Improved vapour cycle system

Abstract

 @ The present invention relates to an improved vapour cycle system in particular, but not exclusively, for use in air conditioning and refrigeration plants.
According to the present invention, there is provided an improved vapour cycle system comprising:

a receiver for storing a working fluid;

an evaporator for receiving liquid working fluid from the receiver;

a heat exchanger for receiving an entraining fluid and heating said entraining fluid to produce a high pressure gas;

a jet pump for receiving said high pressure gas from said heat exchanger and drawing into it evaporated working fluid from said evaporator; and

means for feeding condensed working fluid to said receiver.

Description

[0001] The present invention relates to an improved vapour cycle system in particular, but not exclusively, for use in air conditioning and refrigeration plants. The vapour cycle system may be used to heat or to cool its surroundings, depending on the way it is connected.

[0002] The vapour cycle system of refrigeration has been in use for more than a century and its method of operation is based on the Carnot thermodynamic cycle. In this system a working fluid in its liquid state is stored in a receiver or reservoir. The liquid working fluid is fed into an evaporator over or through which a medium to be cooled is passed. The pressure in the evaporator is maintained below the desired saturation vapour pressure of the working fluid. The working fluid therefore extracts the latent heat needed to vaporise it from the medium to be cooled, thus vaporising the working fluid and cooling the medium.

[0003] The vapourised working fluid is drawn out of the evaporator and is compressed. The hot pressurised gas thus formed, which is a superheated vapour, is fed to a condenser, where the hot gas is cooled, for instance by passing a medium to be heated over or through the condenser, thereby causing the vaporised working fluid to condense to a liquid at a desired temperature and pressure. The condensed liquid working fluid is then fed to the receiver for recycling.

[0004] The vapour cycle system can be used for cooling or refrigeration, by use of the medium to be cooled, or for heating, by using the heat extracted during condensation of the superheated vapour.

[0005] The low pressure in the evaporator·and the compression of the vaporised working fluid is normally achieved by use of a mechanical compressor which may, for instance, be driven electrically or by an internal combustion engine.

[0006] Using a mechanical compressor is disadvantageous oecause it involves the use of moving parts, therefore requiring maintenance or replacement. Also the use of a mechanical compressor requires a large amount of energy, which can make the operation of the vapour cycle system expensive.

[0007] Despite these known disadvantages of the vapour cycle system, there have not been developed any commercial systems which do not use mechanical compressors.

[0008] There has also been proposed an absorption system of refrigeration in which the vaporised working fluid in the evaporator is entrained and absorbed in a flow of another fluid, thereby effecting evaporation of the working fluid and cooling of the medium. For instance, it has been proposed to use ammonia as the evaporating fluid and water as the entraining fluid. This system is disadvantageous because it necessitates the use of a mechanical pump to produce the flow of entraining fluid, although this pump requires less energy than a compressor for a similar vapour cycle system. Moreover, the mixture of evaporating fluid and entraining fluid must either be discarded or separated into its component fluids for recycling. This latter is another energy intensive step.

[0009] It is therefore an object of the present invention to provide an improved vapour cycle system which at least in part overcomes the disadvantages of the presently available systems.

[0010] According to the present invention, there is provided an improved vapour cycle system comprising:

a receiver for storing a working fluid;

an evaporator for receiving liquid working fluid from the receiver;

a heat exchanger for receiving an entraining fluid and heating said entraining fluid to produce a high pressure gas;

a jet pump for receiving said high pressure gas from said heat exchanger and drawing into it evaporated working fluid from said evaporator; and

means for feeding condensed working fluid to said receiver.

[0011] It is possible, by selecting a suitable design for the jet pump in conjunction with the selection of the working fluid and the system's operating conditions, to arrange for the material exiting from the jet pump to comprise substantially only condensed working fluid.

[0012] However, generally the material exiting from the jet pump will comprise vaporised working fluid which may also contain some condensed working fluid. It is therefore preferred that the system includes a condenser for receiving hot pressurised gas exiting from said jet pump to condense said working fluid, and for feeding said working fluid to said receiver.

[0013] The evaporator may be of any conventional type and receives heat from a medium to be cooled, such as water or air, which may be passed over or through it. The medium to be cooled may be used to cool or refrigerate the surroundings of the system.

[0014] Jet pumps, which are also known as suction pumps or ejectors, are well known. Generally a jet pump comprises a nozzle, a mixing chamber and a diffuser. The nozzle is connected to a source of high pressure gas which is injected into the mixing chamber at high velocity. This creates a pressure drop in the mixing chamber. In the present arrangement the high velocity flow of gas from the heat exchanger through the nozzle causes a reduction in the pressure in the evaporator, thereby allowing the evaporation of the working fluid and the cooling of the medium. The evaporated working fluid is then also entrained in the high velocity flow of gas which then passes to the diffuser where the velocity energy of the gas is converted into pressure energy. Therefore, the gas exiting from the jet pump is at high pressure and is heated by the latent heat of evaporation of the working fluid extracted from the medium to be cooled. Any of the know forms of jet pump may be used in the improved system of the present invention.

[0015] Any conventional condenser may be used, if necessary, to recondense the working fluid for recycle. The condenser may, for example, be located in a cooling medium, such as air or water, or may have the cooling medium passing over or through it. The cooling medium after receiving heat from the condenser may be used for instance for space heating.

[0016] If the working fluid is different from the entraining fluid, it will be necessary to separate the two fluids before they are recycled. However, it is preferred that the entraining fluid is the same as the working fluid and that the condenser is connected directly to the receiver.

[0017] Preferably, the jet pump is located in a heat balance chamber to ensure that the gas exiting therefrom is at optimum temperature and pressure.

[0018] The heat exchanger may receive all the heat needed to operate the system directly from an external heat source. Advantageously, the hot gas exiting from the jet pump is also passed through the heat exchanger which therefore supplies heat to both the entraining gas and the exiting hot gas.

[0019] It is envisaged that the working fluid and the entraining fluid will be one or a mixture of the fluorocarbon or chlorofluorocarbon gases commonly used in refrigeration systems. Such gases are available under the trade name "Freon".

[0020] The improved vapour cycle system of the present invention may, if desired, include further heat exchangers and/or condensers and/or heat balance chambers to optimise the thermal performance of the system or to utilize more effectively waste heat from external sources or the heated and cooled fluids produced by the system. The ways in which such components can be used will be readily apparent to those skilled in the art.

[0021] It will also be readily appreciated that the system will contain valves, such as one-way valves, control valves and bleed valves, for controlling the operation of the system. The way in which such valves will be used will be readily apparent to those skilled in the art.

[0022] It can be seen that the improved vapour cycle system of the present invention can be operated by providing only an external source of heat. This may be derived from exhaust heat from internal combustion engines or steam generating plant, waste heat from industrial processes or electricity generating stations, or from solar power.

[0023] The system does not require any compressors or pumps, and is therefore energy efficient. Moreover, it has no moving parts and is therefore less prone to break down and does not require frequent maintenance.

[0024] It is envisaged that the improved vapour cycle system of the present invention will be useful in cooling aircraft while they are on the ground and heating or cooling aircraft while in flight, for providing air conditioning and/or refrigeration on board ships and for providing air conditioning in factories, offices or homes. It is to be understood that air conditioning includes heating or cooling the ambient atmosphere.

[0025] One embodiment of an improved vapour cycle system of the present invention is now described, by way of example only, with reference to the accompanying drawing, which shows a schematic diagram of the system.

[0026] Referring to the drawing, there is shown a receiver 1 for storing a working fluid comprising a "Freon" fluorocarbon gas. The working fluid is fed to an evaporator 3 and also to a heat exchanger 5.

[0027] The evaporator 3 is connected to the mixing chamber of a jet pump 7 located in a heat balance chamber 9. The nozzle of the jet pump 7 is connected to the heat exchanger 5.

[0028] The outlet of the jet pump7isconnected to a secondary circuit in heat exchanger 5, the outlet of which is connected to a condenser 12, the outlet of which is connected to the receiver 1.

[0029] The system also includes an equalizing line 13 between the condenser 12 and the heat exchanger 5, having in it an automatic pressure valve 15. The valve 15 responds to varying pressure in the condenser 12 to prevent the system from reaching equilibrium and therefore stopping the cycle.

[0030] The system also includes other regulating valves in various of the lines to regulate the flows of liquid and vaporised working fluid in the system. The operation of these valves will be evident to a person skilled in the art and are therefore not referred to further herein.

[0031] The system may also include a second heat exchanger, for instance located in the line between the jet pump 7 and the first heat exchanger 5. Fluid heated in the second heat exchanger may be passed to a second circuit in the first heat exchanger to further heat the working fluid.

[0032] In use, working fluid is passed to the heat exchanger 5 and heated therein to produce vaporised fluid at high pressure and temperature (in a manner described below). Working fluid is also passed to the evaporator 3, over which a medium to be cooled is flowing.

[0033] The hot pressurised vapour is fed to the nozzle of the jet pump 7 and is injected as a high velocity stream into the mixing chamber. This causes a reduction in the pressure in the evaporator 3, and as the gas pressure falls, the temperature thereof falls, causing an initial cooling of the medium flowing over the evaporator. As the pressure is reduced and gas is drawn out of the evaporator 3, working fluid in the evaporator 3' vaporises, thus causing a second stage of cooling of the medium.

[0034] The vaporised working fluid in the evaporator 3 is entrained in the high velocity flow of working fluid in the mixing chamber. The mixed flows of working fluid pass to the diffuser of the jet pump 7 wherein the velocity energy is converted to pressure energy.

[0035] The mixed flow is then fed to the secondary circuit of heat exchanger 5 which receives heat from an external heat source, such as the exhaust gases from an internal combustion engine (not shown), wherein it is heated to above the saturation temperature required at condenser 12.

[0036] This mixed flow is then fed to the condenser 12, over which an external cooling medium is flowing, wherein it is cooled sufficiently to cause the working fluid to condense. The cooling medium is heated up by the condenser 12. The condensed working fluid is recycled to the receiver 1.

[0037] If the system is to be used as a refrigerating or cooling system, the medium to be cooled, after passing over the evaporator 3, is used to effect the cooling or refrigeration. If the system is to be used as a heating system, the external cooling medium after passing over the condenser 12 is used to effect the heating.

[0038] It car: thus be seen that the improved vapour cycle system of the present invention can be used without the need for mechanical pumps or compressors, has no moving parts, and can use waste heat or heat from readily available sources as the only energy input.

Claims

1. According to the present invention, there is provided an improved vapour cycle system comprising:

a receiver (1) for storing a working fluid;

an evaporator (3) for receiving liquid working fluid from the receiver (1);

a heat exchanger (5) for receiving an entraining fluid and heating said entraining fluid to produce a high pressure gas;

a jet pump (7) for receiving said high pressure gas from said heat exchanger (5) and drawing into it evaporated working fluid from said evaporator (3); and

means (12) for feeding condensed working fluid to said receiver (1).

2. The system of claim 1, including a condenser (12) for receiving hot pressurised gas exiting from said jet pump (7) to condense said working fluid, and for feeding said working fluid to said receiver (1).

3. The system of claim 1 or claim 2, wherein the jet pump (7) comprises a nozzle, a mixing chamber and a diffuser.

4. The system of any one of claims 1 to 3, wherein the working fluid and the entraining fluid are the same and are both supplied from the receiver (1).

5. The system of any one of claims 1 to 4, wherein the jet pump (7) is located in a heat balance chamber (9).

6. The system of any one of claims 1 to 5, arranged to pass hot gas exiting from the jet pump (7) to the heat exchanger (5).

7. The system of any one of claims 1 to 7, wherein the working fluid is a fluorocarbon or a chlorofluorocarbon.

8. The system of claim 2 or any claim dependent thereon, arranged so that the cooling medium for the condenser (12) is used for space heating.

9. The system of any one of claims 1 to 7, wherein the medium cooled by the heat exchanger (5) is used for cooling or refrigerating.

10. A method of operating a vapour cycle system wherein a jet pump is used to create a pressure drop in an evaporator containing a working fluid.

Drawing