JPH09210480A - Two-stage compression type refrigerating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the temperature of the discharged gas with excellent responsiveness by interposing a parallel circuit of a capillary tube and a liquid injection valve to an inlet side of an intercooler, and controlling the liquid injection valve by the temperature of the discharged gas of a higher stage side compressor. SOLUTION: A capillary tube 11 is set to the resistance so as to secure the minimum liquid refrigerant flow rate required in an intercooler 6 and required to keep the degree of superheat of the higher stage side sucked gas to an appropriate value. A liquid injection valve 12 controls the temperature of the higher stage side discharged gas, and a temperature sensing cylinder 12a is installed on a higher stage side discharge pipe 23. When the temperature of the higher stage side discharged gas D is below the allowable value, the liquid injection valve 12 is closed. When the temperature of the higher stage side discharged gas is not less than the allowable value, the liquid injection valve 12 is operated, and controls the opening to increase the flow rate of the refrigerant flowing into the intercooler 6 to drop the temperature of the higher stage side discharged gas below the allowable value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-stage compression refrigeration system, and more particularly to temperature control of its discharge gas.

[0002]

2. Description of the Related Art As a conventional two-stage compression type refrigerating apparatus, for example, one having a refrigerating cycle configuration as shown in FIG. 4 is known. In addition, in FIG. 4, the arrow indicates the flow direction of the refrigerant. In this conventional configuration, 101 is a condensing unit, and the condensing unit 10
A plurality of cooling units 102 are connected to the high pressure side closing valve 130 and the low pressure side closing valve 131 of FIG.
Then, only one cooling unit is specified). High-pressure gas is discharged from the high-stage discharge port 103a of the two-stage compressor 103 installed in the condensing unit 101. This high-pressure gas is used for the condenser 104 and the receiver 10.
5, intercooler 106, high pressure side closing valve 130, 130,
It flows to the expansion valve 107 in the cooling unit 102.
Then, the pressure is reduced by the expansion valve 107, and the evaporator 108,
Low pressure side closing valve 131, 131, accumulator 109
And returns to the low pressure side suction port 101d. In the refrigeration cycle of the conventional refrigeration system, the basic circuit is constructed as described above.
Further, an intermediate pressure circuit is provided in the basic cycle. This intermediate voltage circuit will be described below. Branch pipe 121 is receiver 1
05 and the intercooler 106 are branched from a high-pressure liquid pipe 120. This branch pipe reaches the intercooler 106 via the electromagnetic valve 110 and the temperature-sensitive expansion valve 111. Then, the intermediate cooler 106 reaches the intermediate pressure gas pipe 122 that connects the low-stage side discharge port 103c and the high-stage side suction port 103b of the two-stage compressor 103. Furthermore, the solenoid valve 1 of this branch pipe
A pipe connecting 10 to the temperature-sensitive expansion valve 111 is connected to an intermediate pressure gas pipe 122 via a liquid injection valve 112. The above is the intermediate pressure circuit.

In the above refrigeration cycle, the solenoid valve 110
Is opened during operation of the refrigeration system, and the high-pressure liquid refrigerant is led to the branch pipe 121. The liquid refrigerant thus drawn out evaporates by itself, so that the intercooler 106 receives the liquid receiver 105.
The high pressure liquid refrigerant flowing from the evaporator to the evaporator 108 is supercooled. Further, in the intermediate pressure gas pipe 122, the low-stage side discharge port 103
The gas sucked into the high-stage suction port 103b from c is cooled. Here, in the temperature-sensitive expansion valve 111, a temperature-sensitive cylinder is arranged in the intermediate pressure gas pipe 122, and the liquid refrigerant flowing to the intermediate cooler 106 is maintained so as to keep the superheat degree of the refrigerant gas in the intermediate pressure gas pipe 122 constant. Controlling the amount. Further, the liquid injection valve 112 has its temperature sensitive cylinder 112a arranged in a high pressure gas pipe 123 extending from the high-stage side discharge port 103a to control the temperature of the high pressure gas refrigerant to a constant value. The condition of the control of the temperature-sensitive expansion valve 111 is set to be prioritized over the control of the injection valve 112. That is, the liquid injection valve 112 can be operated only when the temperature of the discharge gas of the high-pressure gas pipe 123 cannot be kept below the allowable value only by controlling the superheat degree of the suction gas of the high-stage side compressor by the temperature-sensitive cylinder tension valve 111. Is set to work.

[0004]

As described above, in the conventional two-stage compression type refrigerating apparatus, the temperature of the discharge gas of the high-stage compressor is kept within the allowable temperature range, so that the expensive temperature-sensitive expansion valve 111 is used. And a liquid injection valve 112 was required. In addition, one or a plurality of cooling units 10
In the case where there is a large load change due to the operation or suspension of some of the units of No. 2, the temperature-sensitive expansion valve 111 is set so that it has priority over the injection valve 112. Due to the reaction delay due to the heat capacity of the temperature sensing cylinder of the liquid injection valve 112, the response delay occurs in the control by these two valves, and abnormal overheating of the discharge gas and liquid back operation may occur.

The present invention has been made by paying attention to the problems existing in such conventional techniques. It is an object of the present invention to provide a two-stage compression type refrigerating apparatus which is inexpensive and can control discharge gas temperature with good responsiveness.

[0006]

In order to achieve the above-mentioned object, in the invention described in claim 1, the liquid refrigerant in the high pressure side pipeline is supercooled by the latent heat of vaporization of the liquid refrigerant in the intermediate pressure side pipeline. In a two-stage compression refrigeration system provided with a cooler, a branch pipe is provided from the high-pressure liquid pipe to the suction pipe of the high-stage compressor via the intermediate pressure side pipe line of the intermediate cooler, and the intermediate cooler of this branch pipe is provided. A parallel circuit of a capillary tube and a liquid injection valve is provided on the inlet side, and the liquid injection valve is controlled by the discharge gas temperature of the high-stage compressor.

According to a second aspect of the present invention, in the two-stage compression refrigerating apparatus according to the first aspect, the liquid injection valve is replaced with the discharge gas temperature of the high-stage side compressor by the superheat degree of the discharge gas. It is configured to control.

The two-stage compression type refrigerating apparatus constructed as described above uses one liquid injection valve and uses a capillary tube instead of the temperature sensitive expansion valve. Then, this capillary tube is necessary for making the liquid refrigerant flow rate required in the intercooler and the superheat degree (generally about 5 to 15 ° C.) appropriate for the low-stage side discharge gas as the high-stage side intake gas. The minimum liquid flow rate is secured. In addition, the liquid injection valve compensates for fluctuations in the liquid refrigerant flow rate due to operating conditions of the refrigerator. Therefore, the two-stage compression refrigerating apparatus of the present invention can control the temperature of the intake gas and the discharge gas at low cost and with high responsiveness without complicated condition settings for selectively using the two valves stepwise.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. In addition, in FIG. 1, the arrow indicates the flow direction of the refrigerant. Further, the symbols A to I are for explaining the states of the refrigerant, and the states of the refrigerant at the parts to which these symbols are attached correspond to the states at the parts to which the same symbols are attached in the Mollier diagram of FIG.

In the two-stage compression refrigerating apparatus shown in FIG. 1, a cooling unit 2 is connected to a condensing unit 1. The condensing unit 1 includes a two-stage compressor 3, a condenser 4, a liquid receiver 5, an intercooler 6, and a high-pressure side closing valve 3
0, 30, low-pressure side closing valves 31, 31 and the like are provided. The cooling unit 2 includes an evaporator 8, an expansion valve 7 and the like.

The refrigerant circuit includes a high-stage side discharge port 3a of the two-stage compressor 3, a condenser 4, a liquid receiver 5, a liquid pipe 20, an intercooler 6,
The high-pressure side closing valves 30, 30, the expansion valve 7, the evaporator 8, the accumulator 9, and the low-stage side suction port 3d are sequentially connected. In addition, the low-stage side discharge port 3c is the high-stage side suction port 3
connected to b. A branch pipe 21 is branched from the liquid pipe 20. The branch pipe 21 is connected to the intermediate pressure gas pipe 22 via the solenoid valve 10, the parallel circuit of the capillary tube 11 and the liquid injection valve 12, and the intermediate pressure side pipe line of the intermediate cooler 6.

Next, the refrigeration cycle will be described with reference to FIG. The refrigerant A sucked from the low-stage side discharge port 3d is compressed by the low-stage side compressor of the two-stage compressor 3, becomes an intermediate pressure gas refrigerant B, and is discharged from the low-stage side discharge port 3c. The low-stage discharge gas B is cooled by the liquid refrigerant H from the intercooler 6 to become C, and is sucked through the high-stage suction port 3b. The refrigerant C sucked into the high-stage side suction port 3b is compressed by the high-stage side compressor of the two-stage compressor 3, and the high-stage side discharge port 3
The gas refrigerant D having a high degree of superheat and high temperature and high pressure is discharged from a. The high-pressure gas D is cooled by the condenser 4 and becomes the liquid refrigerant E, which is stored in the liquid receiver 5. The refrigerant discharged from the liquid receiver 5 is cooled by the intercooler 6 and becomes the refrigerant F having a high degree of supercooling and enters the expansion valve 7. The liquid refrigerant F is adiabatically expanded by the expansion valve 7 to become a low-pressure liquid gas mixed refrigerant I and enters the evaporator 8. Then, it vaporizes and becomes low-pressure gas A having a superheat degree of 5 to 15 ° C. and returns to the low-stage side suction port 3d.

The solenoid valve 10 is open during the operation of this two-stage compression refrigeration system. Therefore, the liquid refrigerant E flows from the liquid pipe 20 to the branch pipe 21. This liquid refrigerant passes through the capillary tube 11 to become an intermediate-pressure liquid-gas mixed refrigerant G and enters the intermediate-pressure side passage of the intermediate cooler 6. Then, in the intercooler 6, the intermediate-pressure liquid-gas mixed refrigerant G exchanges heat with the high-pressure liquid refrigerant E. By this heat exchange, a part of the liquid refrigerant in the intermediate pressure liquid-gas mixed refrigerant is vaporized. Also,
The high-pressure liquid refrigerant E is cooled by the latent heat of vaporization and vaporization to become the liquid refrigerant F having a high degree of supercooling. On the other hand, the intermediate-pressure liquid-gas mixed refrigerant contains a partially unevaporated liquid refrigerant, but enters the intermediate-pressure gas pipe 22 in the state H in which the gas ratio is increased. Then, it is mixed with the low-stage side discharge gas B in the intermediate pressure gas pipe 22. During this mixing, the non-evaporated liquid refrigerant is vaporized and vaporized, and the low-stage side discharge gas B is cooled. The low-stage side discharge gas is
By this cooling, a gas C having an appropriate degree of superheat is formed and sucked into the high-stage compressor of the two-stage compressor 3.

In the above, the capillary tube 11
Is the minimum liquid refrigerant amount required in the intercooler 6 and the minimum liquid refrigerant flow rate required to maintain the superheat degree of the high-stage suction gas at an appropriate value (about 5 to 15 ° C.). The resistance is set so that Further, the liquid injection valve 12 controls the temperature of the high-stage side discharge gas, and the temperature sensitive tube 12 a is installed in the high-stage side discharge pipe 23.

Therefore, when the temperature of the high-stage discharge gas D is below the allowable value, the liquid injection valve 12 is closed. However, when the temperature of the high-stage side discharge gas is equal to or higher than the allowable value, the liquid injection valve 12 operates and the opening degree thereof is controlled to increase the flow rate of the refrigerant flowing to the intercooler 6, thereby increasing the high-stage side discharge gas. Control the gas temperature so that it is below the allowable value.

In the conventional two-stage compression refrigerating apparatus of FIG. 4 described above, when the temperature of the high-stage side discharge gas rises, the temperature-sensitive expansion valve 111 for adjusting the temperature of the high-stage side intake gas is operated, and still The liquid injection valve 112 for controlling the high-stage side discharge gas temperature was operated only when the rise in the discharge gas temperature was not suppressed yet. On the other hand, the two-stage compression refrigerating apparatus of the present invention, with respect to the change in the temperature of the discharge gas
Since the opening degree of the liquid injection valve 12 is immediately adjusted, it reacts sensitively to the change in the high-stage side discharge gas temperature.

Further, in the two-stage compression refrigerating apparatus of the present invention, the minimum amount required for steady operation is covered by the capillary tube 11, so the liquid injection valve 1
The capacity of 2 becomes small. Therefore, the responsiveness to the change in the operating condition due to the load change or the like is good. In addition, when the capillary tube 11 and the liquid injection valve 12 are replaced by a parallel circuit in the two-stage compression refrigeration apparatus of the present invention and only one liquid injection valve is provided, the capacity of the liquid injection valve becomes large. For this reason, in the discharge gas temperature control, a response delay of the liquid injection valve occurs during a transitional period such as load fluctuation. Therefore, there is a possibility that the high-stage side discharge gas may abnormally overheat or excessive liquid back may occur.

Next, a second embodiment will be described.
The second embodiment focuses on the fact that, in the refrigeration system, generally, when the discharge gas temperature abnormally rises, the superheat degree of the discharge gas also abnormally rises. By controlling the superheat degree of the discharge gas, , To prevent an abnormal rise in the discharge gas temperature. In the above-described first embodiment, the liquid injection valve 11 whose discharge gas temperature is controlled is used as the discharge gas temperature control valve, but the second embodiment is
This is different from the first embodiment in that a liquid injection valve 52 that controls the degree of superheat of the discharge gas is used as a control valve of the discharge gas temperature. The second embodiment will be described below with reference to FIG.

FIG. 3 shows the difference between the second embodiment and the first embodiment, and shows only the condensing unit 1. The same reference numerals are given to the same devices as those in the first embodiment.

As shown in FIG. 3, the liquid injection valve 52 is a type for controlling the degree of superheat, and has a temperature sensing cylinder 52a and a pressure equalizing pipe 52b. In the liquid injection valve 52, the temperature sensitive cylinder 52a is provided in the high-stage side discharge pipe, and the pressure equalizing pipe 52b is connected to the high-stage side discharge pipe.
The operation is performed when the superheat degree of the high-stage discharge gas exceeds a predetermined value.

Therefore, when the superheat degree of the high-stage side discharge gas exceeds a predetermined value, the liquid injection valve 52 operates and the high pressure liquid refrigerant flows to the intercooler 6 via the capillary tube 11 and the liquid injection valve 52. . The flow rate of the high-pressure liquid refrigerant to the intercooler increases. Then, the high-pressure liquid refrigerant is depressurized when passing through the capillary tube 11 and the liquid injection valve 52, and becomes a liquid-gas mixed refrigerant having an intermediate pressure. This mixed refrigerant, after cooling the high-pressure liquid refrigerant by the intercooler 6, flows into the intermediate-pressure gas pipe 22 while partially containing the liquid refrigerant. As a result, the two-stage compressor 3
The gas refrigerant sucked into the high-stage compressor is cooled, and the increase in the degree of superheat of the high-stage discharge gas is suppressed.

[0022]

Since the present invention is configured as described above, it has the following effects. According to the first and second aspects of the invention, the cost can be reduced by using the capillary tube and downsizing the liquid injection valve. Further, according to the first and second aspects of the present invention, control with good responsiveness can be obtained during a transitional period such as load fluctuation. Particularly, in the invention of claim 1, it is possible to prevent an abnormal rise in the discharge gas temperature. Further, according to the second aspect of the present invention, it is possible to prevent an abnormal increase in the superheat degree of the discharge gas, and consequently suppress an abnormal increase in the discharge gas temperature.

[Brief description of drawings]

FIG. 1 is a refrigerant circuit diagram of a two-stage compression refrigeration system according to a first embodiment.

FIG. 2 is a Mollier diagram of a refrigeration cycle in a two-stage compression refrigeration system.

FIG. 3 is a refrigerant circuit diagram of a two-stage compression refrigeration system according to a second embodiment.

FIG. 4 is a refrigerant circuit diagram of a conventional two-stage compression refrigeration system.

[Explanation of symbols]

1 ... Condensing unit, 2 ... Cooling unit, 3 ... Two-stage compressor, 3a ... High-stage side discharge port, 3b ... High-stage side suction port, 3c ... Low-stage side discharge port, 3d ... Low-stage side suction port,
4 ... Condenser, 5 ... Liquid receiver, 6 ... Intercooler, 7 ... Expansion valve, 8 ... Evaporator, 9 ... Accumulator, 11 ... Capillary tube, 12 ... Liquid injection valve, 12
a ... Temperature sensitive tube, 52 ... Liquid injection valve, 52a
… Temperature sensitive tube, 52b… Pressure equalizing tube.

Claims (2)

[Claims] 1. A two-stage compression refrigerating apparatus provided with an intermediate cooler for cooling the liquid refrigerant in the high-pressure side conduit with latent heat of vaporization of the liquid refrigerant in the intermediate-pressure side conduit, from the high-pressure liquid tube to the intermediate cooler. A branch pipe that leads to the suction pipe of the high-stage compressor via the pressure side pipe line is provided, and a parallel circuit of a capillary tube and a liquid injection valve is provided on the inlet side of the intercooler of this branch pipe, and this liquid injection A two-stage compression refrigeration system characterized in that the valve is controlled by the discharge gas temperature of the high-stage compressor. 2. The two-stage compression type according to claim 1, wherein the liquid injection valve is configured to be controlled by the superheat degree of the discharge gas instead of the discharge gas temperature of the high-stage compressor. Refrigeration equipment.