AU2016273838B2

AU2016273838B2 - Compact cooling device

Info

Publication number: AU2016273838B2
Application number: AU2016273838A
Authority: AU
Inventors: Mark Jared GOLDSWORTHY; Stuart Hands; Mark Peristy; Roger Reece; Daniel David Rowe; Ganapathi Subbu Sethuvenkatraman; Steven David White
Original assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Current assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date: 2016-12-12
Filing date: 2016-12-12
Publication date: 2023-06-01
Anticipated expiration: 2036-12-12
Also published as: WO2018107210A1; 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. FIGURE 2 -2/9 `-Exha usIt a ir sprayss Supply air Hetechanger Peednary aar 83,eto n d ay air Pump "\ Vk~estaliass steel sump Figure 2

Description

-2/9

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COMPACT COOLING DEVICE TECHNICAL FIELD

[001] 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

[002] 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.

[003] 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.

[004] 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.

[005] 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.

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

SUMMARY OF THE INVENTION

[007] In a first aspect of the present invention, there is provided an indirect evaporative cooler comprising: (a) an air inlet that supplies 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 that receives 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; and (d) a fan that supplies working air to the water particle dispersion air space; and wherein the working air inlet zone comprises: a water particle generator that disperses water particles into the water dispersion air space to form airborne water particles; and a low pressure or non-pressurised working air stream of less than 25 psi that carries the water particles from the water particle dispersion air space to the working air side inlet of the heat exchanger; and wherein the indirect evaporative cooler comprises: (e) a water particle collection surface that collects 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, wherein the collected airborne water particles form and replenish a water film coating surfaces of the working air side of heat exchanger, and wherein the heat exchanger transfers heat between the working air and the primary air.

[008] 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.

[009] 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.

[010] 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.

[011] 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.

[012] 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.

[013] 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 1000

to the direction of the airstream entering the working air side inlet of the heat

exchanger and preferably at an angle of greater than 1500. 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.

[014] 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.

[015] 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.

[016] 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.

[017] 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.

[018] 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.

[019] 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.

[020] 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

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).

[021] 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.

[022] 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.

[023] 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

% 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.

[024] 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 1a).

[025] 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.

[026] 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.

[027] 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.

[028] 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.

[029] 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.

[030] 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.

[031] 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.

[032] 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.

[033] 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 500 degrees at time = 10 seconds (after wetting), and

more preferably is less than 200degrees after 10 seconds (after wetting).

[034] 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.

[035] 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.

[036] 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.

[037] 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.

[038] 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.

[039] In one embodiment, the said water collection surface comprises the manifold

channel. In another embodiment, the water collection surface consists of the

manifold channel.

[040] 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.

[041] 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.

[042] Consequently, the Nusselt number (representing the relative proportion of

convective to conductive heat transfer) of the manifold channel(Num) is preferably

greater than the Nusselt number of the core section (Nuc). Preferably Num is at least

%, more preferably at last 20% and even more preferably at least 50% more than

Nuc.

[043] 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.

[044] Preferably the ratio between a working air side channel diameter in the core

section to the D 9 0 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 D 9 0 water particles is no more than 150 ;

even more preferably no more than 100 and yet even more preferably no more than

50.

[045] 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.

[046] 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.

[047] 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.

[048] 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.

[049] 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.

[050] For clarity, reference to a ratio of X, is reference to a ratio of X:1 (e.g. 5:1)

[051] The terms working air and working air side may be used interchangeably,

where appropriate.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[052] 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:

[053] 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.

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

[055] Figure 3a is a schematic diagram of a cooler within one embodiment of the

present invention.

[056] Figure 3b is a schematic diagram of a cooler within another embodiment of

the present invention.

[057] Figure 3c is a schematic diagram of a cooler within a further embodiment of

the present invention.

[058] Figure 4 is a schematic diagram of a water collection and water particle

collection surfaces of a cooler of the present invention.

[059] Figure 5 is a schematic diagram of an isometric view of a heat exchanger

within one embodiment of the present invention.

[060] Figure 6 is a schematic diagram of a top view of the heat exchanger of Figure

5.

[061] Figure 7 is a schematic diagram of a side view of the heater exchanger of

Figure 5.

[062] 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

[063] 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.

[064] 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., h-h2=h3-hl.

[065] 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.

[066] 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.

[067] 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.

[068] 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.

[069] 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

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.

[070] 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

[071] 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.

[072] 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

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 110 (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.

[073] 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.

[074] The primary air inlet 250 and outlet 260 are preferably connected by a

plurality of parallel channels.

[075] 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.

[076] 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.

[077] 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.

[078] 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.

[079] 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.

[080] 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.

[081] 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.

[082] 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 TM 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.

[083] 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.

[084] 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.

[085] 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

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. An indirect evaporative cooler comprising: (a) an air inlet that supplies 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 that receives 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; and (d) a fan that supplies working air to the water particle dispersion air space; and wherein the working air inlet zone comprises: • a water particle generator that disperses water particles into the water dispersion air space to form airborne water particles; and • a low pressure or non-pressurised working air stream of less than 25 psi that carries the water particles from the water particle dispersion air space to the working air side inlet of the heat exchanger; and wherein the indirect evaporative cooler comprises: (e) a water particle collection surface that collects 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, wherein the collected airborne water particles form and replenish a water film coating surfaces of the working air side of heat exchanger, and wherein the heat exchanger transfers heat between the working air and the primary air.
2. The cooler according to claim 1, wherein the water particle generator utilises the low pressure or non-pressured working air for generating and/or emitting the water particles.
3. The cooler as claimed in 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 as claimed in 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 as claimed in 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 as claimed in any one of the preceding claims, wherein the water particle generator is an ultrasonic particle generator.
7. The cooler as claimed in 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 as claimed in 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 as claimed in 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 as claimed in any one of the preceding claims, wherein the water particle collection surface comprises the entrance to the plurality of heat exchanger channels.
11. The cooler as claimed in any one of the preceding claims, wherein the water particle collection surface is hydrophilic, and preferably comprises a plurality of wicks.
12. The cooler as claimed in 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.
13. The cooler as claimed in claim 12, 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.
14. The cooler as claimed in claim 12 or 13, 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.
15. The cooler as claimed in 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 working air side inlet to the heat exchanger such that water particles flow in a non-linear path to enter the heat exchanger.
16. The cooler as claimed in any one of the preceding claims, comprising a heat exchanger that 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 air 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.
17. The cooler as claimed in claim 16, wherein the volume to surface area ratio of the manifold channel is greater than the volume to surface area ratio of the core section.
18. The cooler as claimed in claims 16 or 17, when in operation, has a Nusselt number of the manifold channel (Num) greater than the Nusselt number of the core section.
19. The cooler as claimed in any one of claims 16 to 18, wherein the ratio between a working air side channel diameter within the core section to the Do water particles emitted by the water particle generator is at least 5 and no more than 200.
20. The cooler as claimed in any one of claims 16 to 19, wherein the direction of air flow from the working air heat exchanger inlet is offset from the direction of air flow in core section.