RU2576561C1 - Control system of the coolant composition - Google Patents

Abstract

FIELD: manufacturing technology.

SUBSTANCE: invention relates to refrigerating equipment, is intended for use in low-temperature vapour compression refrigerating machines operating on multi-component mixtures of cooling agents, for controlling composition of cooling agent fed into evaporator. Control system for cooling agent composition containing liquid separator located after condenser, and bypass line with in-series located bypass solenoid valve, receiver and throttling device. Cooling agent from the bypass line is directed immediately on to suction in compressor, the coolant supply from bypass line to suction in compressor is controlled by an additional solenoid valve located between receiver and throttling device of bypass line controlled by programmable control unit with preset program.

EFFECT: invention allows improving thermodynamic efficiency of vapour compression cooling machine operating on multi-component mixture of coolants.

2 cl, 1 dwg

Description

The invention relates to refrigeration, is intended for use in low-temperature vapor compression refrigeration machines operating on multicomponent mixtures of refrigerants, to control the composition of the refrigerant entering the evaporator.

To obtain low temperatures (from minus 40 ° C to minus 160 ° C), vapor compression refrigeration machines operating on multicomponent mixtures of refrigerants with an adjustable main throttling device are widely used. One of the main technical problems associated with the use of such chillers is that in the process of reaching a mode that can last up to several days, a mixture of uncontrolled uncontrolled refrigerant composition is circulated in the evaporator, as a result of which the chiller starts to work in the evaporator a significant amount of low-boiling components of the mixed refrigerant comes in, which are in a gaseous state at high current cooling temperatures: they do not condense and do not evaporate . The ballast gaseous stream of low-boiling refrigerant through the evaporator leads to a decrease in the isothermal choke effect in the low-temperature cycle. In this regard, the time required for the chiller to reach the mode and, accordingly, the energy consumed for this increase.

The solution to this problem is the proposed system for regulating the composition of the refrigerant, which allows you to automatically adjust the composition of the refrigerant circulating in the evaporator in the process of entering the mode of a vapor compression refrigeration machine operating on a multicomponent mixture of refrigerants with an adjustable main throttling device.

Known refrigeration machine (RU 2448308 C1, IPC F25B 1/00, 2006.01), in which the composition of the mixed refrigerant entering the evaporator is regulated. The specified refrigeration machine is used in low-temperature vapor compression refrigeration machines, runs on a multicomponent mixture of refrigerants and is designed to produce low temperatures. In this refrigeration machine, the refrigerant is compressed in the compressor, then cooled to ambient temperature and partially condensed in the condenser, after which it enters the liquid separator, where it is separated into liquid and gaseous phases. The gaseous refrigerant from the liquid separator enters first into the preliminary recuperative heat exchanger, and then into the main recuperative heat exchanger, where it gradually condenses due to cooling by the return flow. The cooled refrigerant passes through the main throttling device, where it expands and the temperature drops, and then enters the evaporator, where it is heated by heat removed from the cooled object. Further, the flow of refrigerant enters the main recuperative heat exchanger, where it is heated by cooling the direct flow. Liquid refrigerant from the liquid separator passes through a pre-throttling device, where its pressure and temperature are lowered, and then mixed with the return flow before the preliminary recuperative heat exchanger. Further, the refrigerant stream is still heated in the preliminary recuperative heat exchanger and is supplied to the compressor suction. At this, the cycle of the chiller is closed. The solenoid valve of this chiller, located in front of the receiver, is normally in the closed position and opens using an electrical signal from the control device. If the discharge pressure rises above a predetermined value, the solenoid valve opens and bypasses part of the gaseous stream of refrigerant into the receiver. The solenoid valve closes as soon as the pressure drops to the set value. From the receiver, the refrigerant passes through a check valve and a throttling device, where its pressure drops to the pressure of the return flow, and the temperature drops and mixes with the return flow before the preliminary recuperative heat exchanger. Based on the design, RU 2448308 does not eliminate the above technical problem, because has the following disadvantages:

- during the start-up period in this chiller, a significant part of the high-boiling components of the mixed refrigerant will be bypassed to the receiver by the solenoid valve due to the multiple increase in the discharge pressure above the pressure limit set for the compressor, which will lead to loss of cooling capacity at high boiling points in the evaporator;

- in this chiller at the initial moment of time at high boiling points in the evaporator, a significant part of the low-boiling refrigerant in the mixture, which is in the cycle only in the gaseous state, enters the evaporator between the moments of transfer to the receiver due to the continuous throttling of the refrigerant from the receiver to the suction, which leads to reduction of the isothermal throttle effect;

- due to the continuous transfer of refrigerant to the suction from the receiver, it is not possible to strictly control the boiling point in the evaporator.

The technical result of the invention is a significant reduction in the time the chiller enters the mode, which leads to a reduction in energy consumption. Also, by using the proposed refrigerant composition control system, the thermodynamic efficiency of the vapor compression refrigeration machine operating on a multicomponent mixture of refrigerants is increased.

To achieve a technical result, it is necessary to solve the problem of ensuring the optimal composition of multicomponent refrigerant in the evaporator in the process of reaching the operating mode in vapor compression refrigerating machines operating on multicomponent mixtures of refrigerants.

The drawing shows a diagram of a vapor compression refrigeration machine operating on a multicomponent mixture of refrigerants, in this diagram, a system for controlling the composition of the refrigerant is highlighted.

The list of elements indicated in the drawing:

1 - receiver;

2 - solenoid valve;

3 - throttling device;

4 - suction pressure sensor in the compressor;

5 - compressor discharge pressure sensor;

6 - programmable control unit;

7 - compressor of the refrigeration machine;

8 - capacitor;

9 - bypass solenoid valve;

10 - liquid separator;

11 - preliminary throttling device;

12 - recuperative heat exchanger;

13 - the main throttling device;

14 - evaporator;

P2 - compressor discharge pressure

p1 - suction pressure to the compressor

The refrigerant composition control system consists of a receiver 1, which is a container connected to the bypass solenoid valve 9 and the compressor suction line 7 by means of an uncontrolled throttling device 3 and a solenoid valve 2, which allows adding mixed refrigerant enriched in low-boiling mixture components to the circuit. The solenoid valve 2 is controlled by a programmable control unit 6, the input signals for which are: the suction pressure to the compressor "p1", measured by the suction pressure sensor 4, and the discharge pressure of the compressor "p2", measured by the discharge pressure sensor 5.

In the start-up period, the compressor 7 creates a vacuum in the low-temperature part of the cycle — the evaporator 14 and the recuperative heat exchanger 12, as a result of which the liquid refrigerant located there, which is the high-boiling components of the working medium of the refrigeration machine — a multicomponent mixture of refrigerants — evaporates, providing initial cooling and an increase in suction pressure compressor "p1". Due to the fact that the volume of gaseous refrigerant in the constant volume system increases, the discharge pressure "p2" increases in the circuit of the chiller. Due to restrictions on the discharge pressure for the compressor 7, according to the signal from the discharge pressure sensor 5, the programmable control unit 6 gives a signal to open the bypass solenoid valve 9, due to which a portion of the working medium of the chiller enriched with low boiling components is transferred from the liquid separator 10 to the receiver 1 gaseous phase. The discharge pressure "P2" in the cycle decreases, the bypass solenoid valve 9 closes. Due to the large suction pressure "p2" in the starting period, the solenoid valve 2 of the refrigerant composition control system is in the closed state. Thus, at the initial time, a significant part of the low boiling component is removed from the cycle; therefore, a mixture enriched in high boiling components circulates in the regenerative heat exchanger 12 and the evaporator 14. The isothermal choke effect for a given composition of the working fluid at higher boiling points is higher. This leads to a significant increase in the generated cooling capacity during the start-up period. As the boiling point decreases and condensation of the intermediate components of the mixed refrigerant begins, the discharge pressure “p2” decreases with time due to maintaining the suction pressure “p1” at a certain optimal level by reducing the flow area in the adjustable main throttling device 13. Programmable control unit 6 gives a signal to open the solenoid valve 2 at the values of the suction pressure "p1" and discharge "p2" at the same time below the optimum. The suction pressure “p1” is directly proportional to the cooling temperature and falls below the optimal set values at the beginning of the boiling of low-boiling components in the mixed working fluid of the refrigeration machine. After opening the solenoid valve 2, a portion of the refrigerant, enriched with low-boiling components, begins to throttle from the receiver 1 to the suction of the compressor 7, increasing the suction pressure "p1" and the discharge "p2" to optimal values, after which the solenoid valve of the output stream 2 closes. Therefore, in this case, the regulation of the composition of the refrigerant by the system is made by a combination of signals from the suction pressures "p1" and discharge "p2". Thus, the concentration of low-boiling components in the mixed refrigerant circulating in the evaporator 14 increases, and consequently, the isothermal choke effect also increases at given cooling temperatures. Due to the addition of low-boiling components to the working fluid, the hydraulic characteristic of the adjustable main throttling device 13 changes - the throttle begins to close the flow area until the optimum suction pressure "p1" is reached and at the same time, the discharge pressure "p2" begins to decrease. The cycle of the refrigerant composition control system closes. As the required cooling temperature is reached, the mixture of refrigerants in the receiver, enriched with low-boiling components, is completely throttled into the circuit of the chiller to a pressure in the receiver close to the suction pressure into the compressor. Thus, it is possible to organize stepwise cooling by ensuring the optimal composition of the multicomponent working fluid in the evaporator of the refrigeration machine.

The duration of opening and closing of the solenoid valve 2, as well as the values of the settings - the optimum operating pressures and hysteresis are set depending on the size of the chiller operating on this cycle, the type and composition of the working fluid.

Thanks to the use of the proposed system for controlling the composition of the refrigerant, the time for the chiller to enter the mode is significantly reduced, which leads to a gain in energy consumption.

The application of the proposed refrigerant composition control system significantly limits the operating time of the chiller at high discharge pressures (usually about 30 bar), which increases the reliability of the compressor and the chiller as a whole.

In addition, it is relevant to use this refrigerant composition control system for refrigerators designed to cool objects from ambient temperature to low temperature, to increase the cooling rate. In this case, the input signals for the programmable control unit 6 will already be a set of signals: the suction pressure to the compressor "p1", the discharge pressure of the compressor "p2" and the current cooling temperature.

Claims (2)

1. The refrigerant composition control system comprising a liquid separator located after the condenser and a bypass line with a sequentially located bypass solenoid valve, receiver and throttling device, characterized in that the refrigerant from the bypass line is sent directly to the suction to the compressor, while the refrigerant is supplied from the bypass line to the suction to the compressor is controlled by an additional solenoid valve located between the receiver and the throttling device a flow line, which is controlled by a programmable control unit. 2. The system according to p. 1, characterized in that the input signals for the programmable control unit is a combination of signals of the suction pressure and discharge of the compressor of the refrigeration machine.

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