WO2011126450A1

WO2011126450A1 - Method, system and device for heat exchange

Info

Publication number: WO2011126450A1
Application number: PCT/SE2011/050419
Authority: WO
Inventors: Eva Gudmundsson
Original assignee: Rototemp Ab
Priority date: 2010-04-09
Filing date: 2011-04-07
Publication date: 2011-10-13

Abstract

A dynamic heat exchanger for evaporative cooling is provided. The dynamic heat exchanger is adapted for heat exchange between a first humid gas (F₁) and a second gas (F₂) being less humid. The dynamic heat exchanger comprises a first and second cavity (3a, 4a) separated from each other. The first cavity (3a) is adapted to house a first humid gas (F₁), and the second cavity (4a) is adapted to house a second gas (F₂) being less humid. The first cavity (3a) is partially enclosed by a dynamic evaporation surface (12) adapted to evaporate a liquid that comes in to contact with the dynamic evaporation surface (12). The dynamic evaporation surface (12) is adapted to rotate such that particles on the dynamic evaporation surface (12) are removed by means of centrifugal force.

Description

METHOD, SYSTEM AND DEVICE FOR HEAT EXCHANGE Technical field

The present invention relates generally to a method and apparatus for dynamic heat exchangers for evaporative cooling.

Background art

[0001 ] Conventional heat exchangers are used to transfer heat from one flowing media to another flowing media. Heat exchangers have the drawback that heat exchange can only be obtained where the temperature of one media can be changed at most to the entering temperature of the second media. However, cooling of one media to a temperature below the second media cannot be obtained by recuperative or regenerative heat exchangers.

[0002] Cooling can be obtained by humidification of air. This is currently used for ventilation air that is introduced into buildings such as office buildings, homes, and animal stables. This method has the disadvantage that humidification is associated with health hazards for humans as well as animals, and that buildings can be damaged by the humid air.

[0003] Indirect evaporative cooling can be used to avoid the drawbacks of humidification. Thus, air to be cooled is passed through a heat exchanger. A second flow of air is humidified and thereby cooled and is allowed to pass through the heat exchanger in a space that is separated from the ventilation air. The ventilation air is thereby cooled. The moistened air can be carried away where it does not cause damage and where it does not cause health hazards.

[0004] Heat exchangers for indirect evaporative cooling has the large drawback that growth of microorganisms such as fungi, algae and bacteria can occur in the canals of the heat exchangers that carry humidified air. Besides generating potential health hazards, the growth of unwanted microorganisms will impede the heat transfer efficiency of the heat exchanger. The growth of microorganisms can even occur to such an extent that channels of the heat exchanger are clogged entirely. In addition, airborne dust may also clog the heat exchanger. According to standard practice in Germany, the distance between heat exchanging surfaces in a heat exchanger should not be less than 3 mm in order to prevent the risk for clogging by dust. However, in order to achieve an efficient heat transfer, it is desirable that the distance should be as small as possible. Thus, having a long distance between the surfaces in order to prevent clogging lessens the efficiency of the heat exchange. The above heat transfer efficiency problems and clogging problems are large disadvantages of indirect evaporative cooling, and heat exchangers employing this method are not much used as they require systems for killing and/or removing microorganisms. In addition, if the channels have to be large enough to prevent clogging by airborne dust, that too will greatly decrease the efficiency of the system.

[0005] EP058402 discloses a heat exchanger for dry air, where heat exchange takes place between streaming gases via heat transfer between the surfaces of rotating discs.

Summary of invention

[0006] A dynamic heat exchanger for evaporative cooling is provided. The dynamic heat exchanger is adapted for heat exchange between a first humid gas and a second gas being less humid. The dynamic heat exchanger comprises a first and second cavity separated from each other. The first cavity is adapted to house a first humid gas, and the second cavity is adapted to house a second gas being less humid. The first cavity is partially enclosed by a dynamic evaporation surface adapted to evaporate a liquid that comes in contact with the dynamic evaporation surface. The dynamic evaporation surface is adapted to rotate such that particles on the dynamic evaporation surface are removed by means of centrifugal force. By rotating the dynamic evaporation surfaces, centrifugal forces works to a larger extent on the particles than on the gases, thus pushing the particles radially outwards keeping the surfaces clean such that the gas can flow freely. By keeping the surfaces clean, the heat transfer efficiency and the efficiency of the heat exchanger is maintained.

[0007] According to one embodiment the dynamic heat exchanger further comprises at least one liquid spraying member adapted to spray liquid into a gas flow entering the dynamic heat exchanger, such that the gas is cooled when entering the dynamic heat exchanger.

[0008] According to another embodiment the dynamic heat exchanger comprises at least one liquid spraying member adapted to spray the liquid to be evaporated onto the dynamic evaporation surface, which reduces the friction that occurs between the gas and the dynamic evaporation surface.

[0009] According to another embodiment the dynamic heat exchanger comprises at least one liquid spraying member adapted to spray the liquid to be evaporated onto the dynamic evaporation surface, which cleans the dynamic evaporation surface or otherwise increases the heat transfer efficiency of the dynamic

evaporation surface.

[0001 0] According to another embodiment the dynamic heat exchanger comprises at least one liquid spraying member adapted to spray a second liquid or release a second gas, in addition to the liquid to be evaporated, onto the dynamic

evaporation surface, to reduce the friction that occurs between the gas and the dynamic evaporaHon surface, or to clean the dynamic evaporation surface or otherwise increase the heat transfer efficiency of the dynamic evaporation surface.

[0001 1 ] According to another embodiment the dynamic heat exchanger comprises a plurality of liquid spraying members placed in connection with the dynamic evaporation surface.

[0001 2] In yet other embodiments the dynamic heat exchanger could comprise at least a third cavity adapted to house a first humid gas and at least a fourth cavity adapted to house a second gas being less humid, wherein the first and third cavities are in fluid connection with each other. In embodiments with a plurality of cavities the cavities together makes up a dynamic heat exchanger.

[0001 3] A dynamic heat exchanger system comprising a dynamic heat exchanger is further provided. The dynamic heat exchanger system comprises at least one dynamic heat exchanging surface, and at least one liquid spraying member adapted to spray a liquid onto the at least one dynamic heat exchanging surface. The at least one liquid spraying member could be adapted to clean the at least one dynamic heat exchanging surface by spraying liquid thereon, which could remove any particles such as dust, microorganisms, particles which were contained as particles in the evaporated liquid or content dissolved in the liquid that crystallizes as the liquid evaporates, such as salts, [00014] According to one embodiment the dynamic heat exchanger system could comprises a dynamic evaporation surface. The at least one liquid spraying member could be adapted to spray a liquid adapted to evaporate onto the dynamic evaporation surface.

[00015] A method for preventing the accumulation of particles in an evaporative cooling system or removing particles from an evaporative cooling system is also provided. The evaporative cooling system comprises at least one evaporation surface rotatably mounted to a rotatable axis. The method comprises the step of rotating the rotatable axel and thus the evaporation surface rotatably mounted thereon, such that particles on the dynamic evaporation surface are removed by means of centrifugal force.

[0001 6] Please note that any embodiment or part of embodiment as well as any method or part of method could be combined in any way.

Brief description of drawings

[0001 7] The invention is now described, by way of example, with reference to the accompanying drawings, in which:

[0001 8] Fig. 1 shows an embodiment of an apparatus comprising two flows of gas in which one flow of gas is humidified by a flow of a liquid which is then

evaporated.

[0001 9] Fig. 2 shows one embodiment of a device for the addition of liquid to be evaporated in one of the flows of gas.

[00020] Fig 3 shows one embodiment of a device for the addition of liquid to be evaporated during the combined evaporation- and heat exchange procedure.

[0002 1 ] Fig 4 shows an alternative embodiment of a device for the addition of the liquid to be evaporated during the combined evaporation- and heat exchange procedure.

Detailed description

[00022] In the following a detailed description of embodiments will be given, in the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and are not in any way restricting the scope. Thus, any references to direction, such as "up" or "down", are only referring to the directions shown in the figures.

[00023] "Prevent" shall mean lessening of a certain factor. Thus, the lessening may or may not be complete.

[00024] Fig. 1 shows one embodiment of a dynamic heat exchanger for evaporative cooling in a cross-sectional side view. The dynamic heat exchanger is adapted for heat exchange between a first humid gas F l and a second gas F2 being less humid. The dynamic heat exchanger comprises a first 3a and second 4a cavity, separated from each other. The first cavity 3a is adapted to house a first humid gas Fl , and the second cavity 4a is adapted to house a second gas F2 being less humid. The first cavity 3a is partially enclosed by a dynamic evaporation surface 12 adapted to evaporate a liquid that comes in to contact with the dynamic evaporation surface 12 or otherwise being contained or evaporated within the cavity 3a, for cooling the dynamic evaporation surface 1 2. The dynamic

evaporation surface 12 is adapted to rotate such that particles on the dynamic evaporation 1 2 surface are removed by means of centrifugal force. According to the embodiment shown in fig . 1 , the entire dynamic heat exchanger is made up of a rotating part 1 , comprising a number of dynamic evaporation surfaces 12, here being flat discs 12, made of any suitable material, such as steel, aluminum or a polymer material, which are mounted on a rotation shaft 2 and which are intended to rotate together at appropriate speeds, proximally 1 500 rpm, around the axis 10 with the aid of an electric motor or similar. The discs 12 forms two separate system of cavities 3a,b and 4a,b,c that are internally interconnected, i.e 3a is in fluid connection with 3b, 4a is in fluid connection with 4b and 4c. Thus, two gases Fl and F2 are located in each of the respective cavity systems 3a, b and 4a,b,c without intermixing. Gas F l and gas F2 exchanges heat through the material 5 of the discs 1 2. In each level of the apparatus the gases Fl and F2 can move essentially radially; F l from inlet 8 to outlet 9 (solid arrows), F2 from the inlet ό to towards the center of the disc and outlet 7 (hollow arrows). According to the embodiment shown in fig. 1 the dynamic heat exchanger further comprises a conduit (20) adapted to transport the gas Fl into the dynamic heat exchanger and a liquid spraying member ( 14) adapted to spray a liquid into the conduit (20) for humidifying the gas F l before it enters the dynamic heat exchanger.

[00025] When two gases F l and F2 are delivered to the heat exchanger channels, a heat exchange takes place between the gases without the gases intermixing. Gas F l is humidified and therefore cooler than gas F2 and therefore cools gas F2. The humidification of the gas can either occur before the gas enters into the dynamic heat exchanger, or inside of the dynamic heat exchanger. In embodiments in which the gas Fl is humidified before the entry, or right in the inlet 8, the humidified gas enters the dynamic heat exchanger with zero rotational velocity and needs to be accelerated by the discs. The acceleration of the humidified gas creates a small friction between the surface of the disc and the gas which somewhat reduces the efficiency of the heat exchanger, In embodiments in which the dynamic heat exchanger comprises nozzles attached to the rotating part 1 (further disclosed with reference to fig. 4) the gas already has a rotational velocity which is the same as the radial velocity of the rotating discs 1 2, and thus do not need to be further accelerated by the discs 1 2, which reduces the amount of friction created by the connection between the discs 1 2 and the gas. The reduction of the friction means that no heat is created on the discs 1 2 and thus the heat exchange efficiency can be maximized. [00026] The rotation of rotating discs 1 2 around the axle 1 0 results in a centrifugal force that acts on any particles 1 1 that settles on the surface 1 3 of the discs 1 2. Thus any particles 1 1 such as dust, microorganisms, particles which were contained as particles in the evaporated liquid or content dissolved in the liquid that

crystallizes as the liquid evaporates, such as salts, will be radially ejected from the rotating discs 1 2 (dashed arrow), and an efficient cleaning action is thereby obtained. Particles 1 1 can conveniently be collected as they settle below, or in a filter, or allowed to be carried away with the gas flow.

[00027] Fig. 2 shows a dynamic heat exchanger according to an embodiment in which the dynamic heat exchanger further comprises at least one liquid spraying member 1 4 adapted to spray the liquid to be evaporated onto the dynamic evaporation surface 1 2. The liquid spraying member 14 is here schematically displayed as a nozzle or mouthpiece 14 for humidifying gas F_] with a liquid 1 that is intended to evaporate. The nozzle 1 is humidifying gas F, before it enters the cavity 4 and participates in heat exchange with gas F₂.

[00028] Figure 3 schematically shows another embodiment in which the liquid spraying member 16 is a nozzle or mouthpiece 16 that humidifies gas F, with a liquid as it enters the cavity 4.

[00029] Figure 4 shows the dynamic heat exchanger similar to the one disclosed with reference to fig. 1 , in a top view. According to the embodiment displayed in fig. 4 the dynamic heat exchanger comprises an arrangement of liquid spraying members 1 8 being nozzles or mouthpieces 1 8 being connected to the rotating disc 1 2. The arrow indicates the direction of rotation. In embodiments where the nozzles 1 8 are attached to the rotating part 1 (further disclosed with reference to fig. 1 ) and/or the rotating disc 1 2, the gas already has a radial velocity which is the same as the radial velocity of the rotating discs 1 2, and thus do not need to be further accelerated by the discs 12, which reduces the amount of friction created by the connection between the discs 1 2 and the gas. The reduction of the friction means that no heat is created on the discs 1 2 and thus the heat exchange efficiency can be maximized.

[00030] The rotation of rotating discs 1 2 around the axis 1 0 results in a centrifugal force that acts on any particles 1 1 that settles on the surface 1 3 of the discs 1 2. Thus any particles 1 1 such as dust, microorganisms, particles which were contained as particles in the evaporated liquid or content dissolved in the liquid that crystallizes as the liquid evaporates, such as salts, will be radially ejected from the rotating discs 1 2 (dashed arrow), and an efficient cleaning action is thereby obtained, Particles 1 1 can conveniently be collected as they settle below, or in a filter, or allowed to be carried away with the gas flow. Static heat exchangers for indirect evaporative cooling has the great drawback that growth of microorganisms such as fungi, algae and bacteria can occur in the canals of the heat exchangers that carry humidified air. The growth of microorganisms can occur to such an extent that channels of the heat exchanger are clogged or the heat transfer efficiency decreases. By rotating the dynamic evaporation surfaces 1 2 i.e. the discs 1 2, centrifugal forces works to a larger extent on the particles 1 1 than on the gases, thus pushing the particles 1 1 radially outwards keeping the surfaces clean such that the gas can flow freely. By keeping the surfaces clean the efficiency of the heat exchange is maintained.

[0003 1 ] The spraying of a liquid onto a dynamic heat exchanger surface could further be used to clean the dynamic heat exchanger surface, even if the dynamic heat exchanger surface is not used for evaporative cooling. For this purpose the liquid spraying member could be placed for example as described herein with relation to evaporative cooling, such that a liquid, which could be a solvent or other type of cleaning liquid, will be injected onto the at least one dynamic heat exchanger surface For cleaning the surface. [00032] Please note that any embodiment or part of embodiment as well as any method or part of method could be combined in any way. All examples herein should be seen as part of the general description and therefore possible to combine in any way in general terms.

Claims

1 . A dynamic heat exchanger for evaporative cooling characterized in that the dynamic heat exchanger is adapted for heat exchange between a first humid gas (FT) and a second gas (F₂) being less humid, wherein the dynamic heat exchanger comprises a first and second cavity (3a, 4a] separated from each other, wherein

• the first cavity (3a) is adapted to house a first humid gas (F,), and

• the second cavity (4a) is adapted to house a second gas (F₂) being less humid, wherein o the first cavity (3a) is partially enclosed by a dynamic evaporation surface (12) adapted to evaporate a liquid that comes in to contact with the dynamic evaporation surface ( 1 2), and wherein o the dynamic evaporation surface ( 1 2) is adapted to rotate such that particles on the dynamic evaporation surface ( 1 2) are removed by means of centrifugal force.

2. The dynamic heat exchanger according to claim 1 , wherein the dynamic heat exchanger further comprises at least one liquid spraying member (14; 1 6; 1 8) adapted to spray liquid into a gas flow entering the dynamic heat exchanger.

3. The dynamic heat exchanger according to claim 1 , wherein the dynamic heat exchanger further comprises at least one liquid spraying member (1 ; 1 6; 1 8) adapted to spray the liquid to be evaporated onto the dynamic evaporation surface (1 2) .

4. The dynamic heat exchanger according to claim 3, wherein the dynamic heat exchanger comprises a plurality of liquid spraying members ( 1 8) placed in connection with the dynamic evaporation surface (12).

5. The dynamic heat exchanger according to claim 1 , wherein the dynamic heat exchanger further comprises at least a third cavity (3b) adapted to house a first humid gas (F,) and at least a fourth cavity (4b) adapted to house a second gas (F₂) being less humid, wherein the first and third cavities (3a, 3b) are in fluid connection with each other, and the second and fourth cavities (4a, 4b) are in fluid connection with each other.

6. An dynamic heat exchanger system comprising a the dynamic heat exchanger comprising at least one dynamic heat exchanging surface, and at least one liquid spraying member adapted to spray a liquid onto the at least one dynamic heat exchanging surface.

7. The dynamic heat exchanger system according to claim 6, wherein the at least one liquid spraying member (14; 1 6; 1 8) is adapted to clean the at least one dynamic heat exchanging surface by spraying liquid thereon.

8. The dynamic heat exchanger system according to claim 6, wherein the at least one dynamic heat exchanging surface comprises a dynamic evaporation surface ( 1 2) and wherein the at least one liquid spraying member ( 14; 16; 1 8) is adapted to spray a liquid adapted to evaporate thereon.

9. A method for preventing the accumulation of particles in an evaporative cooling system or removing particles from an evaporative cooling system, the evaporative cooling system comprising at least one evaporation surface (12) rotatably mounted to a rotatable axel, wherein the method comprises the step of rotating the rotatable axel and thus the evaporation surface (1 2) rotatably mounted thereon, such that particles (1 1 ) on the dynamic evaporation surface (1 2) are removed by means of centrifugal force.