JPH0321824B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cascade type refrigeration system that can prevent a pressure rise in the system at the time of startup while obtaining a necessary low temperature.

A refrigeration system for obtaining low temperatures that uses a single-stage compressor to circulate refrigerant in a cascade type refrigeration circuit is known from U.S. Patent No. 2041725, and a typical refrigeration circuit is As shown in Figure 4, the non-azeotropic mixed refrigerant gas discharged from the compressor 1 is condensed in a condenser 2, and then separated into a high temperature side refrigerant liquid and a low temperature side refrigerant gas in a gas-liquid separator 3. The high temperature side refrigerant liquid is sent to the cooling side passage of the cascade condenser 4 after being depressurized by the high temperature side expansion valve 8, while the low temperature side refrigerant gas is depressurized by the low temperature side expansion valve 7 through the cooled side passage of the cascade condenser 4. The refrigerant circulation operation is completed in which the refrigerant is evaporated in the cooler (or evaporator) 5 and then sent to the cooling side passage of the cascade condenser 4, and the non-azeotropic mixed refrigerant mixed in this cooling side passage is sucked into the compressor 1. It is something that will be done.

In this type of mixed refrigerant cascade type refrigeration system, increasing the mixing ratio of low-temperature side refrigerants R13, R14, etc. is an effective means to obtain a low temperature. The disadvantage was that the pressure rose to such a high level that it could not be used in practice, especially at startup.

This point will be further explained below. In other words, among the refrigerants accumulated in the circuit at startup, the easily vaporized low-temperature refrigerant (high-pressure refrigerant) evaporates first, and when the system is stopped, the low-temperature refrigerant enters the gas phase in the system. Immediately after startup, a mixed refrigerant with a high content of low-temperature refrigerant circulates in the system, and due to the characteristics of low-temperature refrigerant, the discharge pressure of compressor 1 increases. As a result, there are cases where it becomes impossible to actually use it.

Furthermore, when the refrigerant starts flowing into the circuit, the high-temperature refrigerant and the low-temperature refrigerant begin to flow simultaneously, and the high-temperature refrigerant is sufficient to condense and liquefy the low-temperature refrigerant gas that flows into the cascade condenser 4 in a gaseous state. Immediately after startup, there is not much flow, so the compressor discharge pressure increases, albeit for a short time.

For the reasons mentioned above, the compressor discharge pressure increases to an extent that it cannot be used in practice at startup.

In this way, in view of the fact that although the conventional cascade type refrigeration equipment aims to obtain the necessary low temperature by increasing the mixing ratio of the low-temperature side refrigerant, the discharge pressure rises abnormally at startup, making it difficult to put it into practical use. During steady operation, the low-temperature refrigerant flows through the system to exhibit the characteristics of the low-temperature refrigerant without overloading the compressor, and at startup, it takes advantage of the advantages of the cascade refrigeration cycle to reduce the amount of refrigerant in the mixed refrigerant. The object of this invention is to provide a refrigeration system that can suppress pressure rise through the flow of high-temperature side refrigerant, and is capable of achieving both smooth startup and improved low-temperature characteristics.

Therefore, the present invention particularly relates to this type of cascade type refrigeration system, in which the liquid phase part of the gas-liquid separator 3 for separating high-temperature side refrigerant liquid and low-temperature side refrigerant gas is connected to the inlet of high-temperature side expansion valve 8. A check valve 1 that allows refrigerant to flow only to the high temperature side expansion valve 8 side in the liquid pipe line.
1. The liquid receiver 6 and the first on-off valve 10 are interposed in series from the upstream side, and the cascade condenser 4
A second on-off valve 9 is interposed in the liquid pipe connecting the cooled side passage and the inlet of the low-temperature side expansion valve 7, and the suction pressure of the compressor 1 is detected to prevent the compressor 1 from being overloaded. A pressure detector 12 that transmits a low pressure signal when the pressure is lower than a set value corresponding to an allowable pressure, and a pressure detector 12 that detects the temperature of the refrigerant in the cooled side passage in the cascade condenser 4 when it is lower than a predetermined set value. a temperature sensor 13 that transmits a low temperature signal when the low pressure signal is transmitted, and the first on-off valve 10 is opened only when the low pressure signal is transmitted and the low temperature signal is not transmitted, and when the low temperature signal is transmitted, the first on-off valve 10 is opened; Only, the control circuit for opening the second on-off valve 9 is connected to the operation section of the first and second on-off valves, and at the time of startup, the low temperature that affects the pressure rise is maintained. Since the refrigerant is limited to what accumulates in the cooling side passage of the cooler and cascade condenser, the pressure rise immediately after startup can be suppressed to a small level.On the other hand, during steady operation after startup is completed, the high temperature side refrigerant is By retaining the refrigerant in the liquid receiving pipe, the circulating refrigerant can be used as a low-temperature refrigerant, resulting in good low-temperature characteristics, and the intended purpose has been fully achieved.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

1 to 3 are device circuit diagrams showing one example of the device of the present invention according to the operating mode, including a compressor 1, a condenser 2, a gas-liquid separator 3, a cascade condenser 4, a cooler (or It is equipped with a cascade-type refrigeration circuit consisting of an evaporator) 5, a low-temperature side expansion valve 7, and a high-temperature side expansion valve 8.Since this refrigeration circuit is equivalent to the conventional device shown in Fig. 4, detailed explanation will be given here. Omitted.

In this cascade type refrigeration system, a check valve that allows refrigerant to flow only to the high temperature side expansion valve 8 side is provided in the liquid pipeline connecting the liquid phase part of the gas-liquid separator 3 and the inlet of the high temperature side expansion valve 8. 11. Three members, a liquid receiver 6, a first on-off valve, for example, a solenoid valve 10, are interposed in series from the upstream side in the order listed, and also a cooled side passage of the cascade condenser 4 and a low temperature side expansion valve. A second on-off valve, such as a solenoid valve 9, is interposed in the liquid pipe line that communicates with the liquid pipe 7.

12 is a pressure that is branch-connected to the suction pipe connected to the suction port of the compressor 1, detects the suction pressure, and sends a low pressure signal when the suction pressure is lower than a set value corresponding to the allowable pressure that does not overload the compressor 1; 13 is a temperature sensor having a temperature sensing section attached to a liquid pipe line connected to the inlet of the second electromagnetic valve 9, and is a temperature sensor 13 which is a temperature sensor in which a temperature sensing part is attached to a liquid pipe line connected to the inlet of the second solenoid valve 9, The temperature of the sensor is detected and a low temperature signal is sent when the temperature is lower than a predetermined set value.

The refrigeration system having the circuit configuration described above has a control circuit connected to the operating sections of the first and second solenoid valves 10 and 9.

Although this control circuit is not shown, the first electromagnetic valve is opened only when the low pressure signal is transmitted from the pressure sensor 12 and the low temperature signal from the temperature sensor 13 is not transmitted. Only when the low temperature signal is being transmitted, the second on-off valve 9
A control circuit for opening the valve is formed, and the circuit is connected to the operation section of the re-electromagnetic valves 10 and 9.

The above-mentioned refrigeration system is operated as follows.

That is, when starting the device (starting the fans for the compressor 1 and condenser 2 and the fan for the cooler 5), the first solenoid valve 10 and the second solenoid valve 9 are activated.
Leave it in the closed state.

In this state, part of the refrigerant gas that has exited the compressor 1 is liquefied in the condenser 2, separated into high-temperature side refrigerant liquid and low-temperature side refrigerant gas in the gas-liquid separator 3, and the refrigerant liquid is separated from the check valve 11. The refrigerant gas is accumulated in the liquid receiver 6 and in the cooled side passage of the cascade condenser 4, respectively.

On the other hand, since the first solenoid valve 10 and the second solenoid valve 9 are closed, the refrigerant gas accumulated in the cooling side passage of the cascade condenser 4 and the cooler 5 is stored on the suction side of the compressor 1. Therefore, the effect of low-temperature refrigerant at the time of startup is that the amount of gas sucked is limited, so immediately after startup, the pressure rise is suppressed to a small level, which puts a high burden on the compressor. It is possible to avoid this.

This operating state is as shown in FIG. 1, and when the suction pressure becomes sufficiently low and the compressor 1 is no longer overloaded, the pressure detector 12 detects a pressure lower than the set value. When the temperature rises, a signal is issued to operate the control circuit, and the first solenoid valve 10
to open. At this time, the temperature of the refrigerant in the cooled side passage in the cascade condenser 4 is determined by the temperature sensor 13.
is higher than the predetermined set value and no low temperature signal is being transmitted.

Thus, as shown in FIG.
The refrigerant passes through the first electromagnetic valve 10 and reaches the high temperature expansion valve 8, and after being depressurized, it exchanges heat with the low temperature side refrigerant gas also present in the cooled side passage in the cooling side passage of the cascade condenser 4, and then evaporates.

On the other hand, the low pressure side refrigerant gas is condensed and liquefied. Thereby, it is possible to cool the low temperature side refrigerant, which is the main cause of increasing the pressure in the circuit, and to lower the pressure.

Compressor 1 continues to maintain suction pressure low.
is operated, the low-temperature side refrigerant accumulated in the cooled side passage of the cascade condenser 4 is sufficiently condensed and liquefied, and a temperature detector detects that the refrigerant in the cooled side passage has been cooled compared to a predetermined temperature setting value. The control circuit is operated only when the low-temperature signal detected by the controller 13 is being transmitted, and the second solenoid valve 9 is opened and the first solenoid valve 10 is closed.

In this way, steady operation is achieved as shown in Figure 3.
By continuing this operation with the first solenoid valve 10 closed, most of the high temperature side refrigerant liquid separated by the gas-liquid separator 3 is stored in the liquid receiver 6, and the refrigerant circulating in the circuit is All or most of the amount becomes the low-temperature side refrigerant.

At this time, the low-temperature side refrigerant is liquefied and supercooled, passes through the low-temperature side expansion valve 7, and is partially evaporated in the cooler 5, thereby cooling the air.

In addition, a portion of the unevaporated part flows into the cooling side passage of the cascade condenser 4 and evaporates, cooling the low temperature side refrigerant and liquefying it, turning it into superheated gas and being sucked into the compressor 1.

Thus, substantially only the low-temperature refrigerant circulates within the circuit, and the characteristics of the low-temperature refrigerant are well exhibited.

The present invention has the configuration and operation as described above, and during steady operation after startup, the solenoid valve 10 is closed and the high-temperature side refrigerant is stored in the liquid receiver 6 to reduce the system pressure. This has the effect of increasing the circulation rate of the low-temperature side refrigerant without raising the temperature, thereby exhibiting the characteristics of the low-temperature refrigerant, and improving the low-temperature characteristics of the refrigeration system.

Furthermore, at startup, among the refrigerants stored in each system, the low-temperature side refrigerant (high-pressure refrigerant) stored in the cascade condenser 4 and cooler 5 is sucked in and discharged first, increasing the system pressure. is gone,
This also has the effect of reducing the load on the compressor 1, making it easier to start up, and increasing safety.

[Brief explanation of the drawing]

1 to 3 are device circuit diagrams showing examples of the present invention according to operating modes, and FIG. 4 is a conventional refrigeration device circuit diagram. 1... Compressor, 2... Condenser, 3... Gas-liquid separator, 4... Cascade condenser, 5... Cooler, 6
...Liquid receiver, 7...Low temperature side expansion valve, 8...High temperature side expansion valve, 9...Second on-off valve, 10...First on-off valve, 11...Check valve, 12...Pressure detection vessel, 13
...Temperature detector.

Claims (1)

[Claims] 1 The non-azeotropic mixed refrigerant gas discharged from the compressor 1 is condensed in the condenser 2, and then separated into high temperature side refrigerant liquid and low temperature side refrigerant gas in the gas-liquid separator 3, and the high temperature side refrigerant liquid is separated into high temperature side refrigerant gas. Through expansion valve 8, cascade condenser 4
while sending the low temperature side refrigerant gas to the cooling side passage of the cascade condenser 4 through the cooled side passage of the cascade condenser 4, the low temperature side expansion valve 7, and the cooler 5 in order, In a cascade type refrigeration system in which the non-azeotropic mixed refrigerant gas in the cooling side passage is sucked into the compressor 1, in the liquid pipe line connecting the liquid phase part of the gas-liquid separator 3 and the inlet of the high temperature side expansion valve 8. In addition, a check valve 11 that allows refrigerant to flow only to the high temperature side expansion valve 8 side, a liquid receiver 6, and a first on-off valve 10 are interposed in series from the upstream side, and the cascade condenser 4 is cooled. A second on-off valve 9 is interposed in the liquid pipe connecting the side passage and the inlet of the low-temperature side expansion valve 7, and the suction pressure of the compressor 1 is detected to establish an allowable pressure that does not overload the compressor 1. A pressure sensor 12 that detects the temperature of the refrigerant in the cooled side passage in the cascade condenser 4 and generates a low temperature signal when the temperature is lower than a predetermined set value. Temperature detector 13 that transmits
and only when the low pressure signal is transmitted and the low temperature signal is not transmitted, the first on-off valve 10
A control circuit for opening the second on-off valve 9 only when the low temperature signal is being transmitted is connected to the operating section of the first and second on-off valves 10 and 9. A cascade type refrigeration system featuring: