RU2743653C1 - Cascade refrigerating machine with compressor thermal stabilization system - Google Patents

Abstract

FIELD: refrigerating equipment.

SUBSTANCE: invention relates to refrigeration engineering and can be used for cooling objects or maintaining their low temperature by obtaining cold at low temperature level (below 120 °C). Compressor thermal stabilization system comprises serially installed solenoid valve of thermal stabilization line, controlled by programmable control unit, check valve of thermal stabilization line, throttling device of thermal stabilization line. Inlet to the solenoid valve of the thermal stabilization line is located after the supercooler subcooler of the lower branch of the cascade, and the output is connected to the compressor of the lower branch of the cascade.

EFFECT: technical result is stabilization of temperature mode of compressor of cascade cooler bottom stage lower branch at operation in transient modes and in temperature control in automatic mode without external additional cooling devices.

4 cl, 3 dwg

Description

The invention relates to refrigeration technology and can be used to cool objects or maintain their low temperature by obtaining cold at a low temperature level (below minus 120 ° C).

A cascade refrigeration machine is known from the existing prior art [RU Patent No. 2563049, published 09.20.2015], characterized in that it uses a liquid separator installed in series, dividing the refrigerant flow into gaseous and liquid components, a preliminary recuperative heat exchanger, a main recuperative heat exchanger, the main throttling device, evaporator, compressor and condenser, while the first outlet of the liquid separator is connected to the inlet of the direct refrigerant flow to the preliminary recuperative heat exchanger, and the second outlet of the liquid separator is connected through the preliminary throttling device to the return flow inlet to the preliminary recuperative heat exchanger, while the outlet of the refrigerant flow from condenser and the inlet to the liquid separator are interconnected by a heat exchanger, which is a subcooler condenser for the lower branch of the cascade and an evaporator for the upper branch of the cascade, which is a single-stage cooling a ding machine, in which a compressor, a condenser, a receiver, a throttling device, an evaporator are installed in series. In this case, the specified refrigeration machine will only work if it is used as a refrigerant in the lower branch of the cascade of a multicomponent mixture (at least two components). The normal boiling point of the components of the working mixture should lie in the temperature range from the ambient temperature to the required cooling temperature.

One of the advantages of this technical solution is the ability to achieve low temperatures (below minus 120 ° C) using commercially available single-stage compressors, instead of serially produced two-stage or not commercially available compressors with special crankcase cooling systems.

The disadvantage of this technical solution is that in the transient modes of operation of the cascade refrigeration machine (operation in the cooling down mode: from the moment the refrigeration machine is started until the specified temperature is reached) there is a significant increase in the compressor temperature of the lower branch of the cascade to a certain high level with its further decrease. The solution to this problem requires the use of additional technical means for external cooling of the compressor.

The dependence of the temperature change of the compressor of the lower stage in time during the operation of a real cascade refrigeration machine in transient modes of operation is as follows - Fig. one.

This form of the graph is explained by the fact that in the process of reaching a steady-state mode of operation, the cooling capacity of a cascade refrigeration machine is spent on compensating for changing heat inflows from the environment and cooling the heat-intensive mass of the case with objects of cooling, the heat transfer from which also changes over time.

As the heat-insulated casing with the objects of cooling cools down, the parameters of the phase equilibrium of the multicomponent mixture change, and the temperature of the flow at the suction to the compressor decreases, which ensures its effective cooling of the compressor with refrigerant vapors with a low temperature.

The maximum achievable value of the compressor temperature depends on a number of changing parameters, including the composition of the multicomponent mixture, the temperature of the suction and discharge flow, the mass flow rate of the working fluid, etc., which does not allow predicting the normal operation of the refrigeration machine, since the occurrence of overheating of the compressor of the lower stage is higher than the permissible level leads to its unstable operation, activation of the internal thermal protection devices of the compressor and a decrease in reliability indicators.

Also from the existing prior art, a system for regulating the composition of the refrigerant is known [RU Patent No. 2576561, published 03/10/2016], characterized in that it uses a receiver, from which the refrigerant is throttled to the suction of the compressor of the refrigeration machine due to the actuation of a solenoid valve, which in turn a programmable control unit controls a programmable control unit according to a given program, the input signals for which are a combination of the suction and discharge pressure signals of the compressor of the refrigeration machine, which significantly limits the operating time of the chiller at high discharge pressures (usually about 30 bar) and increases the reliability of the compressor and the chiller in the whole.

The disadvantage of this technical solution is that when operating in transient modes, it does not allow stabilizing the temperature regime of the compressor of the lower branch of the refrigerating machine cascade.

The technical result of the proposed technical solution is the stabilization of the temperature regime of the compressor of the lower branch of the cascade of a cascade refrigeration machine during operation in transient modes and during thermostating.

To achieve the specified technical result, in the claimed cascade refrigeration machine with a compressor thermal stabilization system, controlled bypass of cooled vapors of the refrigerant mixture after the subcooler condenser to the compressor suction of the lower branch of the cascade through a system of sequentially installed elements and refrigeration automation devices controlled by a programmable control unit (PBU ).

Thanks to these changes in the structure of the cycle, it is possible to stabilize the temperature regime of the compressor of the lower branch of the cascade and to ensure the uninterrupted operation of the cascade refrigeration machine in transient operating modes.

A schematic diagram of the developed cascade refrigeration machine with a compressor thermal stabilization system is shown in Fig. 2.

List of items shown in Figure 2:

pos. 1 - compressor of the lower branch of the cascade;

pos. 2 - oil separator;

pos. 3 - air condenser of the lower branch of the cascade;

pos. 4 - condenser - subcooler;

pos. 5 - liquid separator;

pos. 6 - preliminary recuperative heat exchanger;

pos. 7 - main recuperative heat exchanger;

pos. 8 - main throttling device;

pos. 9 - evaporator;

pos. 10 - preliminary throttling device;

pos. 11 - inlet solenoid valve;

pos. 12 - bypass receiver;

pos. 13 - output solenoid valve;

pos. 14 - check valve;

pos. 15 - additional throttling device;

pos. 16 - solenoid valve of the thermal stabilization line;

pos. 17 - check valve of the thermal stabilization line;

pos. 18 - throttling device of the thermal stabilization line;

pos. 19 - compressor of the upper branch of the cascade;

pos. 20 - air condenser of the upper branch of the cascade;

pos. 21 - receiver;

pos. 22 - throttling device of the upper branch of the cascade; item 23 - additional throttling device; PBU - programmable control unit; T - temperature sensor on the compressor housing.

A cascade refrigeration machine with a compressor thermal stabilization system consists of a circulation circuit of the upper branch of the cascade and a circulation circuit of the lower branch of the cascade. In the lower branch of the cascade, a liquid separator (pos. 5) is installed in series, separating the refrigerant flow into gaseous and liquid components, a preliminary recuperative heat exchanger (pos. 6), a main recuperative heat exchanger (pos. 7), a main throttling device (pos. 8), the evaporator (pos. 9), the compressor of the lower branch of the cascade (pos. 1), the oil separator (pos. 2) and the air condenser of the lower branch of the cascade (pos. 3), while the first outlet of the liquid separator (pos. 5) is connected to the inlet of the direct refrigerant flow into the pre-recuperative heat exchanger (pos. 6), and the second outlet of the liquid separator (pos. 5) is connected through a preliminary throttling device (pos. 10) with the return flow inlet to the pre-recuperative heat exchanger (pos. 6). The outlet of the refrigerant flow from the condenser (item 3) and the inlet to the liquid separator (item 5) are interconnected by a heat exchanger (item 4), which is a subcooler condenser for the lower branch of the cascade and an evaporator for the upper branch of the cascade, which is a single-stage refrigeration machine , in which the compressor of the upper branch of the cascade (pos. 19), the air condenser of the upper branch of the cascade (pos. 20), the receiver (pos. 21), the throttling device of the upper branch of the cascade (pos. 22), the condenser-subcooler (pos. four). In addition, the lower branch of the cascade is equipped with a bypass line containing in series installed inlet solenoid valve (item 11), bypass receiver (item 2), outlet solenoid valve (item 13), check valve (item 14), additional throttling device (item 15), while the inlet of the bypass line is located between the condenser of the lower branch of the cascade (item 3) and the subcooler-condenser of the lower branch of the cascade (item 4), and the outlet is between the compressor of the lower branch of the cascade (item 1) and the outlet from preliminary heat exchanger (pos. 6).

The compressor thermal stabilization system is a thermal stabilization bypass line that includes a thermal stabilization line solenoid valve (pos. 16) installed in series, a thermal stabilization line check valve (pos. 17) and a throttling device for the thermal stabilization line (pos. 18). In this case, the inlet to the bypass line of thermal stabilization is located between the condenser-subcooler of the lower branch of the cascade (pos. 4) and the liquid separator (pos. 5), and the outlet is between the compressor of the lower branch of the cascade (pos. 1) and the outlet from the preliminary heat exchanger (pos. 6).

The solenoid valves (pos. 11, 13, 16) are controlled by a programmable control unit (PBU) according to a given program, the input signals for which are a combination of signals from the suction pressure, discharge pressure and temperature "T" sensors on the compressor housing of the lower branch of the cascade ( pos. 1).

The refrigerating machine works as follows: in the lower branch of the cascade, the multicomponent refrigerant mixture is compressed in the compressor (pos. 1) and enters the oil separator (pos. 2), in which most of the lubricating oil is separated and returned to the compressor through an additional throttling device (pos. . 23). After that, the working fluid is cooled to ambient temperature, partially condensing in the air condenser of the lower branch of the cascade (item 3) and enters the condenser-subcooler (item 4), where the condensation process continues due to the low-potential heat obtained from the operation of the single-stage refrigeration machine of the upper branches of the cascade. Then the multicomponent refrigerant mixture enters the liquid separator (pos. 5), where it is separated into liquid and gaseous phases. The gaseous refrigerant from the liquid separator enters first the recuperative pre-heat exchanger (pos. 6), then into the main recuperative heat exchanger (pos. 7), where it is gradually condensed due to cooling by the reverse flow. The refrigerant cooled in this way passes through the main throttling device (pos. 8), where it expands and decreases in temperature, after which it enters the evaporator (pos. 9), where it is heated by the heat removed from the cooled objects. Then the refrigerant flow enters the main recuperative heat exchanger (item 7), where it is heated by cooling the direct flow. The liquid refrigerant from the liquid separator (pos. 5) passes through the pre-throttling device (pos. 10), where its pressure and temperature are reduced, after which it is mixed with the return flow upstream of the pre-recuperative heat exchanger (pos. 6). Further, the refrigerant flow is still heated in the preliminary recuperative heat exchanger (pos. 6) and enters the compressor suction (pos. 1). This closes the refrigeration machine cycle.

During the start-up period, the compressor (pos. 1) creates a vacuum in the low-temperature part of the cycle of the lower branch of the cascade - the evaporator (pos. 9), the main recuperative heat exchanger (pos. 7) and the preliminary recuperative heat exchanger (pos. 6), as a result of which the liquid phase of the multicomponent Mixed refrigerant, consisting of high-boiling components, evaporates, providing initial cooling and increasing the pressure at the compressor suction (item 1). As the volume of gaseous refrigerant in a constant volume system increases, the discharge pressure increases in the refrigeration circuit. Due to limitations on the discharge pressure for the compressor (item 1), the programmable control unit (PBU), at a certain discharge pressure value, gives a signal to open the inlet solenoid valve (item 11), thereby bypassing a portion into the bypass receiver (item 12) working medium of the refrigerating machine in the gaseous phase. In this case, the discharge pressure in the cycle decreases, the inlet solenoid valve (item 11) closes. Due to the high suction pressure during the start-up period in the lower branch of the cascade, the outlet solenoid valve (pos. 13) is in a closed state.

Thus, during the start-up period, a part of the multicomponent mixed refrigerant is withdrawn from the cycle, which ensures a decrease in the discharge pressure in the compressor and, accordingly, the discharge temperature. Due to this, in the initial period of time, it is possible to provide acceptable temperature conditions for the compressor (item 1).

As the boiling point decreases and the condensation of the intermediate components begins (changes in phase equilibrium) of the multicomponent mixed refrigerant, the suction and discharge pressures decrease over time and the PBU gives a signal to open the outlet solenoid valve (item 13) at the values of the suction and discharge pressures "simultaneously lower than optimal.

After opening the outlet solenoid valve (pos. 13), the refrigerant portion begins to throttle through the additional throttling device (pos. 15) from the bypass receiver (pos. 12) to the compressor suction (pos. 1), increasing the suction and discharge pressures to optimal values, after which closes the outlet flow solenoid valve (item 2).

Thus, due to periodic additions of portions of the multicomponent mixed refrigerant to the circuit of the lower branch of the cascade, the mass flow rate of the working fluid through the compressor (item 1) increases over time. This leads to an increase in its temperature with insufficient cooling by the vapors of the multicomponent mixed refrigerant at the suction due to their high temperature in transient modes due to the high heat transfer from the heat-intensive mass of the body and objects of cooling.

At the same time, upon reaching the set temperature on the compressor casing (pos. 1), measured by the "T" sensor, the thermal stabilization system begins to operate: the PBU gives a signal to open the solenoid valve of the thermal stabilization line (pos. 16), through which a portion of the multicomponent mixed refrigerant cooled in the condenser-pre-cooler (item 4), through the check valve of the thermal stabilization line (item 17) and the throttling device of the thermal stabilization line (item 18) enters the compressor suction line (item 1), mixing with the flow from the preliminary heat exchanger (item . 6).

Due to the inclusion of the thermal stabilization system, the temperature of the working fluid at the suction to the compressor (pos. 1) decreases, which ensures its cooling by refrigerant vapor with a low temperature.

As the heat-insulated casing with the objects of cooling cools down, the parameters of the phase equilibrium of the multicomponent refrigerant mixture change and the temperature of the working fluid at the compressor suction (item 1) decreases. At the same time, the temperature on the compressor casing (pos. 1), recorded by the "T" sensor, also decreases to the set one and the PBU gives a signal to close the solenoid valve of the thermal stabilization line (pos. 16). The thermal stabilization system stops its work, which ensures the circulation of the working fluid in full through the evaporator (pos. 9).

Thus, it is possible to organize staged cooling to ensure the optimal composition of the multicomponent working fluid in the evaporator of the refrigerating machine while maintaining acceptable temperature conditions for the compressor (item 1).

The duration of opening and closing of the inlet solenoid valve (pos. 11), the outlet solenoid valve (pos. 13), the solenoid valve of the thermal stabilization line (pos. 6), as well as the values of the setpoints - the optimal pressures and response temperatures, and their hysteresis are set depending on the standard size of the refrigeration machine operating according to the specified cycle, as well as depending on the qualitative and quantitative composition of the multicomponent mixture of refrigerants - the working fluid of the refrigeration machine.

Thanks to the use of the proposed cascade refrigeration machine with a compressor thermal stabilization system, it is possible to provide acceptable temperature conditions for the compressor (item 1) in automatic mode without external additional cooling devices. This makes it possible to use commercially available single-stage compressors in the specified scheme of a cascade refrigeration machine to obtain cold at low temperature levels (below minus 120 ° C).

FIG. 3, as an example of application, the dependence of the temperature change of the compressor of the lower branch of the cascade (item 1) and the air temperature in the working volume on time in the transient modes of operation of a real cascade refrigeration machine with a compressor thermal stabilization system is presented.

The standard sizes of the refrigerating machine elements and the settings of the control devices are selected in such a way as to ensure the compressor temperature in transient modes is not higher than 70 ° C and in the thermostatting mode when the refrigerating machine is running, not higher than 55C.

The proposed cascade refrigeration machine with a compressor thermal stabilization system is based on the use of equipment and devices that can be manufactured at domestic enterprises and / or commercially available components (compressors, heat exchangers, temperature and pressure sensors, programmable control units, etc.).

The proposed invention can be successfully applied to solving urgent problems of creating low-temperature refrigeration equipment for medicine, mechanical engineering and metalworking, etc.

Claims (4)

1. A cascade refrigeration machine with a compressor thermal stabilization system, containing in the lower branch of the cascade a liquid separator installed in series, dividing the refrigerant flow into gaseous and liquid components, a preliminary recuperative heat exchanger, a main recuperative heat exchanger, a main throttling device, an evaporator, a compressor of the lower branch of the cascade, an oil separator, air condenser of the lower branch of the cascade, a bypass line with inlet and outlet solenoid valves controlled by a programmable control unit, a bypass receiver, an additional throttling device, while the first outlet of the liquid separator is connected to the inlet of the direct refrigerant flow to the preliminary recuperative heat exchanger, and the second outlet of the liquid separator is connected through a preliminary throttling device with a return flow inlet to the preliminary recuperative heat exchanger, and the outlet of the refrigerant flow from the condenser and the inlet to the liquid separator and are interconnected by a heat exchanger, which is a condenser-subcooler for the lower branch of the cascade and an evaporator for the upper branch of the cascade, which is a single-stage refrigeration machine, in which the compressor of the upper branch of the cascade, an air condenser of the upper branch of the cascade, a receiver, a throttling device of the upper branch of the cascade, are installed in series, characterized in that it is equipped with a compressor thermal stabilization system, containing a series-installed solenoid valve of the thermal stabilization line controlled by a programmable control unit, a check valve for the thermal stabilization line, a throttling device for the thermal stabilization line, while the entrance to the solenoid valve of the thermal stabilization line is located after the condenser-supercooler of the lower branch of the cascade, and the outlet is connected to the compressor of the lower branch of the cascade. 2. A cascade refrigeration machine with a compressor thermal stabilization system according to claim 1, characterized in that the inlet of the bypass line with inlet and outlet solenoid valves controlled by a programmable control unit, a bypass receiver, an additional throttling device is located between the air condenser of the lower branch of the cascade and the subcooler condenser ... 3. A cascade refrigeration machine with a compressor thermal stabilization system according to claim 1, characterized in that the preliminary and main recuperative heat exchangers can be made as a single product with a preliminary throttling device connected between sections of the recuperative heat exchanger. 4. A cascade refrigeration machine with a compressor thermal stabilization system according to claim 1, characterized in that the air condenser of the upper branch of the cascade and the air condenser of the lower branch of the cascade can be made in a single casing and represent one multi-pass heat exchanger with one fan.

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