DE69612546T2 - DEVICE FOR HEAT TRANSFER USING AIR - Google Patents

Description

The present invention relates to a device for heat transfer using air according to the preamble of claim 1.

Such a device has been disclosed in US-A-4 665 715, corresponding to EP-A-0 192 501. This US-A-4 665 715 discloses the following method and device therefor: by means of a suction line, outside air is sucked in by means of a compressor, which leads the air via a line to a heat exchanger. From this exchanger, the air is led via a line to a water extraction device. From the water extraction device it goes to an expansion turbine and from the expansion turbine it goes to the housing space. From the housing, the air is allowed to flow via a line to the heat exchanger. From this heat exchanger, it is allowed to flow outside.

Another device for heat transfer by means of air is disclosed in US-A-4 769 051. According to US-A-4 769 051, air is taken in from the environment by means of an engine and passed to a compressor via a first heat exchanger. After the compressor, the air is passed to a regenerative heat exchanger via a second heat exchanger. After the regenerative heat exchanger, the air flows through a water separator, through a filter and a unit before reaching a turbine. From the turbine, the air flows through a load heat exchanger and then through the heat exchanger to leave the cycle via the unit into the environment. The extraction of heat from the air within the closed environment, the target space, takes place by means of the load heat exchanger. The second air cycle is not in fluid communication with the first air cycle.

JP-A-57 174 692 discloses the use of balls made of glass, steel or the like as heating medium in a regenerative heat exchanger.

Yet another device for heat transfer by means of air is disclosed in the journal "VMT VOEDINGSMIDDELTECHNOLOGIE", vol. 25, no. 21, 8 October 1992 (NL) Zeist, pp. 75-77 "Koelproces zonder CFK's: de air cycle [Cooling process without CFC' s: the air cycle] " by RJM van Gerwen and SM van der Sluis. The device described therein is designed as a cooling plant, that is to say the first device comprises a compressor and the second device comprises an expander, the first part of the regenerator is intended to absorb heat from the air and the second part of the regenerator is intended to release heat to the air. The outlet of the second part of the regenerator is connected to the inlet of the first device or the compressor via a heat exchanger of conventional design. As can be seen from Fig. 1 of this publication, it is also possible to place the heat exchanger downstream of the compressor. Such an apparatus has the disadvantage that at refrigeration temperatures below 0ºC the regenerator freezes, with the consequence that de-icing agents must be added. In order to prevent the regenerator from freezing, it is necessary for the gas used, such as air, to either contain a little moisture or to be used at a relatively high temperature. In the case of the apparatus described in the journal, however, the gas or air flows through the target space or refrigeration space. This is essential for the "Joule-Brayton" system and distinguishes this system from conventional closed systems using CFCs, ammonia and the like. This means that a change in the gas composition has a direct effect on the contents of the target space. Changing the temperature of the gas is not possible because this would lead to an unacceptable change in temperature. The apparatus, which is designed as a heat pump, has the disadvantage that the Heat exchangers freeze at outside temperatures below 0ºC, which means that de-icing agents must be added.

The purpose of the present invention is to provide an improved device which eliminates the need for freezing and the additional de-icing agents that result therefrom, increases the energy efficiency of the device, increases the thermal efficiency of the regenerator, better preserves the quality of the frozen products and which can be implemented more simply and inexpensively.

This purpose is achieved with a device as described above having the features as described in claim 1.

By omitting the heat exchanger between the outlet of the regenerator and the inlet of the first device for changing the air pressure, i.e. by drawing air into the first device directly from the environment and blowing the air out of the outlet of the regenerator directly into the environment, the temperature difference across this heat exchanger, which is no longer present, is prevented, with the result that the device can operate with a higher energy efficiency. In the device designed as a heat pump, the heat exchanger, which is no longer present, is prevented from freezing, with the result that the heat pump can continue to operate even at outside temperatures below 0ºC.

According to the invention, the transfer of both free and latent heat, the latter in the form of condensation, freezing, sublimation, desublimation, thawing or evaporation, takes place in the regenerator. The result is that the energy exchange in the regenerator is extremely efficient. Due to the fact that the air flow which is blown into the cooling room is saturated with water vapor, frozen food products do not dry out and the quality is maintained. It has been found that in order to achieve a sufficiently large heat exchanger surface, it is advantageous according to the invention if the equivalent diameter D of the particles of the particles consisting of material between 1 and 25 mm. The equivalent diameter D is defined here as

D =3 6V/π

where V is the volume of a particle.

The regenerative heat exchanger of the device according to the invention works very well based on the design requirement that the physical properties of the particulate material, the equivalent diameter of the particulate material and the dimensions of the heat exchanger must satisfy the following relationship:

B = λDλ/2mAirCpL² < 0.1

where:

A = total heat-exchanging surface of the particles in a compartment in m²

D = mean equivalent diameter of the particles in m

λ = heat transfer coefficient of the particles in W/mK

mAir = air flow rate in kg/s

Cp = specific heat of air in J/KgK

L = length of the bed in m.

The change in the state of the regenerator now preferably takes place in the regenerative heat exchanger, the material consisting of particles meeting the requirements as described in claims 4-8. Tests have shown that with such materials no blockage of the bed occurs, while on the other hand optimal regenerative properties are achieved. In particular, it is particularly advantageous according to the invention if the ratio of the volume of the material consisting of particles to the volume occupied by the bed is between 0.2 and 0.8. With such a ratio it is possible to achieve a good flow through the bed and to simultaneously achieve a good exchange of free and latent heat as well as steam.

Very good results can be achieved especially by using spherical particles.

Based on the above formula, many types of materials can be used as the particulate material. However, it is particularly advantageous according to the invention if the particulate material comprises one or more of the following materials: ceramic material, glass and/or hygroscopic material. Here, the particles themselves can consist of one or more of these materials, but it is also conceivable to design the bed from a mixture of different particles, for example a mixture of glass particles and ceramic particles.

According to a useful embodiment, the regenerative heat exchanger comprises a switching device to alternately connect one compartment to one or the other tube system, the regenerative heat exchanger comprises two compartments which can be connected to one or the other tube system at the same time. Such a regenerative heat exchanger can be operated essentially continuously, with the particulate material absorbing heat from the fluid flow passing through it in one compartment, while in the other compartment heat is transferred by the particulate material to the fluid flow passing through it. Once the particulate material has absorbed sufficient free and latent heat in one compartment and the particulate material has transferred its free and latent heat to the other compartment, the two fluid flows and the two compartments can be mutually switched. This switching process can then be repeated continuously.

According to an embodiment which is energetically advantageous, the device further comprises a compression device, the outlet of which is connected to the inlet of the first compression device, optionally via a heat exchanger for exchanging heat with the environment Advantageously, the compression device and the expansion device in this case each comprise a rotor, it being possible to drive the two rotors by means of a conventional shaft. Such a combined compression-expansion unit (a so-called turbocharger) generally operates optimally at speeds at which it is difficult to provide the work required for the conventional shaft. This required additional work can be provided by means of the further compression device.

The device according to the invention can be used very advantageously in a cooling system or heat pump for cooling or heating a target room, wherein the target room is preferably in open connection with the cooling system or the heat pump.

The invention is explained in more detail below with reference to a few exemplary embodiments shown in the drawings, where:

Fig. 1a shows a schematic representation of a cooling system according to the invention;

Fig. 1b shows a schematic representation of a so-called heat pump according to the invention;

Fig. 2a shows a cooling system according to another embodiment of the invention;

Fig. 2b shows a heat pump according to another embodiment.

Embodiment of the invention;

Fig. 3 shows schematically a regenerative heat exchanger according to the invention of the so-called static type; and

Fig. 4 shows schematically a regenerative heat exchanger according to the invention of the so-called rotary type.

Fig. 1a schematically shows a cooling system 30 according to the invention, which is open on both sides.

In Fig. 1b a heat pump 20 is shown which is open on both sides.

The cooling system 30 and the heat pump 20 operate according to the Joule-Brayton process, which in its simplest form consists of an adiabatic compression step, an isobaric heat exchange step and an adiabatic expansion step.

The cooling system 30, which is open on both sides according to Fig. 1a, works as follows:

Air sucked in from the environment (atmosphere) is fed via the inlet 51 to a compressor 32. The air is compressed in the compressor 32, during which process the pressure and temperature of the air increase. The compressed air is then fed to an expander 31 (expansion device) via an intermediate line system 6, 7 in which a regenerative heat exchanger is installed, which is described with reference to Fig. 3. Expansion of the air takes place in the expander 31, during which process the pressure and temperature of the air decrease. The expanded, cooled air is fed via a line 46 to the target room 34 to be cooled. This target room 34 to be cooled can be a substantially closed room, such as a cold store or a freezer store. The cooled air flows from the line 46 unhindered into the cooling room 34. During this process, the supplied cold air will spread in the target room, with the result that uniform cooling of the target room 34 can be realized. Air from the target room 34, which is still relatively cold or cool, is discharged from the target room 34 via a return system 4, 5. Before this air, which is still relatively cold or cool, flows unhindered into the environment, it is passed through the regenerative heat exchanger to exchange heat and moisture with the air flow to be supplied to the target room 34. During this process, the air discharged from the target room via the return system 4, 5 absorbs heat and moisture from the air to be supplied to the target room 34.

In Fig. 1b, a so-called heat pump according to the invention is shown schematically. In short, the operation of this heat pump is as follows:

Air is sucked in from the environment via the line 25. This air is expanded in an expander 22. During this process, the pressure and temperature of the air decrease. The air is then fed to a compression device 23 via an intermediate duct system 6, 7 in which a regenerative heat exchanger is incorporated, which will be described with reference to Fig. 3. In the regenerative heat exchanger, the temperature of the air is increased, while the pressure will remain substantially the same. As soon as the air reaches the compressor 23, it is compressed, during which process the pressure and temperature increase. The heated air is then fed via a duct 24 to the target room 21 to be heated. The warm air flows substantially unhindered into the target room 21, the result of which is that uniform and effective heating of the room is made possible. Air is discharged from this target room 21 via a return line system 4, 5, wherein the air, before flowing into the outside air via a line 5, flows through the regenerative heat exchanger 1 in order to preheat the air which is to be supplied to the target room 21 via the intermediate line system 6, 7.

Fig. 2a shows another embodiment of a cooling system according to the invention. This cooling system 40 according to Fig. 2a corresponds generally to the cooling system 30 according to Fig. 1a. The difference is essentially that in the cooling system 40 according to Fig. 2a the compression takes place in two steps. There is a first compression step, which takes place in the further compression device 41, and a second compression step, which takes place in the first compression device 33. Intermediate cooling between the two steps preferably takes place by means of a heat exchanger 43, which is installed in the line system 42, 44 between the two compressors 41 and 33. In this heat exchanger 43, the air which has been passed through the line system 42, 44 is cooled with the aid of the ambient air which is fed to the heat exchanger 43 via the line 49 and is discharged from the heat exchanger 43 into the environment again via the line 57. The compressor 33 and the expander 31 form a so-called turbocharger, which is driven by a conventional Shaft 45 is driven. Such turbochargers generally operate at speeds of 50,000 to 150,000 rpm. The additional compressor 41 makes it possible to deliver sufficient work.

Leakage flows can be counteracted by keeping the pressure in the room to be cooled at substantially the same pressure as in the environment. This can be achieved by installing a compression device in the air flow leaving the target room. Preferably, this compression device is located in line 5. The regulation of this compression device can be based on the pressure difference between the environment and the target room or on the volume flow in the line systems 4, 5 and 51, 42, 44, 6, 7, 46.

The cooling temperature or the cooling capacity of a cooling system 40 according to Fig. 2a can advantageously be regulated by regulating the speed of the compressor 41, for example by means of a speed controller for a rotor.

Fig. 2b shows another embodiment of a heat pump according to the invention. This heat pump 29 according to Fig. 2b largely corresponds to the heat pump 20 according to Fig. 1b. The difference is essentially that in the heat pump 29 according to Fig. 2b the compression takes place in two steps. There is a first compression step, which takes place in the further compression device 26, and a second compression step, which takes place in the first compression device 23. Intermediate cooling or heating between the compression steps, as in the cooling system according to Fig. 2a, is not necessary in the heat pump 29 according to Fig. 2b. The compressor 23 and the expander 22 form, corresponding to the compressor 33 and the expander 31 of the cooling system 40 according to Fig. 2a, a so-called turbocharger, which is driven by a conventional shaft 28. As has already been explained, such turbochargers generally operate at speeds of 50,000 to 150,000 rpm. The additional compressor 26 makes it possible to deliver sufficient work.

Leakage flows in the heat pump 29 can also be prevented by keeping the pressure in the room 21, which is to be heated, at substantially the same pressure as in the environment. This can be achieved by installing a compression device, such as a fan, in the air flow leaving the target space 21. Preferably, this compression device is located in line 5. The regulation of this compression device can be based on the pressure difference between the environment and the target space 21 or on the volume flow in the line systems 4, 5 and 25, 6, 7, 27, 24.

The heating temperature or the heating power of the heat pump 29 according to Fig. 2b can advantageously be regulated by regulating the air flow speed of the compressor 26, for example by means of a speed controller for a rotor.

Fig. 3 shows an example of a regenerative heat exchanger 1 according to the invention. This heat exchanger comprises two compartments 2 and 3, each of which is provided with a fixed bed of particulate material 10. As shown, its particles 11 are essentially spherical, but differently shaped, for example non-uniform, particles are also quite conceivable.

The operation of the regenerative heat exchanger 1 can be described as follows:

Fluid, such as air, to be supplied to the target space 21, 34 is supplied to the regenerative heat exchanger via line 6, passed to the left compartment 3 by means of valve 9, passed through the packed bed therein and passed towards the target space via valve 8 and line 7. Fluid, such as air, which has been discharged from the target space is passed through the right compartment 2 via line 4 and valve 8, passed through the packed bed of particulate material 10 and discharged from the regenerative heat exchanger 1 via valve 9 and line 5. By simultaneously rotating the positions of the valves 8 and 9 by 90º to the positions shown in dashed lines, the effect is achieved that the fluid flow which goes towards the target space is directed through the right compartment (instead of through the left compartment) and that the fluid flow which is discharged from the target space is directed through the left compartment (instead of through the right compartment). By allowing this rotation of the valves 8, 9 to take place according to a law to be determined in more detail (which will depend, among other things, on the process conditions, the physical properties of the particulate material, etc.), the effect is achieved that alternately the bed always absorbs heat in one compartment while the bed in the other compartment releases heat.

It has been found that the bed of such particulate material is also very suitable for binding to self-condensation or precipitation, such as deposition of moisture or ice, and then releasing it to the other fluid flow. In this way, one of the fluid flows can be dehumidified. This can bring considerable advantages, especially when such a regenerative heat exchanger is used in refrigeration plants. The air to be supplied to the refrigeration plant is hereby simultaneously cooled and dehumidified in the regenerative heat exchanger, whereby it is possible to remove the moisture through the fluid flow discharged from the refrigeration space after the valves have been switched, while the temperature of the particulate material is simultaneously reduced. In this way, the regenerative heat exchanger 1 is protected from being blocked as a result of deposition of moisture and/or ice.

A further advantage is that the air flow which has been dehumidified in the regenerative heat exchanger 1 will not form any deposits of moisture or ice in further process steps in a cooling system or even a heat pump, so that here too the device is protected from being blocked.

Fig. 4 shows a regenerative heat exchanger 70 according to the invention of the so-called rotary type. This regenerative heat exchanger 70 consists essentially of a cylinder 74 which is divided into compartments which extend in its longitudinal direction. The cylinder 74 shown in Fig. 4 comprises three compartments 71, 72 and 73 which are formed by installing three partition walls 75, 76 and 77 in the Cylinder 74 can be obtained, the partitions of which are secured to one another along the central longitudinal axis of the cylinder 74. Each compartment thus obtained is filled with a bed 10 of particulate material 11. The cylinder 74 is arranged to be rotatable about the axis 78. Supply lines 4, 6 and discharge lines 5, 7 are arranged at the ends of the cylinder 74. The lines 4 and 5 here form part of one line system, while the lines 6 and 7 form part of another line system. By rotating the cylinder about its axis of rotation 78, while fluid, for example air, flows through the line systems 4, 5 and 6, 7 respectively, the effect is achieved that the various compartments are successively incorporated into one line system (for example 4, 5) or the other line system (for example 6, 7). By dividing the cylinder 74 into three or more compartments, it is easy for a compartment to be connected to only one piping system at a time, so that the fluid flow from the different piping systems cannot be directly mixed with each other. The operation of the regenerative heat exchanger 70, as will be clear, otherwise takes place in accordance with the operation described with reference to Fig. 3 for the regenerative heat exchanger 1. It will then also be clear that the regenerative heat exchanger 1 of Figs. 1a, 1b, 2a and 2b can easily be replaced by a regenerative heat exchanger 70 of the rotary type.

It will be clear that many variants of the regenerative heat exchanger shown schematically in Fig. 3 are conceivable. Thus, for example, the supply line 6 can be a discharge line, with discharge line 7 then becoming a supply line. Accordingly, it is possible to reverse the flow direction in lines 4 and 5. Instead of the valves 8, 9, many other switching devices for allowing one or the other fluid flow to flow alternately through the respective compartments are also conceivable. A variant is also conceivable in which the regenerative heat exchanger comprises a preferably cylindrical compartment which rotates about its axis. The particulate material in this compartment is then exposed in turn to one or the other fluid flow.

Numerous variants of the heat pump and cooling system shown in Fig. 1a, 1b and Fig. 2 are also conceivable. Consequently, the heat exchangers, compressors, expanders, etc. can also be connected upstream, intermediately or downstream. In their simplest form, such devices should comprise at least one expansion device, at least one compression device and at least one regenerative heat exchanger arranged between a compression device and an expansion device.

Claims (11)

1. Device for heat transfer by means of air, comprising successively in the direction of air flow: - first device (22, 32) for changing the air pressure in a first direction; - a first part of a regenerative heat exchanger (1) for exchanging heat from the air in a first direction; - second device (31, 23) for changing the air pressure in a second direction, the second direction being opposite to the first direction; - a second part of the regenerative heat exchanger (1) for exchanging heat from the air in a second direction which is opposite to the first direction ; the device further comprising a target space (21, 34) into which heat is to be transferred, the target space being provided with an air inlet and an air outlet, wherein the air inlet of the target space (21, 34) is connected to the second device (31, 23); wherein the air outlet of the target space (21, 34) is connected to the second part of the regenerative heat exchanger; wherein the first device is provided with an inlet (51, 23) that draws air exclusively from the environment; and wherein the outlet (5) of the second part of the regenerative heat exchanger (1) is connected exclusively to the environment, characterized in that the first and second parts of the regenerative heat exchanger (1) are functionally interchangeable and comprise a bed of particle-based Include material for the exchange of free heat, latent heat and moisture; characterized in that the equivalent diameter (D) of the particles (11) of the particulate material is between 1 and 25 mm, the equivalent diameter (D) being determined according to D = 3 6V/π is determined, where V is the volume of a particle, and that the physical properties of the particulate material (10), the equivalent diameter of the particulate material (10) and the dimensions of the heat exchanger are designed to satisfy the following relationship: B = λDλ/2mAirCpL² < 0.1 where: A = total heat-exchanging surface of the particles in Cp = one compartment in m² D = mean equivalent diameter of the particles in m λ = heat transfer coefficient of the particles in W/mK mLUft = mass flow of air in kg/s specific heat of air in J/KgK L = length of the bed in m. 2. Device according to claim 1, comprising a cooling system, wherein the first device (33) comprises a compressor, the second device (31) comprises an expander, the first part of the regenerator is intended to absorb free and latent heat from the air, and the second part of the regenerator is intended to release free and latent heat to the air. 3. Device according to claim 1, comprising a heat pump, wherein the first device comprises an expander (22), the second device comprises a compressor (23), the first part of the regenerator is designed to release free and latent heat to the air, and the second part of the regenerator is designed to absorb heat from the air. 4. Apparatus according to any preceding claim, wherein the ratio (ε) of the volume of particulate material in the regenerator to the volume occupied by the bed is between 0.2 and 0.8. 5. Device according to one of the preceding claims, wherein the particles (11) of the particulate material are substantially spherical. 6. A device according to any preceding claim, wherein the particulate material comprises a ceramic material. 7. A device according to any preceding claim, wherein the particulate material comprises glass. 8. A device according to any preceding claim, wherein the particulate material comprises a hygroscopic material. 9. Device according to one of the preceding claims, further comprising a compression device (41; 26), the outlet (42; 27) of which is connected to the inlet (44; 27) of the compression device (33; 23), optionally via a heat exchanger (43) for exchanging heat with the environment. 10. Device according to claim 9, wherein the compression device (33; 23) and the expansion device (31; 22) each comprise a rotor, it being possible to drive the two rotors by means of a conventional shaft (45; 28). 11. Device according to one of claims 9 or 10, further comprising a compression device, such as a fan, for Adjusting the pressure difference between the environment and the target room. Legend: 1 regenerative heat exchanger, regenerator 2 compartment 3 compartment 4 return system 5 outlet; return system; line 6 intermediate line system 7 intermediate line system 8 valve 9 valve 10 (fixed) bed of particulate material 11 (made of) particulate material 20 heat pump 21 target chamber 22 first device; expander; expansion device 23 second device; inlet; compressor; compression device 24 line; line system 25 line system 26 compression device; compressor 27 outlet; inlet; line system 28 conventional shaft 29 heat pump 30 cooling system 31 second device; expansion device; expander 32 first device; compressor 33 first device; compression device 34 target chamber; cooling chamber 40 cooling system 41 compression device 42 outlet; line system 43 heat exchanger 44 inlet; line system 45 conventional shaft 45 pipe; pipe system 49 pipe 51 inlet; pipe system 57 pipe 70 regenerative heat exchanger 71 compartment 72 compartment 73 compartment 74 cylinder 75 partition wall 76 partition wall 77 partition wall 78 axis