JPH1163694A - Refrigeration cycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigeration cycle having improved cooling performance by putting a liquid phase refrigerant in a gas/liquid separator even when a supercritical fluid is used as a refrigerant of a multiple stage cycle. SOLUTION: A main passage 6 is constructed by connecting a compressor 2, a heat radiator 3, a first throttle valve 4, a gas/liquid separator 5, a second throttle valve 6, and an evaporator 7 through piping, on which main passage 6 a bypass passage 9 is provided for returning a gas refrigerant from the gas/ liquid separator 5 to the compressor 2. When the liquid phase refrigerant in the gas/liquid separator is insufficient, opening of the first throttle valve 4 is reduced to increase the degree of pressure reduction of the refrigerant passing through the opening whereby the liquid phase refrigerant is present in the gas/ liquid separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Field of the Invention The invention uses a supercritical fluid such as CO ₂ as a refrigerant, Ta Kou cycle so as to return the gas refrigerant from the gas-liquid separator to the compression chamber (gas injection cycle) Cooling cycle provided.

[0002]

2. Description of the Related Art Conventionally, a cooling cycle having a multi-effect cycle (gas injection cycle) is disclosed in
A configuration disclosed in JP-A-45007 is 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 gas-liquid It has a main path 8 constituted by sequentially connecting the separator 5, the second decompression means 6, and the evaporator 7, and has a bypass path 9 connecting between the gas-liquid separator 5 and the compressor 2. The gas-phase refrigerant separated by the gas-liquid separator 5 is
And the cooling performance is thereby improved. 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 droplet refrigerant is mixed in the compressor 2, the refrigerant is returned to the compressor 2 as a complete gas state.

[0003] In recent years, in search of alternative refrigerants suitable for the natural environment, carbon dioxide refrigerant (CO ₂ ), which has been used before using fluorocarbon gas, has attracted attention again. Such a cooling cycle using CO ₂
Since the critical temperature of CO ₂ is 31 ° C., the high pressure side line is configured to be used in a supercritical region.
It has been studied to increase the g / cm ^{2 to} around g / cm ² and to use the multi-effect cycle described above.

[0004] CO _{2 is used} as a refrigerant in the above-described multi-effect cycle.
In the case where is used, when viewed in a Moliere diagram, a state change as shown by a solid line in FIG. 3 is exhibited. That is, the high-temperature and high-pressure refrigerant compressed by the compressor 2 indicated by the point A is cooled without being liquefied by the radiator 3 and reaches the point B, and then the first pressure reducing means 4 reduces the pressure to the intermediate pressure. Been C
The refrigerant becomes a gas-liquid mixed refrigerant indicated by a point, and is separated into a gas-phase refrigerant and a liquid-phase refrigerant indicated by a 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 and low-temperature wet steam indicated by point E, vaporized by the evaporator 7 to point F, and compressed by the compressor 2 again. You. At the same time, the gas-phase refrigerant separated by the gas-liquid separator 5 passes through the point H in the course of passing through the bypass path 9, becomes a complete gas phase, and is returned to the compressor 2 and passes through the evaporator 7. Mix with phase refrigerant. That is, from the point F, the compressor 2
When compressed to the intermediate pressure, the gas-phase refrigerant compressed at the point is mixed with the gas-phase refrigerant returned from the gas-liquid separator 5 to be in a gas-phase state from the point I to the point G, and then returned to the point A. It is.

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

[0006]

However, the above-mentioned state change of the supercritical fluid due to the multi-effect cycle is formed when the cycle is properly controlled. This leads to a decrease in cooling performance. This is because the opening degree of the first pressure reducing means 4 is the second degree.
When the opening degree of the pressure reducing means 6 is very large, the pressure in the gas-liquid separator 5 approaches the pressure on the radiator side (pressure on the high-pressure side line), and as shown in FIG. This is because the point reaches the gas phase region and no liquid phase refrigerant is formed in the gas-liquid separator, and the gas pressure refrigerant is decompressed by the second pressure reducing means 6 as it is. That is, since the liquid-phase refrigerant cannot be formed in the gas-liquid separator, the enthalpy cannot be made smaller than the point C. Consequently, the refrigeration effect (Q) depends on the enthalpy on the outlet side of the radiator 3. This is because it is determined.

[0007] Such a phenomenon indicates that the cooling performance cannot be guaranteed if the existing cycle configuration is used as it is for a supercritical fluid such as CO _2. An important point is whether or not the fluid can be effectively used as a substitute refrigerant.

Therefore, in the present invention, even when a supercritical fluid is used as a refrigerant in a multi-effect cycle, a cooling system is designed so that the liquid-phase refrigerant always exists 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.

[0009]

To achieve the above object, a cooling cycle according to the present invention uses a supercritical fluid as a refrigerant, a compressor for increasing the pressure of the refrigerant, and a compressor for increasing the pressure of the refrigerant. A first heat exchanger for cooling, a first decompression unit arranged downstream of the first heat exchanger for decompressing the refrigerant, and a refrigerant decompressed by the first decompression unit. A gas-liquid separator for liquid separation, a second decompression means for decompressing the liquid-phase refrigerant separated by the gas-liquid separation apparatus, and a second heat for evaporating the refrigerant decompressed by the second decompression means. A main path is formed by sequentially connecting pipes so as to include an exchanger, and the gas-liquid separator and the compressor are connected to each other to guide the gas-phase refrigerant separated by the gas-liquid separator to the compressor. A bypass path is provided, and the first reduction is performed according to the amount of liquid refrigerant in the gas-liquid separation device. It is characterized by controlling the pressure reduction amount by means (claim 1).

As the supercritical fluid, a fluid such as CO ₂ or ethylene having a critical temperature near normal temperature is used. As a method for controlling the amount of pressure reduction by the first pressure reducing means, a liquid phase in a gas-liquid separation device is used. The liquid-phase refrigerant in the gas-liquid separator is obtained by a signal from a refrigerant amount detection sensor that detects the amount of refrigerant, or by a calculation based on signals from a pressure sensor and a temperature sensor that detect pressure and temperature in the gas-liquid separator. It is conceivable that the degree of pressure reduction by the first pressure reducing means may be increased by detecting whether or not the pressure is insufficient and determining that the liquid refrigerant is insufficient.

Therefore, the high-temperature and high-pressure refrigerant which is pressurized by the compressor to be in 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. Gas-liquid separation is performed in the gas-liquid separation 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 guided to the compressor.

The first decompression means adjusts the decompression amount in accordance with the amount of the liquid-phase refrigerant in the gas-liquid separation device. Therefore, when the amount of the liquid-phase refrigerant in the gas-liquid separation device becomes insufficient, Therefore, it is possible to avoid a situation in which the refrigerant flowing into the gas-liquid separation device becomes a gas-liquid mixed refrigerant and there is no liquid-phase refrigerant, thereby maintaining the state change as shown by the solid line in FIG. A reasonable level of cooling performance can be maintained.

In order 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 downstream side of the refrigerant from 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 enthalpy of the refrigerant flowing into the evaporator is reduced. To improve the freezing effect.

The structure in which the gaseous phase refrigerant separated on the downstream side of the refrigerant from the decompression means exchanges heat with the refrigerant flowing between the first heat exchanger and the first decompression means is constituted by first and second decompression. A gas-phase refrigerant returning to the compressor from a gas-liquid separator provided between the first and second pressure reducing means, and a heat exchange with a refrigerant in a main path at an inflow side of the first decompression means, and a second refrigerant at a downstream side of the refrigerant of the evaporator. It is conceivable to provide a gas-liquid separation device (accumulator) and heat exchange the separated low-temperature gas-phase refrigerant with the refrigerant in the main path on the inflow side of the first pressure reducing means.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, cooling cycle 1
The cooling cycle 1 includes a compressor 2 for compressing a refrigerant, a radiator 3 for cooling the refrigerant compressed by the compressor 2, and a refrigerant downstream of the radiator 3. The first throttle valve 4, a first gas-liquid separator 5 for separating the refrigerant decompressed by the first throttle valve 4 into gas and liquid, and a second gas-liquid separator 5 disposed downstream of the gas-liquid separator 5. A throttle valve 6; an evaporator 7 for evaporating the refrigerant decompressed by the second throttle valve 6
Are connected in series in this order. 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 compressed gas-phase refrigerant is guided to the compressor 2 via the bypass path 9.

In this cycle, CO ₂ is used as a 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 100 kg / c in the high pressure side line.
The pressure is raised to about m ² and is 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 evaporator 7
Higher than the pressure of the low pressure line (intermediate pressure)
If the depressurized refrigerant is a gas-liquid mixed refrigerant, the refrigerant is separated into a gaseous refrigerant and a liquid-phase refrigerant in the first gas-liquid separator 5, and the gaseous refrigerant is passed through the bypass passage 9 to the compressor. 2
The liquid-phase refrigerant is further reduced in pressure by the second throttle valve 6 to become a low-temperature and low-pressure (about 0 ° C., about 35 kg / cm ² ) gas-liquid mixed refrigerant, and is vaporized in the evaporator 7 to be gaseous. It is returned to the compressor 2. This state change is shown by the above-described Mollier 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. Although it is possible to directly detect the level, in this example, the refrigerant pressure and the refrigerant temperature in the gas-liquid separator are detected, and the liquid level is indirectly detected by calculation from these detection results. I have. A signal related to the liquid level detected by the sensor 10 is input to the control unit 11,
It is used to control the opening of the first throttle valve 4.

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

In the following, the control unit 11
The control unit 11 performs the processing of this routine in accordance with the operation of the cycle, and inputs a signal from the sensor 10 for detecting pressure and temperature in step 50. It is stored in the RAM, and in the next step 52, the amount of refrigerant (L) in the gas-liquid separator is calculated based on the sampling data detected by the sensor 10.

If the refrigerant amount (L) in the gas-liquid separator is larger than a predetermined amount α set to zero or larger, normal opening control is continued (steps 54 and 5).
6) If L ≦ α, the opening degree of the first throttle valve 4 is reduced to increase the pressure drop at the first throttle valve 4, and the point C shown in the Mollier diagram is shown in FIG. (Steps 54 and 5).
8). Then, in this configuration example, the processing of step 50 and subsequent steps is repeated after the processing of steps 56 and 58, and the first
The refrigerant in the gas-liquid separator is constantly monitored to prevent shortage of the refrigerant.

Therefore, even when the 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 to prevent the refrigerant from leaking out of the cycle with time. The opening degree of the first 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.

FIG. 4 shows a second configuration example of the present invention, in which mainly different points from the above-mentioned configuration example will be 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 in 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. In addition, 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 as shown by the broken line in FIG. 3, and the high-temperature and high-pressure refrigerant compressed by the compressor 2 indicated by the point A ' Is cooled to the point,
Is further cooled to the point B ', the pressure is reduced to the intermediate pressure indicated by the point C' by the first throttle valve 4, and the refrigerant becomes gas-liquid mixed refrigerant. And a liquid-phase refrigerant indicated by. The liquid-phase refrigerant is further decompressed by the second throttle valve 6 and becomes low-pressure low-temperature wet steam indicated by a point E ′ having a smaller enthalpy than the point E.
The evaporator 7 evaporates and reaches the point F. At the same time, the gas-phase refrigerant separated by the gas-liquid separator 5 is supplied to the auxiliary heat exchanger 12.
Absorbs heat from the refrigerant in the high-pressure side line to become a complete gaseous state via point H ', and is mixed with a gas-phase refrigerant indicated by point I' compressed to an intermediate pressure by the compressor 2 and indicated by point G ' It is in a gaseous state. 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 of the first throttle valve 4 is controlled by the control unit 1.
As a result, the liquid-phase refrigerant is secured in the gas-liquid separator by the adjustment of 1, and at the same time, the refrigeration effect can be increased by the capacity corresponding to the enthalpy difference (Q2-Q1) between the points E and E '.

In the above configuration, if it is desired to add superheat control, the degree of opening of the second throttle valve 6 may be adjusted in accordance with the temperature of the evaporator 7. As shown in the figure, the second throttle valve 6 is a heat-sensitive expansion valve, and a change in the degree of superheat of the refrigerant flowing out of the evaporator 6 is sensed by the temperature-sensitive cylinder 13 to adjust the amount of refrigerant flowing into the evaporator 6. It is preferable 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 between the first gas-liquid separator 5 and the compressor 2 is illustrated. 1
The configuration is the same as that shown in FIG.
A second gas-liquid separator (accumulator) 14 is arranged between the second gas-liquid separator and the liquid-phase refrigerant mixed with the refrigerant flowing out of the evaporator 7, and only the gas-phase refrigerant is returned to the compressor 2. It has become.

Then, between the radiator 3 and the first throttle valve 4, heat exchange is performed between the refrigerant in the high-pressure side line and the gas-phase refrigerant separated by the second gas-liquid separator (accumulator) 14. An auxiliary heat exchanger 12 'is provided, and the refrigerant flowing out of the radiator 3 is further cooled by the refrigerant on the downstream side of the evaporator.

According to such a configuration, as described above, the liquid-phase refrigerant can be ensured in the first gas-liquid separator, and the refrigerant flowing out of the radiator 3 is further cooled to reduce the cycle cooling performance. And operation efficiency can be improved.

[0030]

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), the amount of decompression by the first decompression means is controlled in accordance with the amount of liquid-phase refrigerant in the gas-liquid separation device, and the gas-liquid A situation in which the liquid-phase refrigerant does not exist in the separation device can be avoided, and a reasonable level of cooling performance can be maintained.

Also, even if the refrigerant leaks a little, the liquid-phase refrigerant always exists in the gas-liquid separation device, so that the cycle balance changes with time and the cooling performance does not deteriorate. Can be.

Further, when the gaseous phase refrigerant separated on the downstream side of the refrigerant from the pressure reducing means is subjected to heat exchange with the refrigerant flowing between the first heat exchanger and the first pressure reducing means, the first pressure reducing means is used. The temperature of the refrigerant flowing into the means can be further reduced, and the cooling performance of the cycle can be further improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first configuration example of a cooling cycle according to the present invention.

FIG. 2 is a flowchart illustrating an example of a control operation of controlling a first throttle valve by a control unit of the cooling cycle illustrated in FIG. 1;

FIG. 3 is a Mollier diagram of a cooling cycle according to the present invention.

FIG. 4 is a configuration diagram showing a second configuration example of the cooling cycle according to the present invention.

FIG. 5 is a configuration diagram illustrating a modified example 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.

FIG. 7 is a configuration diagram showing a conventional multi-effect cycle (gas injection cycle).

FIG. 8 is a Mollier diagram showing a refrigerant state change that can be caused by a conventional multi-effect cycle (gas injection cycle).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cooling cycle 2 Compressor 3 Radiator 4 First throttle valve 5 1st gas-liquid separator 6 2nd throttle valve 7 Evaporator 8 Main path 9 Bypass path 10 Sensor 11 Control unit 12, 12 'Auxiliary heat exchange Vessel 14 second gas-liquid separator

Claims (2)

[Claims] 1. A compressor that uses a supercritical fluid as a refrigerant and pressurizes the refrigerant, a first heat exchanger that cools the refrigerant pressurized by the compressor, and a refrigerant that is higher than the first heat exchanger. A first decompression means disposed on the downstream side for decompressing the refrigerant, a gas-liquid separation device for gas-liquid separation of the refrigerant decompressed by the first decompression means, and a liquid phase separated by the gas-liquid separation device Forming a main path by sequentially connecting pipes so as to include a second decompression means for decompressing the refrigerant and a second heat exchanger for evaporating the refrigerant decompressed by the second decompression means; A bypass path is provided to connect the liquid separation device and the compressor, and to guide the gas-phase refrigerant separated by the gas-liquid separation device to the compressor, according to a liquid-phase refrigerant amount in the gas-liquid separation device, A cooling cycle wherein the amount of pressure reduction by the first pressure reducing means is controlled. 2. The method according to claim 1, wherein the gaseous phase refrigerant separated downstream of the pressure reducing means is supplied to the first heat exchanger and the first heat exchanger.
2. The cooling cycle according to claim 1, wherein heat is exchanged with a refrigerant flowing between said cooling means and said pressure reducing means.