WO1999010686A1

WO1999010686A1 - Cooling cycle

Info

Publication number: WO1999010686A1
Application number: PCT/JP1998/003556
Authority: WO
Inventors: Nobuhiko Suzuki
Original assignee: Zexel Corporation
Priority date: 1997-08-21
Filing date: 1998-08-11
Publication date: 1999-03-04
Also published as: JPH1163694A

Abstract

A cooling cycle formed so as to improve the cooling performance thereof by allowing a liquid phase refrigerant to constantly exist in a gas-liquid separator even when a supercritical fluid is used as a refrigerant for a multiple effect cycle, wherein a main path (8) is formed by connecting a compressor (2), a radiator (3), a first throttle valve (4), a gas-liquid separator (5), a second throttle valve (6) and an evaporator (7) in series, and a bypass (9) for returning a gas phase refrigerant from the gas-liquid separator (5) to the compressor (2) is provided in this main path (8), the degree of opening of the first throttle valve (4) being reduced, when the liquid phase refrigerant in the gas-liquid separator becomes insufficient, to increase the degree of pressure reduction of the refrigerant passing through the gas-liquid separator, whereby the liquid phase refrigerant constantly exists in the gas-liquid separator.

Description

Details Cooling cycle Technical field

The present invention relates to a cooling cycle having a multi-effect cycle (gas injection cycle) in which a supercritical fluid such as co ₂ is used as a refrigerant and a gas-phase refrigerant from a gas-liquid separation device is returned to a compression chamber. .

Conventionally, as a cooling cycle having a multi-effect cycle (gas injection cycle), a configuration disclosed in Japanese Patent Application Laid-Open No. Hei 5-45007 has been known. This has a configuration as shown in FIG. 7, and will be described below with reference to this drawing. The cooling cycle 1 includes a compressor 2, a radiator 3, a first pressure reducing means 4, A main path 8 is formed by sequentially connecting the liquid separator 5, the second decompression means 6, and the evaporator 7, and a bypass path 9 connecting the gas-liquid separator 5 and the compressor 2 is provided. The gas-phase refrigerant separated by the gas-liquid separator 5 is returned to the compressor 2, thereby improving the cooling performance. Further, in the publication, a heat exchanger for exchanging heat between the refrigerant flowing out of the condenser 3 and the gas-phase refrigerant returning from the gas-liquid separator 5 is provided in the middle of the bypass path 9, There is also disclosed a configuration in which, even when a droplet refrigerant is mixed with a refrigerant, the refrigerant is returned to the compressor 2 as a complete gas state.

By the way, in recent years in which alternative refrigerants suitable for the natural environment are being sought, carbon dioxide refrigerant (CO 2), which has been used before using fluorocarbon gas, is attracting attention again. In such a cooling cycle using C02, since the critical temperature of C02 is 31 ° C, the high-pressure side line is used in the supercritical region, and it is necessary to obtain sufficient refrigeration performance. From high pressure It has been studied to increase the pressure of the side line to around 100 kg / cm ² and to use the above-described multi-effect cycle.

When C 02 is used as the refrigerant of the above-described multi-effect cycle, the state changes as shown by the solid line in FIG. 3 when viewed on a Mollier diagram. In other words, the high-temperature and high-pressure refrigerant compressed by the compressor 2 indicated by the point A is cooled without being liquefied by the heat radiator 3 and reaches the point B, and thereafter, the first pressure reducing means 4 returns to the intermediate pressure. The pressure is reduced to a gas-liquid mixed refrigerant indicated by point C, and separated into a gas-phase refrigerant and a liquid-phase refrigerant indicated by point D in the gas-liquid separator 5. The separated liquid-phase refrigerant is further decompressed by the second decompression means 6 to become low-pressure, low-temperature wet steam indicated by point E, is evaporated and vaporized by the evaporator 7 and reaches point F, and is compressed again by the compressor 2. Is done. At the same time, the gas-phase refrigerant separated by the gas-liquid separator 5 passes through the point H in the process of passing through the bypass passage 9, becomes a complete gas phase, and is returned to the compressor 2 to pass through the evaporator 7. Mix with gas phase refrigerant. That is, the gas-phase refrigerant compressed by the compressor 2 from the point F is mixed with the gas-phase refrigerant returned from the gas-liquid separator 5 when it is compressed to the intermediate pressure, and the gas-phase refrigerant from the point I to the point G is formed. And then returned to point A.

In such a multi-effect cycle, the gas-liquid separator 5 separates the refrigerant into a gas-phase refrigerant and a liquid-phase refrigerant. Although the flow rate of the refrigerant flowing through the evaporator 7 is reduced by the amount that the gas-phase refrigerant separated by the gas-liquid separator 5 is returned, the cooling capacity is increased by an amount corresponding to the enthalpy difference between the points C and D. be able to.

However, the state change of the supercritical fluid due to the above-described multi-effect cycle is formed when the cycle is properly controlled, and if the adjustment of the pressure reducing means is not performed properly, the cooling performance is reduced. this If the opening degree of the first pressure reducing means 4 is much larger than the opening degree of the second pressure reducing means 6, the pressure in the gas-liquid separator 5 becomes higher than the pressure on the radiator side (high pressure side). As shown in Fig. 8, point C reaches the gas-phase region and no liquid-phase refrigerant is formed in the gas-liquid separator. Is reduced as it is. In other words, the liquid refrigerant cannot be formed in the gas-liquid separator, so that the enamel ruby cannot be made smaller than the point C. As a result, the refrigeration effect (Q) is This is because it is decided by the ruby party on the side.

Such a phenomenon indicates that the cooling performance cannot be guaranteed if the existing cycle configuration is used as it is for supercritical fluids such as C 0 2, and therefore, how to solve this point An important point is whether supercritical fluids can be used effectively as alternative refrigerants.

Therefore, in the present invention, even when a supercritical fluid is used as a refrigerant for a multi-effect cycle, cooling is performed so that the liquid-phase refrigerant is always present in the gas-liquid separator to improve the cooling performance. The task is to provide a cycle. Further, since the cooling performance is improved as the temperature of the refrigerant entering the first pressure reducing means is lower, the present invention provides a cooling cycle in which the temperature of the refrigerant entering the first pressure reducing means is also improved. . Disclosure of the invention

In order to achieve the above object, a cooling cycle according to the present invention uses a supercritical fluid as a refrigerant, a compressor that pressurizes the refrigerant, and a first heat exchanger that cools the refrigerant pressurized by the compressor. A first decompression unit arranged downstream of the first heat exchanger and decompressing the refrigerant, and a gas-liquid separator for gas-liquid separation of the refrigerant decompressed by the first decompression unit. This damn A second decompression means for decompressing the liquid-phase refrigerant separated by the liquid separation device and a second heat exchanger for evaporating and evaporating the refrigerant decompressed by the second decompression means are sequentially connected by pipes. The gas-liquid separator is connected to the compressor by connecting the gas-liquid separator to the compressor, and a bypass path is provided to guide the gas-phase refrigerant separated by the gas-liquid separator to the compressor. The amount of pressure reduction by the first pressure reducing means is controlled in accordance with the amount of liquid refrigerant in the inside.

As the supercritical fluid, fluids such as C02 and ethylene having a critical temperature near normal temperature are used. As a method of controlling the amount of decompression by the first decompression means, a liquid-phase refrigerant in a gas-liquid separation device is used. Liquid-phase refrigerant in the gas-liquid separation device by a signal from a refrigerant amount detection sensor that detects the amount, or by calculation based on signals from a pressure sensor and a temperature sensor that detect the pressure and temperature in the gas-liquid separation device It is conceivable that the degree of pressure reduction by the first pressure reducing means is increased by detecting whether or not the pressure is insufficient and determining that the liquid phase refrigerant is insufficient.

Therefore, the high-temperature and high-pressure refrigerant that is pressurized by the compressor and becomes a supercritical state is cooled by the first heat exchanger and decompressed by the first decompression means to become an intermediate-pressure gas-liquid mixed refrigerant, and the gas-liquid separation Gas-liquid separation is performed inside the device. The gas-phase refrigerant separated by the gas-liquid separation device returns to the compressor through the bypass path, and the separated liquid-phase refrigerant is further decompressed by the second decompression means to become low-temperature low-pressure wet steam, In the evaporator, it is vaporized and led to the compressor.

The first decompression means adjusts the decompression amount according to the amount of the liquid-phase refrigerant in the gas-liquid separation device, so if the amount of the liquid-phase refrigerant in the gas-liquid separation device becomes insufficient, It is possible to avoid a situation in which the refrigerant flowing into the separation device becomes a gas-liquid mixed refrigerant and the liquid-phase refrigerant does not exist here. A reasonable level of cooling performance can be maintained while maintaining the state change as shown by the solid line in FIG.

To enhance the cooling performance, the temperature of the refrigerant flowing into the first pressure reducing means may be set as low as possible in addition to securing the liquid-phase refrigerant in the gas-liquid separator. That is, the gas-phase refrigerant separated on the refrigerant downstream side of the pressure reducing means may be heat-exchanged with the refrigerant flowing between the first heat exchanger and the first pressure reducing means. According to such a configuration, the refrigerant cooled in the first heat exchanger is further cooled by the gas-phase refrigerant downstream of the decompression means, and as a result, the refrigerant flowing into the evaporator is cooled. It is possible to increase the freezing effect by reducing the size of the ruby.

A configuration in which the gaseous phase refrigerant separated on the downstream side of the refrigerant of the decompression means exchanges heat with the refrigerant flowing between the first heat exchanger and the first decompression means is provided between the first and second decompression means. A gas-phase refrigerant returning from the gas-liquid separator provided to the compressor to the compressor on the inflow side of the first decompression means, and a second gas-liquid flow downstream of the evaporator refrigerant. A configuration is conceivable in which a separation device (accumulator) is provided, and the separated low-temperature gas-phase refrigerant exchanges heat with the refrigerant in the main path on the inflow side of the first pressure reducing means. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a configuration diagram showing a first configuration example of a cooling cycle according to the present invention. FIG. 2 is a control operation for controlling a first throttle valve by a control unit of the cooling cycle shown in FIG. FIG. 3 is a flowchart showing an example, FIG. 3 is a Moliere diagram of a cooling cycle according to the present invention, and FIG. 4 is a structural diagram showing a second configuration example of a cooling cycle according to the present invention. FIG. 5 is a configuration diagram showing a modification of the configuration example of FIG. 4, FIG. 6 is a configuration diagram showing a third configuration example of the cooling cycle according to the present invention, and FIG. 7 is a configuration diagram showing a conventional multi-effect cycle (gas injection cycle). FIG. 3 is a Mollier diagram showing a refrigerant state change that can be caused by a conventional multi-effect cycle (gas injection cycle). BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first configuration example of a cooling cycle 1. This cooling cycle 1 is composed of a compressor 2 for compressing a refrigerant, and a radiator 3 for cooling the refrigerant compressed by the compressor 2. A first throttle valve 4 disposed downstream of the radiator 3 on the refrigerant, a first gas-liquid separator 5 for separating the refrigerant decompressed by the first throttle valve 4 into gas and liquid, and a gas-liquid separator A second throttle valve 6 arranged downstream of 5, and a main path 8 formed by connecting an evaporator 7 for evaporating and evaporating the refrigerant decompressed by the second throttle valve 6 in series in this order. ing. The main path 8 is provided with a bypass path 9 having one end connected to the first gas-liquid separator 5 and the other end connected to an intermediate stage of the compressor 2. The separated gas-phase refrigerant is guided to the compressor 2 via the bypass path 9.

In this cycle, C 02 is used as the refrigerant, and the refrigerant compressed by the compressor 2 enters the radiator 3 as a high-temperature and high-pressure refrigerant, where it radiates heat and is cooled. This refrigerant is raised to about 10 O Kg / cm ² in the high pressure side line to be in a supercritical state, and is sent to the first throttle valve 4 without being liquefied by the radiator 3. Then, in the first throttle valve 4, the pressure is reduced to a pressure (intermediate pressure) higher than the pressure in the low-pressure line in which the evaporator 7 is disposed, and the reduced pressure refrigerant is a gas-liquid mixed refrigerant. For example, the gas-phase refrigerant and the liquid-phase refrigerant are separated in the first gas-liquid separator 5, and the gas-phase refrigerant is returned to the compressor 2 through the bypass passage 9, and the liquid-phase refrigerant is passed through the second throttle valve 6. The refrigerant is further reduced in pressure to become a low-temperature low-pressure (around 0 ° C., about 35 kg / cm ² ) gas-liquid mixed refrigerant, which is vaporized in the evaporator 7 to be gaseous and returned to the compressor 2. This state change is shown by the above-mentioned Moire diagram shown by a solid line in FIG.

The first gas-liquid separator 5 is provided with a sensor 10 for detecting whether or not the amount of the liquid refrigerant inside is in an insufficient state. However, in this example, the refrigerant pressure and the refrigerant temperature in the gas-liquid separator are detected, and the liquid level is indirectly detected from the detection results by calculation. . A signal relating to the liquid level detected by the sensor 10 is input to the control unit 11 and used to control the degree of engagement of the first throttle valve 4.

The control unit 11 includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), an input / output port (I / O), a drive circuit, and the like (not shown). According to the predetermined program, the processing of the flowchart shown in FIG. 2 is performed.

In the following, an example of the control operation of the first throttle valve 4 by the control unit 11 will be described. The control unit 11 performs the processing of this routine along with the operation of the cycle. And the signal from the sensor 10 for detecting the temperature and the temperature is stored in the RAM, and in the next step 52, based on the sampling time detected by the sensor 10, the amount of refrigerant in the gas-liquid separator ( L) is calculated.

And, the refrigerant amount (L) in the gas-liquid separator is zero or larger. If the predetermined amount is larger than the predetermined amount, the normal opening control is continued (steps 54, 56), and if L≤, the opening of the first throttle valve 4 is reduced to reduce the opening. Increase the pressure drop at the throttle valve 4 in (1) and set the point C in the Moliere diagram to be in the gas-liquid mixed refrigerant region as shown in Fig. 3 (Steps 54, 58) ). Then, in this configuration example, after the processes of Steps 56 and 58, the processes of Step 50 and below are repeated, and the refrigerant in the first gas-liquid separator is constantly monitored so that a shortage of the refrigerant does not occur. Has become.

Therefore, even when a supercritical fluid is used, it is possible to avoid a state in which the cooling performance is greatly reduced as shown in FIG. 8, and even when the refrigerant leaks from the cycle over time, The opening degree of the throttle valve 4 is automatically adjusted, so that the liquid-phase refrigerant in the first gas-liquid separator does not run out, and stable performance can be secured for a long period of time. In FIG. 4, a second configuration example of the present invention is shown, and different points from the above configuration example will be mainly described. In the same configuration, the same reference numerals will be given and the description will be omitted.

In this cycle configuration, an auxiliary heat exchanger 12 for exchanging heat between the refrigerant flowing through the main path 8 and the gas-phase refrigerant in the bypass path is provided between the radiator 3 and the first throttle valve 4, The refrigerant flowing out of the radiator 3 is further cooled by a lower-temperature refrigerant downstream of the first throttle valve 4.

According to such a configuration, the state change of the cycle is indicated by a broken line in FIG. 3, and the high-temperature and high-pressure refrigerant compressed by the compressor 2 indicated by the point A ′ is pointed to the point B by the radiator 3. However, it is further cooled to the point B ′ by the auxiliary heat exchanger 12 and reduced to the intermediate pressure indicated by the point C ′ by the first throttle valve 4 to become a gas-liquid mixed refrigerant, Gas-liquid separator 5 separates the refrigerant into a gaseous refrigerant and a liquid refrigerant indicated by point D '. The liquid-phase refrigerant is further decompressed by the second throttle valve 6 to become low-pressure, low-temperature wet steam indicated by the point E ', which is smaller than the point E, and then evaporated and vaporized by the evaporator 7. Reach point F. At the same time, the gas-phase refrigerant separated by the gas-liquid separator 5 absorbs heat from the refrigerant in the high-pressure side line in the auxiliary heat exchanger 12, passes through the point H ′, and turns into a complete gaseous state. The mixture with the gas-phase refrigerant shown at the point I ', which has been compressed to the intermediate pressure by step 2, mixes with the gas-phase refrigerant shown at the point G'. Then, the mixed gas-phase refrigerant is further pressurized by the compressor 2 and returned to the point A ′ again.

Therefore, according to such a multi-effect cycle, the opening degree of the first throttle valve 4 is adjusted by the control unit 11 to secure the liquid-phase refrigerant in the gas-liquid separator, and at the same time, the refrigeration effect Can be increased by an amount equivalent to the Enruby difference between points E and E '(Q2—Q1). In the above configuration, if it is desired to further add superheat control, the degree of engagement of the second throttle valve 6 may be adjusted in accordance with the temperature of the evaporator 7. For example, FIG. As shown, the second throttle valve 6 is a thermal expansion valve, the change in the degree of superheat of the refrigerant flowing out of the evaporator 6 is sensed by the temperature-sensitive cylinder 13, and the amount of refrigerant flowing into the evaporator 6 is adjusted. It is recommended to keep the degree of superheat constant.

FIG. 6 shows a third configuration example of the present invention. In this configuration example, a bypass path 9 connecting the first gas-liquid separator 5 and the compressor 2 is provided with a bypass path 9. 1 The configuration is the same as that shown in FIG. 1, except that a second gas-liquid separator (accumulator) 14 is arranged between the evaporator 7 and the compressor 2, and the refrigerant flowing out of the evaporator 7 The liquid-phase refrigerant mixed with the refrigerant is separated, and only the gas-phase refrigerant is returned to the compressor 2.

And, between the radiator 3 and the first throttle valve 4, the cooling of the high pressure side line is performed. An auxiliary heat exchanger 12 ′ for exchanging heat between the medium and the gas-phase refrigerant separated by the second gas-liquid separator (accumulator) 14 is provided, and the refrigerant flowing out of the radiator 3 evaporates. It is further cooled by the refrigerant on the downstream side.

According to such a configuration, as described above, the liquid-phase refrigerant can be secured in the first gas-liquid separator, and the refrigerant flowing out of the radiator 3 is further cooled to improve the cooling performance of the cycle. Operating efficiency can be improved. Industrial applicability

As described above, according to the present invention, in the case where a supercritical fluid is used as a refrigerant in a multi-effect cycle (gas injection cycle), a second phase is determined according to the amount of liquid-phase refrigerant in the gas-liquid separation device. By controlling the amount of decompression by the decompression means 1, it is possible to avoid a situation in which the liquid-phase refrigerant does not exist in the gas-liquid separation device, and it is possible to maintain a reasonable level of cooling performance.

In addition, even if the refrigerant leaks a little, the liquid-phase refrigerant is always present in the gas-liquid separation device, so that it is possible to prevent a situation in which the cycle balance changes over time and the cooling performance deteriorates.

Further, when the gas-phase refrigerant separated on the downstream side of the refrigerant of the decompression means is subjected to heat exchange with the refrigerant flowing between the first heat exchanger and the first decompression means, the first decompression means The temperature of the refrigerant flowing in can be further reduced, and the cooling performance of the cycle can be further improved.

Claims

Scope of Claim 1. Supercritical fluid as refrigerant,

A compressor that pressurizes the refrigerant, a first heat exchanger that cools the refrigerant pressurized by the compressor, and a second heat exchanger that is disposed downstream of the first heat exchanger and decompresses the refrigerant. (1) a pressure reducing means, a gas-liquid separator for gas-liquid separation of the refrigerant decompressed by the first pressure reducing means, and a second pressure reducing means for decompressing the liquid-phase refrigerant separated by the gas-liquid separator. And a second heat exchanger for evaporating and evaporating the refrigerant depressurized by the second decompression means.

A bypass path that connects the gas-liquid separator and the compressor and guides the gas-phase refrigerant separated by the gas-liquid separator to the compressor;

A cooling cycle, wherein the amount of reduced pressure by the first pressure reducing means is controlled in accordance with the amount of liquid-phase refrigerant in the gas-liquid separator.

2. The control of the amount of reduced pressure by the first pressure reducing means is performed by detecting the amount of liquid refrigerant in the gas-liquid separation device and determining that the amount of liquid refrigerant is insufficient. 2. The cooling cycle according to claim 1, wherein the amount of pressure reduction of the refrigerant by the cooling cycle is increased.

3. The control of the pressure reduction amount by the first pressure reduction means detects the pressure and temperature in the gas-liquid separation device, and when it is determined from these pressures and temperatures that the liquid refrigerant is insufficient. 2. The cooling cycle according to claim 1, wherein the amount of pressure reduction of the refrigerant by the first pressure reducing means is increased.

4. The gas-phase refrigerant separated on the refrigerant downstream side from the pressure reducing means, 2. The cooling cycle according to claim 1, wherein heat is exchanged with a refrigerant flowing between the first heat exchanger and the first pressure reducing means.

5. The cooling cycle according to claim 4, wherein the gas-phase refrigerant separated by the gas-liquid separator is heat-exchanged with a refrigerant flowing between the first heat exchanger and the first pressure reducing means.

6. Another gas-liquid separator is provided on the downstream side of the refrigerant of the second heat exchanger, and the separated gas-phase refrigerant is supplied between the first heat exchanger and the first decompression means. 5. The cooling cycle according to claim 4, wherein heat is exchanged with a refrigerant flowing through the cooling cycle.

7. The cooling cycle according to claim 1, wherein the amount of reduced pressure of the second pressure reducing means is adjusted according to a parameter related to the temperature of the second heat exchanger.

8. The superheat degree of the refrigerant flowing out of the second heat exchanger is detected, and the pressure reduction amount of the second pressure reduction means is adjusted so that the superheat degree is kept constant. The cooling cycle according to claim 7, wherein: