JPH08121889A - Refrigerating cycle - Google Patents

Abstract

PURPOSE: To prevent the deterioration in the refrigerant flow rate controllability of an expansion valve by introducing the flash gas of refrigerant to a low pressure side expansion valve in a refrigerating cycle for expanding by two stages according to high and low pressure side expansion valves. CONSTITUTION: A heat exchanger 6 for overcooling a saturated liquid refrigerant output from a vapor-liquid separator 4 is provided at a refrigerant tube 130 between the separator 4 provided at the outlet side of a high pressure side expansion valve 32 and a low pressure side expansion valve 31, and the overcooled refrigerant passed through the exchanger 6 is fed to the valve 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor compression refrigeration cycle, and is suitable as a cooling / heating device or a refrigeration device for an electric vehicle, for example.

[0002]

2. Description of the Related Art Conventionally, in a vapor compression refrigeration cycle consisting of a compressor, a condenser, an expansion valve, and an evaporator, it has a very low temperature such as a heat pump used as a heating device for an electric vehicle in winter and a freezer. When the object is cooled, the evaporation temperature of the refrigerant in the evaporator becomes low, the refrigerating effect is small, and the compression ratio is large, so that the work of compression is increased, so that the coefficient of performance (COP) becomes small.

Therefore, as a conventional method for improving the COP, the two-stage compression / two-stage expansion refrigeration cycle shown in FIGS. 7 and 8 and the economizer cycle shown in FIGS. 9 and 10 have been used. In the former two-stage compression / two-stage expansion refrigeration cycle, two compressors 11, 12 on the low-stage side (low-pressure side) and the high-stage side (high-pressure side) are arranged and discharged from the high-stage side compressor 12. The thus-refrigerated refrigerant releases heat and liquefies in the condenser 22, is depressurized to an intermediate pressure through the high-stage (high pressure side) expansion valve 32, and is sent to the gas-liquid separator 4.

In the gas-liquid separator 4, the discharge gas from the low-stage side (low-pressure side) compressor 11 flows in and mixes. At this time, a part of the liquid in the gas-liquid separator 4 is evaporated and the discharge gas of the low-stage compressor 11 is cooled to the saturation temperature. In the gas-liquid separator 4, the refrigerant is divided into saturated vapor and saturated liquid, and this saturated liquid is depressurized from the intermediate pressure to the evaporation pressure through the low-stage expansion valve 31 and sent to the evaporator 21. Further, the saturated vapor in the gas-liquid separator 4 is sucked into the high-pressure stage compressor 12 and compressed to a high pressure.

In this two-stage compression / two-stage expansion refrigeration cycle, the state of the refrigerant changes as shown in FIG.
Since the enthalpy difference in
The COP can be increased as compared with the stage compression cycle. On the other hand, in the latter economizer cycle, as shown in FIG. 9, the arrangement of the condenser 22, the evaporator 21, and the high-stage and low-stage expansion valves 31, 32 is the same as that of the two-stage compression two-stage expansion cycle, but The discharge port 111 of the side compressor 11 and the suction port 122 of the high-stage compressor are communicated with each other by a pipe 123, and a communication port 1 with the gas-liquid separator 4 is provided in the middle of the pipe 123.
24 are provided.

Therefore, the mixture of the refrigerant gas discharged from the low-stage side compressor 11 and the saturated vapor from the gas-liquid separator 4 is sucked into the high-stage side compressor 12 and compressed. Similar to the compression two-stage expansion cycle, the COP can be increased compared to the one-stage compression.

[0007]

By the way, in the above-mentioned two-stage compression / two-stage expansion refrigeration cycle and economizer cycle, the liquid refrigerant saturated in the gas-liquid separator 4 is brought to an intermediate pressure by the low-stage expansion valve 31. However, since the refrigerant pressure decreases due to the pressure loss of the refrigerant pipe 130 between the gas-liquid separator 4 and the low-stage expansion valve 31, flash vapor is generated in the saturated liquid refrigerant. There is.

The flash steam intermittently and unstablely flows into the throttle passage of the low-stage expansion valve 31, and the flow resistance between the gas and the liquid changes significantly, so that the expansion valve 31
The controllability of the refrigerant flow rate deteriorates. Specifically, the expansion valve 3
1 causes a problem such as hunting. The present invention is to solve such a problem, and suppresses the generation of flash vapor by precooling the refrigerant flowing into the low pressure side expansion valve in advance, and improves the refrigerant flow rate controllability of the low pressure side expansion valve. The object is to provide a refrigeration cycle that can be performed.

[0009]

In order to achieve the above object, the present invention provides a gas-liquid separator in a refrigeration cycle having a two-stage expansion process such as the above-mentioned two-stage compression / two-stage expansion refrigeration cycle or economizer cycle. The refrigerant pipe (130) between (4) and the low pressure side expansion valve (31) is provided with a heat exchanger (6) for cooling the refrigerant.

That is, according to the first aspect of the invention, the compressor (11, 12), the condenser (22), the expansion means (32,
31), in the vapor compression refrigeration cycle including the evaporator (21), the expansion process is performed in two stages by the high pressure side expansion means (32) and the low pressure side expansion valve (31),
A refrigeration cycle in which a gas-liquid separator (4) for separating a saturated vapor and a saturated liquid of a refrigerant is provided between the high-pressure side expansion means (32) and the low-pressure side expansion valve (31). The refrigeration cycle is characterized in that the heat exchanger (6) for cooling the refrigerant is provided in the refrigerant pipe (130) between the device (4) and the low pressure side expansion valve (31).

According to a second aspect of the invention, in the refrigeration cycle of the first aspect, the heat exchanger (6) is joined to the refrigerant pipe (130) and is cooled by the outside air. It is characterized by being constituted by. According to a third aspect of the present invention, in the refrigeration cycle according to the first aspect, the heat exchanger (6) is a part of the refrigerant pipe (130) that is in contact with or joined to the evaporator (21) ( 57) is provided.

According to a fourth aspect of the present invention, the refrigerating cycle according to the first aspect is used in an automobile air conditioner, and the heat exchanger (6) is an outside air introducing duct (6) of the automobile air conditioner.
6) It is characterized by a refrigeration cycle installed inside. The reference numerals in parentheses of the above means indicate the corresponding relationship with the specific means described in the embodiments described later.

[0013]

According to the inventions of claims 1 to 4,
Since it has the above technical means, the refrigerant from the gas-liquid separator to the low-pressure side expansion valve is cooled by the heat exchanger arranged in the refrigerant pipe between the gas-liquid separator and the low-pressure side expansion valve, The enthalpy decreases by δH in FIG. 3 (b). On the other hand, due to the pressure loss in the refrigerant pipe, the refrigerant pressure between the gas-liquid separator and the low-pressure side expansion valve decreases by δP in FIG.
Since the refrigerant is supercooled by δH by the heat exchanger, the refrigerant reaching the low pressure side expansion valve remains in a liquid state, and the generation of flash vapor can be suppressed.

As a result, problems such as hunting of the low pressure side expansion valve due to the inflow of flash vapor can be prevented, and the refrigerant flow rate controllability of the expansion valve can be improved.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows a first embodiment of the present invention in which the refrigeration cycle has a low-stage compressor 11 and a high-stage compressor 1.
2, condenser 22, evaporator 21, high-stage side (high-pressure side) expansion valve 32, low-stage side (low-pressure side) expansion valve 31, gas-liquid separator 4, and this gas-liquid separator 4 and low-stage expansion The heat exchanger 6 for cooling the refrigerant is arranged in the refrigerant pipe 130 between the valves 31. The low-stage expansion valve 31 is a temperature-operated expansion valve that controls the refrigerant superheat degree at the outlet of the evaporator 21 to a predetermined value, and may be either an external equalization type or an internal equalization type. Further, as the low-stage side expansion valve 31, it is possible to use an electric expansion valve that electrically controls the valve opening degree.

In the heat exchanger 6, as shown in FIG. 2, a plurality of plate-like fins 42 made of copper or aluminum having good heat conduction are joined to the refrigerant pipe 130 made of the same kind of metal by brazing or welding. It is formed by joining by means.
As a place to install the heat exchanger 6, a place where the plate fin 42 is easily cooled by the outside air is preferable. In the case of a refrigeration cycle device for automobiles, the heat exchanger 6 is installed at a place where air is blown by the ram pressure generated by traveling of the automobile.
It is preferable to enhance the cooling effect of the heat exchanger 6.

The operation of the above structure will be described. The saturated gas refrigerant in the gas-liquid separator 4 is mixed with the gas refrigerant discharged from the low-stage compressor 11 and then sucked and compressed by the high-stage compressor 12. The condenser 22 radiates heat and liquefies. After that, the liquefied refrigerant reaches the gas-liquid separator 4 through the high-stage expansion valve 32, and is separated into a saturated liquid refrigerant and a saturated gas refrigerant there.

The liquid refrigerant in the gas-liquid separator 4 is pipe 1
After passing through the heat exchanger 6 through 30, the enthalpy is reduced by δH as shown in FIG. 3 (b), and then the pressure is reduced by the low stage expansion valve 31 and vaporized by the evaporator 21, and then the low stage side. It is sucked into the compressor 11. FIG. 3 is a Mollier diagram of the first embodiment, and FIG. 3B is an enlarged view of the x portion of FIG.
If there is no heat exchanger 6, the pressure loss δP of the refrigerant pipe 130
Since the pressure decreases only, the refrigerant at the point A, that is, the refrigerant in the gas-liquid coexisting state flows into the low-stage expansion valve 31. But,
When the heat exchanger 6 cools the refrigerant to reduce the enthalpy by δH, the supercooled refrigerant at the point B flows in, and the generation of flash vapor of the refrigerant can be suppressed.

For example, when the enthalpy of the refrigerant is reduced by δH = 0.42 kcal / Kg in the heat exchanger 6 when the intermediate pressure in the gas-liquid separator 4 is 5 kgf / cm ² , the pressure loss δP in the refrigerant pipe 130. Is 0.2 kgf
If it is / cm ² or less, flash steam is not generated at the inlet of the low-stage expansion valve 31. Therefore, hunting of the low-stage expansion valve 31 due to the flash steam does not occur, and the controllability of the refrigerant flow rate is maintained in a good state. (Second Embodiment) FIG. 4 shows a second embodiment of the heat exchanger 6 of the present invention, in which a part of the refrigerant pipe 130 extending from the gas-liquid separator 4 to the low-stage expansion valve 31 is provided with an evaporator 21. The portion 57 that is in contact with or joined to the pipe or fin is provided, and the refrigerant pipe 130
By cooling the refrigerant passing through it by the evaporator 21, which has a lower temperature, the enthalpy is reduced and the generation of flash vapor is suppressed.

According to this example, since the heat exchange in the heat exchanger 6 is performed between the portion 57 of the refrigerant pipe 130 and the evaporator 21, the coefficient of performance of the refrigeration cycle does not change and the evaporator 2 does not change.
It does not affect the performance of 1. (Third Embodiment) FIG. 5 shows a third embodiment, which is an example of a heat pump of an air conditioner for an electric vehicle. When heating the passenger compartment in the winter, in the inside air circulation mode in which the passenger compartment air is circulated, the humidity inside the passenger compartment increases due to water vapor generated from the human body of the occupant, and the visibility deteriorates because of condensation on the inner surface of the glass window. It is very dangerous when driving a car.

In order to prevent this, a device has been proposed which suppresses an increase in humidity by introducing a part of outside air into the inside air as the introduction air of the air conditioner. Therefore, in the third embodiment, in the air conditioner having such a configuration, the outside air introduction duct 6
A heat exchanger 6 disposed between the gas-liquid separator 4 and the low stage side expansion valve 31 is provided inside the suction port or the duct of 6. Since the refrigerant passing through the heat exchanger 6 is forcibly cooled by the outside air introduced into the vehicle interior 64 by the outside air introduction fan 63,
The enthalpy is reduced and it becomes a supercooled state, and the generation of flash vapor can be suppressed.

In FIG. 5, reference numeral 62 designates an internal air circulation fan,
Reference numeral 64 is a vehicle compartment, and 65 is an inside air circulation passage. A Mollier diagram of the third embodiment is shown in FIG. Between the gas-liquid separator 4 and the low-stage expansion valve 31, the refrigerant is supercooled by the heat exchanger 6 by the amount of enthalpy δH. At this time, since the outside air introduced into the vehicle compartment is heated by the heat exchanger 6, the heating effect in the vehicle compartment is improved. On the other hand, since the compression work has nothing to do with the presence or absence of the heat exchanger 6, the compression work does not change.

From the above, in the third embodiment, not only the effect of suppressing flash vapor generation in the low stage expansion valve 31 but also the effect of improving the COP calculated by the heating effect / compression work can be expected. It should be noted that the refrigeration cycle does not have to be composed of two compressors, and a compound compressor capable of performing multi-stage compression with one compressor, or introducing gas into the compression chamber during the compression process of the compressor has the same effect as the two-stage compression. You may use the compressor which obtains.

Further, the high-pressure side expansion means is not limited to the expansion valve 32, and it is also possible to use a fixed throttle such as a capillary tube or an orifice. Also,
The heat exchanger 6 may be configured to cool the refrigerant by using the low temperature condensed water generated in the evaporator 21.

[Brief description of drawings]

FIG. 1 is a refrigeration cycle diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a perspective view showing the configuration of the heat exchanger according to the first embodiment of the present invention.

FIG. 3A is a Mollier diagram of the first embodiment of the present invention,
(B) is an enlarged view of part x of (a).

FIG. 4 is a schematic diagram showing a configuration of a heat exchanger according to a second embodiment of the present invention.

FIG. 5 is a schematic configuration diagram showing a third embodiment of the present invention.

FIG. 6 is a Mollier diagram of the third embodiment of the present invention.

FIG. 7 is a refrigeration cycle diagram showing a configuration of a conventional two-stage compression two-stage expansion cycle.

8 is a Mollier diagram for the cycle of FIG. 7.

FIG. 9 is a refrigeration cycle diagram showing a configuration of a conventional economizer cycle.

10 is a Mollier diagram for the cycle of FIG.

[Explanation of symbols]

11 ... Low-stage compressor, 12 ... High-stage compressor, 21 ...
… Evaporator, 22 …… Condenser, 31 …… Low pressure side expansion valve, 3
2 ... High-pressure side expansion valve, 130 ... Refrigerant piping, 4 ... Gas-liquid separator, 6 ... Heat exchanger.

Claims (4)

[Claims] 1. A vapor compression refrigeration cycle comprising a compressor, a condenser, an expansion means and an evaporator, wherein the expansion process is performed in two stages by a high pressure side expansion means and a low pressure side expansion valve, and the high pressure A refrigeration cycle provided with a gas-liquid separator for separating a saturated vapor and a saturated liquid of a refrigerant between the side expansion means and the low-pressure side expansion valve, wherein the gas-liquid separator and the low-pressure side expansion valve A refrigeration cycle characterized in that a heat exchanger for cooling the refrigerant is provided in the refrigerant pipe. 2. The refrigeration cycle according to claim 1, wherein the heat exchanger is constituted by a fin member joined to the refrigerant pipe and cooled by outside air. 3. The refrigeration cycle according to claim 1, wherein the heat exchanger is configured by providing a part of the refrigerant pipe which is in contact with or joined to the evaporator. 4. A refrigeration cycle according to claim 1, wherein the refrigeration cycle is used in an automobile air conditioner, and the heat exchanger is installed in an outside air introduction duct of the automobile air conditioner.