JPH0730962B2 - Two-stage compression refrigeration cycle - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a two-stage compression refrigeration cycle in which a circulating refrigerant of a refrigeration cycle is compressed by a low-stage compression mechanism and a high-stage compression mechanism.

2. Description of the Related Art Conventionally, when the ratio (compression ratio) between the evaporation pressure and the condensation pressure in the refrigeration cycle is large, such as in a low-temperature refrigeration system or a high-temperature heat pump, in order to prevent the discharge temperature from rising and improve the compressor efficiency. A two-stage compression refrigeration cycle in which two one-stage compressors are installed in series is widely used. In this case, the gas discharged from the low-stage compressor is directly or indirectly heat-exchanged with a high-pressure liquid refrigerant or an intermediate-pressure two-phase refrigerant to be cooled, and then sucked into the high-stage compressor, where the high pressure Is compressed and discharged,
Cycle through the cycle. By doing so, the intake gas temperature of the high-stage compressor is lowered, and its discharge temperature is prevented from rising. Also, by appropriately setting the compression ratios of the low-stage and high-stage compressors, it is possible to operate under conditions with good compressor efficiency at each stage, and overall improve refrigeration cycle efficiency. is there.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the conventional example as described above, the discharge gas compressed to the intermediate pressure by the low-stage compressor is directly or indirectly with the high-pressure liquid refrigerant or the intermediate-pressure two-phase refrigerant. After being heat-exchanged and cooled, it is sucked into the high-stage compressor, compressed to a high pressure and discharged, so that two suction and discharge pipes are required to connect the compressor and the refrigeration cycle. The structure becomes complicated and causes vibration and noise of the compressor, or the device becomes very large. Further, in order to properly distribute the oil of the compressor to the low-stage side and the high-stage side, an oil separator, oil return, etc. are required, and parts other than the compressor are complicated.

The present invention provides a two-stage compression refrigeration cycle that can realize two-stage compression with a simple structure and can switch between one-stage compression and two-stage compression with a simple structure.

Means for Solving the Problems The two-stage compression refrigeration cycle of the present invention has at least a low-stage compression mechanism and a high-stage compression mechanism in a closed shell, and a discharge pipe of the low-stage compression mechanism is provided in the closed shell. The suction pipe of the low-stage side compression mechanism is configured by connecting the two-stage compressor with the suction pipe of the high-stage side compression mechanism opened in the closed shell to the condenser, expansion device, evaporator, etc. Is connected to the evaporator outlet, the discharge pipe of the high-stage compression mechanism is connected to the condenser inlet, and the pipe between the condenser outlet and the evaporator inlet and the closed shell are connected. .

Action With the above configuration, the refrigerant gas compressed and discharged by the low-stage compression mechanism is discharged into the closed shell. On the other hand, the refrigerant between the condenser outlet and the evaporator inlet of the refrigeration cycle is injected into the closed shell to cool the refrigerant discharged by the low-stage compression mechanism, and then the high-stage compression mechanism together with the low-stage discharge gas. Is sucked in, compressed and guided to the condenser inlet. By doing so, the intake gas temperature of the high-stage compressor can be lowered with a simple structure to prevent its discharge temperature from rising, and the compression ratio can be adjusted appropriately on the low-stage side and the high-stage side depending on the injection amount of the refrigerant. Since it can be set to, the compressor can be operated under the condition that the compressor efficiency of each stage is good, and the refrigeration cycle efficiency at a high compression ratio can be improved. Further, when the drive motor is arranged in the closed shell, the liquid refrigerant can be injected into the closed shell to be sufficiently cooled by its latent heat, so that the motor efficiency is improved, and the motor winding and the like are improved. It is not necessary to use a material with high heat resistance.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an embodiment of a two-stage compression refrigeration cycle of the present invention, in which 1 is a hermetic rotary compressor, 2 is a substantially cylindrical hermetic shell, and 3 is a motor attached to the upper portion of the hermetic shell 2. It is provided on the central axis of the closed shell 2.
Reference numerals 4 and 5 denote a low-stage compression mechanism and a high-stage compression mechanism, which are attached to the lower portion of the closed shell 2. Further, 6 is a suction pipe of the low-stage compression mechanism 4 (hereinafter, low-stage suction pipe), and 7 is a low suction pipe. The discharge pipe of the stage compression mechanism 4 (hereinafter low stage discharge pipe), 8 is the suction pipe of the high stage compression mechanism 5 (hereinafter high stage suction pipe), and 9 is the discharge pipe of the high stage compression mechanism 5 (hereinafter high stage). The low-stage discharge pipe 7 and the high-stage suction pipe 8 open in the closed shell 2 and communicate with each other. Further, 10 is a condenser, 11 is a throttling device, and 12 is an evaporator, which are connected to each other by piping, and connect the inlet of the condenser 10 and the high-stage discharge pipe 9 to each other, and the outlet of the evaporator 12 and the low-stage suction pipe 6 to each other. To form a refrigeration cycle. Further, the outlet of the condenser 10 and the upper part of the closed shell 2 are connected via a pressure reducing valve 13 and a pipe 14, and the outlet of the evaporator 12 and a pipe 14 are connected via a switching valve 15.

The operation method in such a configuration will be described.

First, the pressure ratio (compression ratio) between the low pressure and high pressure of the refrigeration cycle
If the value is large, operate with two-stage compression. In this case, the switching valve
15 closes. Here, a part of the liquid refrigerant at the outlet of the condenser 10 is decompressed by the decompression valve 13 to the intermediate pressure of the refrigeration cycle,
It is injected through the pipe 14 to the upper part in the closed shell 2. On the other hand, the low-pressure refrigerant gas flowing from the evaporator 12 into the low-stage suction pipe 6 is compressed by the low-stage compression mechanism 4 and discharged into the closed shell 2 through the low-stage discharge pipe 7. Also, the liquid refrigerant injected through the pipe 14 cools the motor by passing through a gap space of the motor, for example, a gap between the stator and the closed shell 2 or a gap between the stator and the rotor (not shown). In addition, the refrigerant gas discharged from the low-stage discharge pipe 7 is completely gasified while cooling, and is sucked into the high-stage suction pipe 8 together with the discharge gas on the low-stage side. Therefore, at this time, the inside pressure of the closed shell 2 is maintained at the intermediate pressure. Further, in the high-stage compression mechanism 5, the refrigerant gas is compressed from an intermediate pressure to a high pressure, goes out of the closed shell 2 through the high-stage discharge pipe 9 and flows into the condenser 10, and the expansion device 11, the evaporator 12 and the freezer. It circulates in the cycle and flows into the low-stage suction pipe 6 again. If the compression ratio is large here, the compression ratio on the low-stage side and the compression stage on the high-stage side can be reduced by performing such two-stage compression, so leakage and re-expansion in the compressor are reduced compared to single-stage compression. The volumetric efficiency is improved,
The rate of friction loss is also reduced and compressor efficiency is improved resulting in improved refrigeration cycle effectiveness. Further, by injecting the liquid refrigerant at the outlet of the condenser 10 into the closed shell 2, the motor can be sufficiently cooled by its latent heat, so that the motor efficiency is improved and the motor winding and the like are made of a material having high heat resistance. There is no need to set it, which is advantageous in design.

Next, the case of operating in single-stage compression will be described. In this case, the pressure reducing valve 13 is throttled to a substantially closed state and the switching valve 15 is opened so that the outlet of the evaporator 12 and the closed shell 2 communicate with each other. The refrigerant gas that has flowed in is not compressed by the low-stage compression mechanism 4 and is discharged into the closed shell 2 while maintaining a low pressure. Then, it is sucked into the high-stage suction pipe 8 as it is, compressed to a high pressure by the high-stage compression mechanism 5, and discharged to the high-stage discharge pipe 9. When the compression ratio is small as described above, in the two-stage compression operation, the compression ratio in each stage becomes too small, the proportion of mechanical loss increases, and the compressor efficiency decreases, so it is advantageous to operate in single-stage compression. It is possible to switch between one-stage compression and two-stage compression only by a simple operation of switching the switching valve 15, and it is possible to always select an appropriate operation method depending on the operating conditions of the refrigeration system, for example, the evaporation temperature. .

Next, a different embodiment of the present invention will be described with reference to FIG.
In FIG. 2, the parts having the same numbers as those in FIG. 1 have the same functions, and the description thereof will be omitted. Here, the outlet of the condenser 10 is a pressure reducing device, here a capillary tube.
It is connected to the three-way valve 17 via 16 and the inlet of the condenser 11 and the three-way valve 17
And the three-way valve 17 and the closed shell 2 by piping 14
Connected via the condenser 11 inlet and the closed shell 2,
Alternatively, the outlet of the capillary tube 16 and the closed shell 2 can be connected by switching the three-way valve 17. In the case of the two-stage compression at this time, the three-way valve 17 is set to the position shown. In this case, the liquid refrigerant at the outlet of the condenser 11 is throttled to an intermediate pressure by the capillary tube 16 and injected into the closed shell 2 through the three-way valve 17 and the pipe 14, and the operation is performed in the same manner as in FIG. Omit it. In the case of one-stage compression, a three-way valve
By rotating the 17 by 90 ° in the direction of the arrow, the inlet of the condenser 11 and the inside of the closed shell 2 are connected via the three-way valve 17 and the pipe 14, so that the inside of the closed shell 2 has a high pressure. Therefore, the refrigerant gas flowing into the low-stage suction pipe 6 is compressed to a high pressure by the low-stage compression mechanism 4 and discharged into the closed shell 2. And
It is not compressed in the high-stage compression mechanism 5, is discharged from the high-stage discharge pipe 9 as it is, flows into the condenser 10 and circulates in the refrigeration cycle. Also in this case, it is possible to switch between the one-stage compression and the two-stage compression only by a simple operation of switching the three-way valve 14, and it is possible to always select an appropriate operating method according to the operating conditions of the refrigeration system.

Although the outlet of the condenser 11 and the three-way valve 17 are connected by the capillary tube 16 here, it may be an expansion valve or the like, and a combination of an on-off valve instead of the three-way valve 17 or the like has the same effect. It is included in the invention.

Effects of the Invention As described above, the two-stage compression refrigeration cycle of the present invention can form a two-stage compression refrigeration cycle with a simple configuration.
This has the effect of reducing the weight and size of refrigeration equipment and the like.
Further, since the compression ratio can be appropriately set on the low stage side and the high stage side, the compressor efficiency can be improved and the refrigeration cycle efficiency can be improved. Further, when the drive motor is arranged in the closed shell, by jetting the liquid refrigerant into the closed shell, it can be sufficiently cooled by its latent heat, so that the motor efficiency is improved and the motor winding and the like are improved. It is also unnecessary to use a material having high heat resistance. Also, by connecting the evaporator outlet and the closed shell, or the condenser inlet and the closed shell via the switching valve, it is possible to easily switch between the first-stage compression and the second-stage compression depending on the size of the compression ratio only by the switching operation. The efficiency of the refrigeration cycle can be further improved according to the operating conditions.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a two-stage compression refrigeration cycle of one embodiment of the present invention, and FIG. 2 is a configuration diagram of a two-stage compression refrigeration cycle of a different embodiment of the present invention. 2 ... closed shell, 4 ... low-stage compression mechanism, 5 ... high-stage compression mechanism, 6 ... low-stage suction pipe, 7 ... low-stage discharge pipe, 8
…… High-stage suction pipe, 9 …… High-stage discharge pipe, 10 …… Condenser, 11
...... Throttle device, 12 …… Evaporator, 13 …… Reducing valve, 14 …… Piping, 15 …… Switching valve, 16 …… Capillary tube, 17 ……
… A three-way valve.

Claims (3)

[Claims] 1. A refrigeration cycle is configured by connecting at least a two-stage compressor, a condenser, a throttle device, and an evaporator, and a suction pipe of the low-stage compression mechanism is connected to the evaporator outlet. The discharge pipe of the high-stage compression mechanism is connected to the condenser inlet, the pipe between the condenser outlet and the evaporator inlet is connected to the closed shell, and the two-stage compressor is a closed shell. At least a low-stage side compression mechanism and a high-stage side compression mechanism, the discharge pipe of the low-stage side compression mechanism is opened in the hermetic shell, and the suction pipe of the high-stage side compression mechanism is in the hermetic shell. A two-stage compression refrigeration cycle, characterized in that it is configured to open in the. 2. A two-stage compression refrigeration cycle according to claim 1, wherein the evaporator outlet and the closed shell are connected via a switching valve. 3. The two-stage compression refrigeration cycle according to claim 1, wherein the condenser inlet and the closed shell are connected via a switching valve.