separate from the heat exchanger. The water particle generator is preferably offset horizontally from the inlet of the heat exchanger. Preferably, the water particle generator emits air into a water particle dispersion air space which is offset from the entrance to the heat exchanger such that water particles flow a non-linear path to enter the heat exchanger. The non-linear path may involve the working air stream changing direction of at least 20 degrees and more preferably at least 60 degrees from the direction of the emitted water particles from the water generator. This configuration of working air inlet zone requires at least a portion of the water particles to flow into the heat exchangers along with the working air, as opposed to the water being sprayed directly into the heat exchangers.

[031 ] In a further embodiment, the water particle dispersing air space comprises baffles, variations in duct diameters and/or directions to thereby promote mixing of the water particles and the working air stream.

[032] In a preferred embodiment, the cooler comprises a single fan for both feeding the indirect evaporative heat exchanger and for delivering the product air (i.e. primary air ex-heat exchanger). This is preferably achieved through the fan transferring the inlet air through the heat exchanger after which a portion of the air is diverted to the working air side of the heat exchanger and a portion is diverted to the product air outlet. The use of a single fan is possible through balancing the pressure drop across the two air flow pathways.

[033] The collected water preferably flows from the surface of the water particle collection surface into the internal surfaces of the heat exchanger channels under the force of gravity. Alternatively, or in addition to, the water particle collection surface may direct the collected water into a water reservoir which is preferably used as a source of water for the water particle generator.

[034] Preferably, the settling of water vapour and particles on the surface of the water particle collection surface is further advanced through the use of a hydrophilic surface. The surface preferably has an apparent contact angle of the surface with water, is preferably less than 50° degrees at time = 10 seconds (after wetting), and more preferably is less than 20° degrees after 10 seconds (after wetting).

[035] In a preferred embodiment, the hydrophilic surface comprises a plurality of wicks. The wicks preferably form the entrance to the heat exchanger channels, providing a high surface a low free energy surface to capture a significant portion of water from the air stream.

[036] While indirect evaporative coolers are able to reduce the ambient air temperature without increasing humidity, in low humidity environments the effectiveness of the cooler may be enhanced through the use of a direct evaporative cooling, either alone or in combination with indirect evaporative cooling. Within this embodiment, a duct defining the water particle dispersing air space further comprises a closable aperture for depositing water particles into a product air channel adjacent to the water particle dispersing air space, said product air channel distinct from water particle dispersing air space. [037] When operating in a direct evaporative cooling mode, the water particles from the water particle generator are preferably transferred from the water particle dispersing air space to the product air channel through use of a venturi effect. This may be achieved when the initial ratio of the cross section area of the product air channel and the duct connecting to the water particle dispersing air space after the splitting point being higher than the ratio at the point where the product air channel and the water particle dispersing air space are connected via the closable aperture. Under this configuration, the air flowing through the product air channel is of a higher velocity than the working air flow in the adjacent water particle dispersing air space. Therefore, when the aperture between the product air and the working air is opened a venturi effect is created, drawing water particles from the water particle air space through to the product air channel and out the outlet vent.

[038] The closable aperture may be manually or electronically actuated to change the cross sectional area of the opening between the two zones. There may be a single or a plurality of closable apertures. In one embodiment, the cooler further comprises a heat exchanger inlet shutoff mechanism for preventing the inlet air from entering the heat exchange channels and instead diverting the inlet air into the product air channels when used in co-operation with the closable aperture(s), with the shutoff mechanism preferably positioned downstream of the water particle dispersing air space. Within this mode, the cooler operates as a direct evaporative cooler or humidifier.

[039] In a second aspect of the present invention, there is provided a heat exchanger, suitable for use in the first aspect of the present invention, which comprises a plurality of primary air side channels and working air side channels each of the channels comprising an inlet and an outlet, wherein the working side channels comprises a water collection surface proximal to the working air inlet, said water collection surface comprising a manifold channel in fluid communication with a core section, said core section comprising a plurality of channels with one or more of the plurality of channels being distal to the working air inlet and/or outlet.

[040] In one embodiment, the said water collection surface comprises the manifold channel. In another embodiment, the water collection surface consists of the manifold channel.

[041 ] The volume to surface area ratio of the manifold channel is preferably greater than the volume to surface area ratio of the core section. The increased ratio promotes working air and water particle mixing prior to entry to the mixture into the core zone. Preferably, the surface area to volume ratio in the manifold channel is at least 50%, more preferably at least 100% and even more preferably at least 200% greater than the surface area to volume ratio in the core section.

[042] While a portion of the suspended water particles will impinge or settle upon the manifold channel's water collection surface, the relatively higher working air volume to the manifold's surface area, compared to the core section, contributes to a greater proportion of heat absorption being attributable to evaporation of the suspended water particles relative to evaporation on water on the manifold wall.

[043] Consequently, the Nusselt number (representing the relative proportion of convective to conductive heat transfer) of the manifold channel(Nu_m) is preferably greater than the Nusselt number of the core section (Nu_c). Preferably Nu_m is at least 10%, more preferably at last 20% and even more preferably at least 50% more than Nuc

[044] The diameter of the channels (taken from the widest point) in the core section is preferably between 2mm and 20mm, more preferably between 2.5mm and 10mm; even more preferably between 3mm and 8mm; and yet even more preferably between 3.5mm and 7mm. The preferred diameter may dependent upon the contact angle between the water particle and the channel surface and the size of the water particle.

[045] Preferably the ratio between a working air side channel diameter in the core section to the D₉₀ water particles emitted by the water particle generator is at least 5, more preferable at least 10, even more preferable at least 20, yet even more preferably at least 30; and most preferably at least 50. Preferably the ratio between the working air side channel diameter to the Dgo water particles is no more than 150 ; even more preferably no more than 100 and yet even more preferably no more than 50.

[046] If the working air side channel diameter is too small, then water particle impingement may result in the channels filling up with water, thus inhibiting thin film formation and the evaporation thereof. Larger diameters may result in lower water particle impingement rates and/or less than optimal ratios of working air volume to the surface area of the thin film.

[047] The primary air side and working air side channels are preferably configured in a cross current and/or counter current flow configuration. Preferable the primary air side and working air side channels are configured in a cross current and a counter current arrangement. This arrangement is possible due to the use of the manifold channel, preferably on the working air side, which enables the working air to be diverted from a cross flow configuration to a counter flow configuration.

[048] The direction of air flow from the heat exchanger working air inlet is preferably offset from the direction of air flow in core section. The change or direction in airflow facilitates mixing of water particles within the manifold channel and also may promote impingement of water particles against the manifold surface.

[049] Preferably, the water collection surface interfaces with the core section such that the inlet opening of each channel in the core section has an bottom surface component interfacing and exposed to the water collection surface, such that water particles settling or impinging on a channel opening flow into the channel or a water film flowing down a surface of the water collection surface diverts water into the inlet opening of each channel in the core section. Such an arrangement promotes a uniform water distribution between each of the channels in the core section.

[050] In a third aspect of the present invention there is provided a use of the cooling device of the first aspect of the present invention for the cooling of an air space. The air space is preferably an enclosed air space, such as an enclosed room. Preferably, the cooling device is used to cool a portion of the enclosed room, preferably no more than 20m³. This is be achieved through directing the product air stream to a localised portion of the enclosed space, such as where a person or persons are sitting, standing, reclining or sleeping. For the purposes of the present invention, a heat exchanger means a surface or surfaces which heat is transferred between the working air and the primary air.

[051 ] For clarity, reference to a ratio of X, is reference to a ratio of X: 1 (e.g. 5: 1 ) [052] The terms working air and working air side may be used interchangeably, where appropriate.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[053] The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein: [054] Figure 1 illustrates the operation of a conventional indirect evaporative cooler (a) working principle of the indirect evaporative cooler, (b) configuration of a cross flow IEC heat exchanger; and (c) a psychrometric illustration of the air treatment process in the IEC heat exchanger.

[055] Figure 2 is a schematic diagram of a conventional IEC.

[056] Figure 3a is a schematic diagram of a cooler within one embodiment of the present invention.

[057] Figure 3b is a schematic diagram of a cooler within another embodiment of the present invention.

[058] Figure 3c is a schematic diagram of a cooler within a further embodiment of the present invention.

[059] Figure 4 is a schematic diagram of a water collection and water particle collection surfaces of a cooler of the present invention.

[060] Figure 5 is a schematic diagram of an isometric view of a heat exchanger within one embodiment of the present invention.

[061 ] Figure 6 is a schematic diagram of a top view of the heat exchanger of Figure 5.

[062] Figure 7 is a schematic diagram of a side view of the heater exchanger of Figure 5.

[063] Figure 8 is a schematic diagram illustrates variations in the heat exchanger configuration in respect to primary air and working air inlet and outlet.

DETAILED DESCRIPTION

[064] It should be understood that various directions such as "upper", "lower", "bottom", "top", "left", "right", and so forth are made only with respect to explanation in conjunction with the drawings, and that the components may be oriented differently, for instance, during transportation and manufacturing as well as operation. Because many varying and different embodiments may be made within the scope of the inventive concept(s) herein taught, and because many modifications may be made in the embodiments described herein, it is to be understood that the details herein are to be interpreted as illustrative and non-limiting.

[065] The principles of indirect evaporative coolers are represented in Figure 1 which presents the working principle and psychometric illustration of the air treatment process relating to an indirect evaporative cooling operation. During operation, the primary (product) air enters into the dry channel while the secondary (working) air enters into the adjacent wet channel. The primary air is cooled by the sensible heat transfer between the primary air and the plate, which is induced by the latent heat transfer relating to water evaporation from the plate's wet surface to secondary air. As a result, the primary air (state 1 ) is cooled at the constant moisture content and moves towards the wet-bulb temperature of the inlet secondary air; whereas the secondary air of state 1 is gradually saturated and changed into state 2' at its earlier flow path, then heated when moving along the flow path and finally discharged to atmosphere in the saturated state 3. It should be noted that to enable heat transfer between the dry side air to wet side air, the state 3 should have a lower temperature than the state 2 and theoretically speaking, the enthalpy decrease of the air within the dry side channel is equal to the enthalpy increase of the air within the wet side channel ,i.e., h1 -h2=h3-h1 .

[066] Figure 2 illustrates a conventional indirect evaporative cooler which comprises a water spray distribution system to generate a falling film of water to coat the secondary air side of the heat exchanger. [067] A preferred embodiment of the invention is illustrated in Figure 3a of an indirect evaporative cooling comprising an air inlet 5 which transfers primary air through the primary air side of a heat exchanger 50 to the heat exchanger working air inlet zone 10 via the action of the fan 35. The working air then enters the water particle dispersing air space 15 in which a water particle generator 20 emits water particles therein. The water laden working air then travels to a water particle collection surface 25 when water vapour and/or fine airborne water particles settles/condenses onto surfaces forming the water particle collection surface. In some embodiments the water particle collection surface may extend into the working air side of the heat exchanger channels 27, as further detailed in reference to Figure 5.

[068] The collected water flows into the heat exchanger channels 30 forming a thin film on the internal surfaces. As the thin film travels down the heat exchanger channels, the heat from the primary air side of the heat exchanger tubes transfer heat to the thin water film on the working air side, thereby reducing the temperature of the primary air which is delivered as a cool air stream out the vent of the cooler 40. The transferred absorbed heat results in evaporation of the thin film with the humid air exiting the heat exchanger 45.

[069] The cooler is preferable only reliant on a single fan 35 to deliver the primary air to both the outlet vent 40 and the heat exchanger working air inlet zone 10, with part of the cooled primary air (exiting the heat exchanger being diverted to the working air side of the heat exchanger 10.

[070] Figure 3b illustrates an alternative embodiment of the cooler of the present invention. Within this embodiment, the primary air inlet 5 and the working air outlet 45 are on the same side of the cooler to enable the primary air outlet duct and the working air outlet duct to be connected along a substantial portion of their length (not shown). In contrast to Figure 3a, the single fan 35 is orientated on a horizontal axis and is positioned beside the lower half of the heat exchanger 10. The pump 32 supplies water from a first reservoir 34 to a second reservoir 36 which supplies an ultrasonic atomiser 20. The pump works intermittently to fill the second reservoir, with a level sensor 42 on the second reservoir activating the pump to switch on when water levels drop to a designated level. The level sensor of the first reservoir 44 sends a signal to the control panel 46 when it requires to be manually replenished.

[071 ] The primary air flow through the primary air side of the heat exchanger 10 after which a portion of the primary air is diverted to the working air side of the heat exchanger where the air stream passes through a water distribution zone 52 and then the air stream is redirected 180 degrees through a manifold channel 54 within the heat exchanger. The manifold channel is triangular in shape with the cross- sectional area of the inlet diminishing as the working air progressively is diverted into the core section of heat exchanger channels 56. The cross-sectional area of the duct 52 immediately prior to the heat exchanger inlet is lower than the cross- sectional area of the manifold channel 54, thereby slowing the water particles down as they change direction and enter the manifold channel. This reduces the relative amount of water particle impingement in the manifold channel to enable sufficient quantity of water particles to settle and replenish the water film on the heat exchanger channels further away from the heat exchanger entrance (e.g. core section). For Figures 3b and 3c, the manifold channel 54 and the heat exchanger channels 56 function as a water particle collection surface 25. A manifold section 57 may also be placed at the outlet of the core section of the heat exchanger 10 for changing the direction of flow of the working air outlet from counter flow to cross sectional flow

[072] Figure 3c illustrates a further embodiment of a cooler of the present invention. As with the cooler of Figure 3a, the fan; the main/first reservoir; and the pump are all located below the heat exchanger to reduce the height of the centre of gravity. Figure 3c also illustrates a primary air (product air) outlet vent. The vent is preferably adjustable such the pressure drop over the outlet section can be adjusted, so as to balance the relative pressure drop from product air outlet and the working air side of the heat exchanger at the splitting point 62 which may be required when running the cooler in a single fan configuration.

[073] The coolers of Figures 3a and 3b have a water particle generator positioned below the heat exchanger inlet, such that the water particles are required to travel upwards with the working air. Any impingement or condensation of water particles on the side ducts results in the water falling back down into the second water reservoir 36. Within this configuration, a greater proportion of the water particles entering the heat exchanger are suspended in air, rather than forming a thin water film of the surface of the heat exchanger. As illustrated in Figure 4, the primary air 60 is diverted into a working air stream 65 and a product air stream 70 at the splitting point 105. The working air stream passes through the water particle dispersing air space 75 thereby mixing and dispersing a plurality of water particles 1 10 (not shown to scale). The trajectory of the air flow is changed through the duct work making a greater than 90 degree turn 80. The increased density of the water particles promotes a portion of the airborne particles to settle or impinge upon the water particle collection surface 80 and from a thin film which flows down into the heat exchanger channels 85. Condensation or settling of water (inertia impaction) may also occur on hydrophilic wicks 90 disposed on the opening of the heat exchanger channels. A portion of the airborne particles travels within the heat exchanger channels settling upon the wetted surfaces to thereby replenish the wetted surface areas to ensure a consistent coverage of water is presence of the channel surfaces. The exhausted working air stream 95 while being of increased humidity compared to the inlet air 60, is preferably substantially free of airborne water particles.

[074] The product air stream 70 preferably narrows relative to the working air stream 65, such that a venturi effect is able to draw water particles from the water particle dispersing air space 75 through the closable aperture 100 and into the product air stream. The water particles are preferable dissipated through the outlet vent with the fine water particles further absorbing heat from the surrounding atmosphere. The narrowing of the product air stream relative to the working air stream also assists in the balancing of pressure drop across the two different flow paths and thereby enables a single fan drive air flow across the two flow pathways. With reference to Figure 5 to 7, there is provided a heat exchanger 200 for an indirect evaporative cooler of the present invention. The heat exchanger comprises a plurality of working air (secondary air) channels 210 and a plurality of primary air channels 220. The exchanger has a working air inlet 230 preferably position at the top portion of the heat exchanger. The working air outlet 240 is preferably positioned at the bottom portion of the heat exchanger.

[075] The primary air inlet 250 and outlet 260 are preferably connected by a plurality of parallel channels.

[076] The working air inlet may connect to a manifold channel 270, which forms part or all of the water collection surface. As indicated in top and side view perspectives in Figure 6 and 7, there may be a plurality of manifold channels forming the water collection surface. The manifold channel preferably has a tapered configuration with a larger cross sectional area proximal to the inlet 270, than distal to the inlet 280.

[077] A water distribution (not shown) device adds water as airborne particles and/or a thin film which flows under gravitational forces down the surfaces of the manifold channel 270.

[078] The direction of air flow from the inlet and/or outlet is preferably offset from the direction of air flow in core section 290. This change in air flow conditions promotes settling or impingement of the airborne water particles on the surface of the manifold channel. This arrangement also facilitates the ability of the cooler to use a single fan to draw in primary air and recirculate a portion of the primary air output (supply air) to the working air side of the heat exchanger 230. The wider diameter of the manifold channels in comparison to the plurality of channels on the primary air side of the heat exchanger facilitates the balancing of the pressure drop over the primary and working air sides of the heat exchanger, with the wider channels helping to compensate for the pressure drops due to the air flow directional changes in on the working air side of the heat exchanger.

[079] The tapered configuration of the manifold channel has the combined benefits of assisting water film formation as well as reducing the pressure drop over the manifold section relative to conventional manifold configurations.

[080] The manifold section 270 interfaces with the core section 290 such that the inlet opening of each channel in the core section has an bottom surface component interfacing and exposed to the manifold channel above, such that water particles settling or impinging on the opening flow into each channel or a water film flowing down a surface of the manifold channel would divert water into the inlet opening of each channel. To facilitate the flow of water along the surfaces in the secondary channels, the channels are preferably downwardly inclined, preferably between 0 and 90 degrees from a horizontal plane.

[081 ] Within the core section of the secondary air channels, the secondary air and the primary air channels are configured in counter current flow. Within the manifold section, the working air side of the heat exchanger operates in a cross flow configuration to the primary air side flow, with the cross flow configuration transforming to a counter current configuration as the working air entering the inlet of the core section.

[082] The construction of the heat exchanger may be achieved from a plurality of sheets supported by interconnecting ribs supports. In particular, a channel may be formed from an upper sheet and a lower sheet and a plurality of rib supports interconnecting said upper and lower planar sheets.

[083] The sheets and/or ribs supports are manufactured from a plastic material, such as polypropylene. In one embodiment commercial available fluted plastic board, such as Corflute™ may be used to construct the heat exchanger panels. When using commercially available fluted plastic board, the manifold section may be formed by cutting away segments of the ribbed support structures between the upper and lower sheets to thereby increase the cross-sectional area of the channel.

[084] Figure 8 provides examples of variations in the heat exchanger flow configurations which may be used under one or more aspects of the present invention.

[085] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention. [086] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.

Claims

CLAIMS:

1 . An indirect evaporative cooler comprising:

(a) an air inlet for supplying primary air to the cooler;

(b) a heat exchanger having a primary air side and a working air side;

(c) a working air inlet zone for receiving working air, said inlet zone comprising:

• a water particle generator for dispersing water particles into the water dispersion air space to form airborne water particles;

• a low or non-pressurised working air for carrying the water particles from the water particle dispersion air space to the working air side inlet of the heat exchanger;

(d) a fan for supplying working air to the water particle dispersion air space; and

(e) a water particle collection surface for collecting airborne water particles, the water particle collection surface being in fluid communication with (i) said water particle dispersion air space and (ii) the working air side inlet of the heat exchanger.

2. The cooler according to claim 1 , wherein the water particle generator utilises the low or non-pressured working air for generating and/or emitting the water particles.

3. The cooler according to claims 1 or 2, wherein the water particle generator emits water particles having a particle size distribution with a D90 of less than 300 microns.

4. The cooler according to claim 2, wherein the water particle generator emits water particles having a particle size distribution with a D90 of less than 200 microns.

5. The cooler according to any one of the preceding claims, wherein the water particle generator is positioned at or below the heat exchanger working air side inlet.

6. The cooler according to any one of the preceding claims, wherein the water particle generator is an ultrasonic particle generator.

7. The cooler according to any one of the preceding claims, wherein the water collection surface comprises a duct surface at an offset angle from a duct surface adjacent the water particle dispersion air space.

8. The cooler according to claim 7, wherein the offset angle between the water collection surface and the duct surface adjacent the water particle dispersion space is in the range of 30 to 120 degrees.

9. The cooler according to any one of the preceding claims, wherein the water particle collection surface comprises a duct having a diameter larger than the duct diameter defining the water particle dispersion air space.

10. The cooler according to any one of the claims, wherein the water particle collection surface comprises the entrance to the plurality of heat exchanger channels.

1 1 . The cooler according to any one of the preceding claims, wherein the water particle collection surface is hydrophilic.

12. The cooler according to claim 1 1 , wherein the hydrophilic surface comprises a plurality of wicks.

13. The cooler according to any one of the preceding claims, wherein a duct defining the water dispersing air space further comprises a closable aperture for depositing water particles into a product air channel adjacent to the water particle dispersing air space, said product air channel distinct from water dispersing air space.

14. The cooler according to claim 13, wherein the fan supplies inlet air to both the water particle dispersing air space and the product air channel, said primary air divides into the product air channel and the water particle dispersing air space at a splitting point.

15. The cooler according to claim 13 or 14, wherein the initial ratio of the cross section area of the product air channel and a working air channel at the splitting point duct is higher than the cross sectional ratio at the point where the product air channel and the water particle dispersing air space are connected via the closable aperture, such that water particles flow through the closable aperture into the product air channel.

16. The cooling according to any one of the preceding claims, wherein a single fan is used to convey the primary and the working air through the heat exchanger.

17. The cooler according to any one of the preceding claims, wherein the water particle generator emits water particles into a water particle dispersion air space which is offset from the entrance to the heat exchanger such that water particles flow in a non-linear path to enter the heat exchanger.

18. A heat exchanger for use in the cooler according to any one of the preceding claims, wherein the heat exchanger comprises a plurality of primary air side channels and working air side channels each of the channels comprising an inlet and an outlet, wherein the working side channels comprises a water collection surface proximal to the working air inlet, said water collection surface comprising a manifold channel in fluid communication with a core section, said core section comprising a plurality of channels with one or more of the plurality of channels being distal to the working air inlet and/or outlet.

19. The heat exchanger according to claim 18, wherein the volume to surface area ratio of the manifold channel is greater than the volume to surface area ratio of the core section.

20. The heat exchanger according to claims 18 and 19, when in operation, has a Nusselt number of the manifold channel (Nu_m) greater than the Nusselt number of the core section.

21 . The heat exchanger according to any one of claims 18 to 20, wherein the ratio between a working air side channel diameter within the core section to the D₉₀ water particles emitted by the water particle generator is at least 5 and no more than 200.

22. The heat exchanger according to any one of claims 18 to 21 , wherein the ratio between a working air side channel diameter within the core section to the D₉₀ water particles emitted by the water particle generator is at least 10 and no more than 50.

23. The heat exchanger according to any one of claims 18 to 22, wherein the direction of air flow from the working air heat exchanger inlet is offset from the direction of air flow in core section.

24. The heat exchanger according to any one of claims 18 to 23, wherein the working air channels and the primary air channels are configured in a cross flow and counter flow arrangement.

25. The heat exchanger according to any one of the preceding claims, wherein the water collection surface interfaces with the core section such that the inlet opening of each channel in the core section has an bottom surface component interfacing and exposed to the water collection surface, such that water particles settling or impinging on a channel opening flow into the channel or a water film flowing down a surface of the water collection surface diverts water into the inlet opening of each channel in the core section.

26. The cooler according to claim 1 to 17, comprising a heat exchanger according to any one of claims 18 to 25.

27. Use of a cooling device of any one of claims 1 to 17 and 26 for cooling an air space.

28. Use according to claim 27, wherein the air space is a portion of an enclosed space.

29. Use according to claim 28, wherein the volume of the portion of the enclosed space is no more than 20 m³