WO1999008053A1

WO1999008053A1 - Cooling cycle

Info

Publication number: WO1999008053A1
Application number: PCT/JP1998/003555
Authority: WO
Inventors: Nobuhiko Suzuki
Original assignee: Zexel Corporation
Priority date: 1997-08-12
Filing date: 1998-08-11
Publication date: 1999-02-18
Also published as: JPH1163686A

Abstract

A cooling cycle using a supercritical fluid as a refrigerant, capable of regulating the quantity of the refrigerant over a wide range, and adapted to reduce a required capacity of a refrigerant tank provided for increasing and decreasing the quantity of the refrigerant, wherein a main path (7) is formed by connecting a compressor (2), a radiator (3), an expansion valve (5) and an evaporator (6) in series, and a bypass path (9) is provided in the main path (7) so as to bypass the expansion valve (5) and is provided with a refrigerant tank (10) for storing the refrigerant therein, and on-off valves (11, 12) for opening and closing the inlet and the outlet of the refrigerant tank (10). The refrigerant in the refrigerant tank is cooled with the refrigerant which is circulating in the main path (7) and which has just passed through the expansion valve to keep the temperature in the refrigerant tank (10) lower than that in a high-pressure side line (7a), whereby a required quantity of refrigerant can be recovered.

Description

Details Cooling cycle Technical field

The present invention relates to a cooling cycle using a supercritical fluid, and more particularly to a cooling cycle including a refrigerant tank for adjusting a refrigerant amount in a cycle in a bypass path bypassing an expansion valve. Background art

In the search for alternative refrigerants suitable for the natural environment, carbon dioxide refrigerant (C02), which had been used earlier than using CFCs, is attracting attention again. In such a cooling cycle using C 0 2, the critical temperature of C 0 2

Since the temperature is 31 ° C, the high-pressure side line is used in the supercritical region, and it is necessary to obtain sufficient refrigeration performance, as shown in Fig. 4 of Japanese Patent Publication No. 7-186002. Cycle configuration is considered.

This is, as shown in FIG. 3 of the present application, a compressor 2 for increasing the pressure of the refrigerant, a radiator 3 for cooling the refrigerant, and a countercurrent heat for exchanging heat between the refrigerant flowing through the high-pressure line and the low-pressure line. It has a main path 7 having an exchanger 4, an expansion valve 5 for reducing the pressure of the refrigerant, and an evaporator 6 for evaporating and vaporizing the refrigerant. In this main path 7, the supercritical refrigerant pressurized by the compressor 2 is cooled by the radiator 3, and further cooled by the countercurrent heat exchanger 4 before entering the expansion valve 5. Then, the cooled refrigerant is decompressed by the expansion valve 5 to become wet steam, becomes a vapor-phase refrigerant in the evaporator 6, and then heat-exchanges with the high-pressure side refrigerant in the countercurrent heat exchanger 4 to be further heated. And returned to the compression chamber 2. Such a main route 7 is also described in the same gazette on page 4, lines 39-44, and on page 5, lines 38-48. As described above, a bypass path 9 for bypassing the expansion valve 5 is further provided, and a refrigerant tank 10 and valves 11 and 11 disposed on a high pressure side and a low pressure side with respect to the refrigerant tank 10 in the bypass path 9 are provided. In order to increase the amount of refrigerant in the main path 7, the valve 11 is closed and the valve 12 is opened to supply the refrigerant in the refrigerant tank to the main path Ί. When the amount of refrigerant in the main path 7 is to be reduced, the valve 11 is opened and the valve 12 is closed, and the refrigerant in the main path 7 is collected in the refrigerant tank 10.

However, in the above-described configuration, the refrigerant can be collected in the refrigerant tank 10 if the pressure in the refrigerant tank is lower than the pressure in the high-pressure side line at the time of collection. If the pressure is higher than or equal to, the refrigerant does not move from the main path 7 into the tank, and the refrigerant in the main path cannot be recovered.

Also, even when the pressure in the refrigerant tank is set to the intermediate pressure between the high-pressure line and the low-pressure line, a short time after opening the valve 11, the pressure in the refrigerant tank becomes high-pressure line. There is a concern that refrigerant pressure may not be sufficient for recovery of refrigerant.

Therefore, in the present invention, in a cooling cycle in which a supercritical fluid is used as a refrigerant and valves are provided on a refrigerant tank and outlet and inlet sides thereof to regulate the flow rate of the refrigerant in the main path, a refrigerant in the main path is used. The objective is to increase the range of adjustment of the amount of refrigerant in the main route, since it is possible to sufficiently collect the refrigerant. Another issue is to reduce the required volume of the refrigerant tank by increasing the efficiency of accumulating the amount of refrigerant in the refrigerant tank. 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, a radiator that cools the refrigerant pressurized by the compressor, and a radiator that A main path is formed by sequentially connecting pipes so as to include a pressure reducing means which is disposed downstream of the refrigerant and decompresses the cooled refrigerant, and an evaporator which heats the refrigerant depressurized by the pressure reducing means. A bypass path that bypasses the expansion valve in the main path; a refrigerant tank that stores refrigerant in the bypass path; and a control valve that adjusts a passage cross-section on a refrigerant upstream side and a refrigerant downstream side of the refrigerant tank. And a cooling means for cooling the refrigerant in the refrigerant tank is provided.

As the supercritical fluid, fluids such as C02 and ethylene whose critical temperature is around room temperature are used. Even when the control valve is an on-off valve that switches the bypass path to closed or closed, the cross section of the passage is continuous. May be a variable valve. As the cooling means, a cooling device independent of the main path may be separately attached to the tank to adjust the cooling capacity. May be configured to cool the refrigerant. Further, the refrigerant in the refrigerant tank may be constantly cooled or may be cooled only when necessary.

Furthermore, the cycle configuration of the main path includes at least a compressor, a radiator, a pressure reducing means, and an evaporator.For example, in order to further lower the temperature of the refrigerant flowing into the expansion valve, the cycle between the radiator and the expansion valve is required. A configuration in which a heat exchanger for exchanging heat between the refrigerant in the high-pressure side line and the refrigerant in the low-pressure side line is provided, or a configuration in which an accumulator is provided downstream of the refrigerant in the evaporator is included.

Therefore, according to such a configuration, the high-temperature and high-pressure refrigerant which is pressurized by the compressor and is brought into a supercritical state is cooled by the radiator and then decompressed. The pressure is reduced by the stage to become low-temperature, low-pressure wet steam, which is sent to the compressor after being evaporated and vaporized by the evaporator and pressurized again. The amount of the refrigerant flowing in the main path is adjusted by controlling the control valve of the bypass path to discharge the refrigerant in the refrigerant tank to the main path, or to recover the refrigerant from the main path. However, the refrigerant flowing into the tank from the main path during recovery is cooled by the cooling means and changes from a supercritical state to a subcritical state (liquid phase state). Therefore, it is possible to always keep the pressure lower than that required, and it is possible to reliably recover the required amount of refrigerant from the main path. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing a configuration example of a cooling cycle according to the present invention. FIG. 2 is a diagram showing a Mollier diagram of the cooling cycle shown in FIG. 1 together with a Mollier diagram of a conventional cycle. FIG. 3 is a diagram showing a configuration of a conventional cooling cycle. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, the cooling cycle 1 includes a compressor 2 for compressing the refrigerant, a radiator 3 for cooling the refrigerant, a countercurrent heat exchanger 4 for exchanging heat between the high-pressure side line and the low-pressure side line 4, and a refrigerant. The main path 7 includes an expansion valve 5 for reducing pressure and an evaporator 6 for evaporating and evaporating a refrigerant. The main path 7 connects the discharge side of the compressor 2 to the high-pressure passage 4 a of the countercurrent heat exchanger 4 via the radiator 3, and connects the outlet side of the high-pressure passage 4 a to the expansion valve 5. The path from the compressor 2 to the high pressure side of the expansion valve 5 is defined as a high pressure side line 7a. The low-pressure side of the expansion valve 5 is connected to an evaporator 6 via a cooling device 8 to be described later. It is connected to the low pressure passage 4 b of the container 4. The outflow side of the low-pressure passage 4b is connected to the suction side of the compressor 2, and the path from the low-pressure side of the expansion valve 5 to the compressor 2 is a low-pressure line 7b.

In this cooling cycle 1, C 0 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 supercritical refrigerant, where heat is radiated and cooled. . Thereafter, the heat is exchanged with the low-temperature refrigerant in the low-pressure side line 7 b in the counter-current heat exchanger 4 to be further cooled and sent to the expansion valve 5 without being liquefied. Then, the pressure is reduced by the expansion valve 5 to become low-temperature and low-pressure wet steam, and heat exchange with the air passing therethrough in the evaporator 6 to become gaseous, and thereafter, the high-pressure side line 7 in the countercurrent heat exchanger 4. It is heated by exchanging heat with the high-temperature refrigerant of a and returned to the compressor 2.

In the cooling cycle 1, one end is connected between the high-pressure passage 4a of the counterflow heat exchanger 4 and the expansion valve 5 with respect to the main path 7 described above, and the other end is connected to the expansion valve 5 and the evaporator 6 A bypass path 9 is provided to connect between the two. The bypass path 9 that bypasses the expansion valve 5 includes a refrigerant tank 10 for storing refrigerant and a passage on the high pressure side (between the refrigerant tank 10 and the high pressure side line 7 a) than the refrigerant tank 10. There is provided a first on-off valve 11 for opening and closing the valve, and a second on-off valve 12 for opening and closing the passage on the low pressure side (between the refrigerant tank 10 and the low pressure side line 7b).

In addition, a cooling device 8 that cools the coolant in the coolant tank 10 is provided between the expansion valve 5 and the evaporator 6 in the main path 7. The cooling device 8 is formed on a low-pressure pipe extending from the expansion valve 5. For example, a low-pressure pipe is wound around the refrigerant tank 10, or the low-pressure pipe and the side of the refrigerant tank 10 are brought into contact with each other. However, the refrigerant tank 10 may be constituted by a double pipe composed of an inner cylinder that stores the refrigerant and an outer cylinder that forms a passage around which the refrigerant flows. Alternatively, the refrigerant in the refrigerant tank may be constantly cooled by the low-temperature refrigerant after passing through the expansion valve 5. It is supposed to.

In the above configuration, when there is a need to increase the cooling capacity according to the heat load, or when there is a demand to operate the COP (coefficient of performance: refrigeration effect / compressor work) in the highest condition by increasing the high-pressure side pressure, etc. Closes the first on-off valve 11, opens the second on-off valve 12, opens only the low pressure side of the refrigerant tank 10, and discharges the refrigerant in the refrigerant tank 10 to the main path 7. As a result, the pressure of the high-pressure side line 7a increases, and the cooling capacity is increased.

Such a change in the state of the refrigerant is represented by A → B →

As shown by C → D → E → F → A, the supercritical high-temperature and high-pressure refrigerant compressed by the compressor 2 indicated by the point A is cooled to the point B by the radiator 3, and It is further cooled to point C by the flow type heat exchanger 4. Then, the pressure is reduced by the expansion valve 5 to become a low-temperature and low-pressure wet steam indicated by a point D. Thereafter, the heat is exchanged with the refrigerant in the refrigerant tank 10 by the cooling device 8, and the evaporator 6 evaporates and reaches the point E. . The refrigerant that has passed through the evaporator 6 is further heated to the point F by the countercurrent heat exchanger 4, and then compressed again by the compressor 2 to return to the point A.

In such a situation, if there is a request to keep the pressure of the high pressure side line 7a within the allowable range, or if it is necessary to lower the discharge temperature of the compressor 2, the cooling capacity will be reduced according to the heat load. If it is necessary to reduce the pressure, or if there is a request to reduce the high-pressure side pressure and operate at the maximum COP, the first on-off valve 11 is closed, the second on-off valve 12 is closed, and the refrigerant tank 1 is closed. Only the high pressure side of 0 is opened, and the refrigerant in the main path 7 is collected in the refrigerant tank 10. As a result, the pressure in the high pressure side line 7a decreases, and the cooling capacity decreases. In the conventional configuration in which the pressure in the refrigerant tank 10 is not adjusted in this process, the pressure in the refrigerant tank may be the same as that of the high-pressure side line 7a. No movement of the refrigerant to the refrigerant tank 10 occurs. Immediately after opening the first on-off valve 11, even if there is a pressure difference between the inside of the refrigerant tank and the high-pressure side line 7a, the pressure equilibrates after a while, and the high-pressure side line 7a In some cases, the refrigerant cannot be sufficiently recovered because the pressure drop P1 cannot be sufficiently large, and the refrigeration effect cannot be sufficiently reduced. In FIG. 2, this state is represented as a state change of A "→ B" → C "→ D" →→→ Κ "indicated by a chain line.

On the other hand, according to the present configuration, the refrigerant tank 10 is constantly cooled, the refrigerant in the tank is changed to liquid-phase refrigerant and accumulated, and the pressure in the refrigerant tank 10 is changed to the high-pressure side line 7 a Lower pressure is always maintained. For this reason, the amount of refrigerant recovered from the main path 7 to the refrigerant tank 10 can be increased, and the pressure fluctuation P2 of the high-pressure side line 7a can be made larger than P1, so that the refrigeration effect can be reduced. It can be reduced sufficiently. If this state is indicated by a broken line on the Moliere diagram, as shown in FIG. 2, it can be represented as a state change of A, → 'C' → Ώ '→ 、 → F → A', The adjustment range of the cooling capacity (Q to Q ′), that is, the adjustment range of the refrigerant amount can be made larger than the conventional adjustment range (Q to Q ″). Since they can be stored in a phased state, the required volume of the tank itself can be made smaller than that of the conventional one.

If cooling the refrigerant in the refrigerant tank with the refrigerant after passing through the expansion valve would greatly affect the refrigeration effect, the cooling device 8 should be provided as a separate cycle independent of the main path 7. Is also good. Industrial applicability

As described above, according to the present invention, in a configuration in which a refrigerant tank and control valves are provided on the outlet side and the inlet side thereof on the path bypassing the expansion valve of the main path to adjust the amount of refrigerant in the main path, Cools the refrigerant in the refrigerant tank and changes the refrigerant flowing from the main path into the refrigerant tank from the supercritical state to the subcritical state, so that the refrigerant tank is always kept at a lower pressure than the high-pressure line when recovering the refrigerant. With this configuration, the pressure in the high-pressure side line and the pressure in the refrigerant tank are not immediately equilibrated, and it is not difficult to collect the refrigerant, and the amount of refrigerant in the main path can be set to a desired amount. As a result, it is possible to adjust the amount of refrigerant in the main path at any time, regardless of whether the refrigerant is collected or not depending on the operating conditions of the cycle.

Further, since the refrigerant in the refrigerant tank is cooled to a subcritical state, the required volume is made smaller than that of the conventional refrigerant tank without requiring the same tank volume as the conventional one.

Claims

The scope of the claims

1. Supercritical fluid as refrigerant

A compressor that pressurizes the refrigerant, a radiator that cools the refrigerant pressurized by the compressor, a decompression unit that is disposed downstream of the radiator and that decompresses the cooled refrigerant, and a decompression unit A main path is formed by sequentially connecting pipes so as to include an evaporator for heating the refrigerant depressurized in

A bypass path for bypassing the pressure reducing means is provided in the main path, a refrigerant tank for accumulating refrigerant, and a control valve for adjusting a passage cross section on a refrigerant upstream side and a refrigerant downstream side of the refrigerant tank are provided on the bypass path. A cooling cycle, further comprising a cooling means for cooling the refrigerant in the refrigerant tank.

2. When increasing the amount of refrigerant in the main path, the control valve provided on the upstream side of the refrigerant in the refrigerant tank is closed, and the control valve provided on the downstream side of the refrigerant is opened. 2. The cooling cycle according to claim 1, wherein when reducing the amount, a control valve provided on a refrigerant upstream side of the refrigerant tank is opened, and a control valve provided on a refrigerant downstream side is closed.

3. The cooling cycle according to claim 1, wherein the cooling unit cools the refrigerant in the refrigerant tank with the depressurized refrigerant after passing through the decompression unit.

4. The cooling cycle according to claim 3, wherein the cooling means is formed by winding a low-pressure pipe of the main path around the cooling tank.

5. The cooling cycle according to claim 3, wherein the cooling unit is configured to connect a low-pressure pipe of the main path to the cooling tank.

6. The cooling cycle according to claim 3, wherein the cooling means comprises an inner cylinder having the cooling tank, and an outer cylinder having a passage through which the low-pressure refrigerant of the main path is formed. .

7. The main path includes a heat exchanger for exchanging heat between a high-pressure line refrigerant from the discharge side of the compressor to the decompression unit and a low-pressure line refrigerant from the decompression unit to the suction side of the compressor. 3. The cooling cycle according to claim 1, further comprising a vessel.