Analysis of economizer application under compression refrigeration cycle
DATE:2024-10-16
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In addition, in the air conditioning conditions, the use of economizer cycle structure in the refrigeration system also has certain practical applications, such as Dunham Bush (Dunhum-Bush) of the vertical totally enclosed screw chiller WCFX series using medium-pressure make-up gas economizer cycle, so that the unit's refrigeration capacity increased by 16.7%; Carrier (Carrier) of the 30XA series of screw air-cooled chiller designed to improve the expansion valve, the economizer cycle. Carrier's (Carrier) 30XA series screw air-cooled chiller designed to improve the economizer cycle to improve the expansion valve inlet refrigerant subcooling degree, significantly increase the unit's refrigeration capacity and further enhance the unit's refrigeration efficiency and so on. However, there is no uniform conclusion on the energy-saving effect of adopting this system in air-conditioning conditions.
Due to the existence of the economizer, the compression process of the screw refrigeration compressor is divided into the following three main stages:
The first stage (the first stage of the compression process 1 ~ 2): by the screw compression, so that the refrigerant vapor M1 kg / s from the evaporator from the state point 1 adiabatic compression to the state point 2;
The second stage (intermediate make-up process 2~3): the αM1 kg/s make-up gas from the economizer with an intermediate pressure of pm flows into the primitive volume through the make-up gas orifice and mixes with the gas compressed by the screw to point 2. This process is regarded as an isovolumetric adiabatic filling of an ideal gas. The increase of gas pressure in the base element volume of the compressor is mainly the result of both the compression of the gas by the reduction of the base element volume and the filling of the base element volume by the intermediate make-up pipe. When there is no non-return valve on the charge line, this may result in a return flow of gas from the primitive volume. Therefore, the process is essentially an “inflation-compression” mixing process;
The third stage (secondary compression process 3~4): similar to the first stage, the gas (1+α)M1 kg/s is compressed from state 3 to state 4 in the compressor through the continuous reduction of the primitive volume.
The improved performance of the economizer for refrigeration units under air conditioning operating conditions can also be verified by some industrial experiments. This experiment is carried out on a screw-type chiller unit in an enterprise, which consists of a compressor, a shell-and-tube condenser, an expansion valve, and a full-liquid evaporator, etc. The main working conditions are as follows: the evaporating temperature is from 2℃ to 6℃, the condensing temperature is from 36.6℃ to 36.8℃, the condenser outlet subcooling degree is from 3.4℃ to 3.5℃, the compressor suction superheat degree is from 1.2℃ to 1.3℃, the refrigerant is R22, and the economizer is from 2 to 6℃. The refrigerant is R22.
The degree of performance improvement of the economizer screw cycle refrigeration system under air-conditioning conditions and the influence of different parameters on the system performance are discussed through cycle simulation analysis. The simulation results also show that the relative growth rate of the cooling capacity ranges from 6.4% to 12.8%, the relative growth rate of the coefficient of performance ranges from 2.2% to 6.5%, and the relative growth rate of the electric power ranges from 3.5% to 6.0%. In addition, after the addition of economizer to the screw cycle system, the growth rate of the coefficient of performance has an optimal value at a certain make-up air position; the higher the heat exchange performance of the economizer, the smaller the subcooling degree of the condenser outlet, and the lower the evaporation temperature, the better the degree of improvement of the system performance; and the growth rate of the coefficient of performance of the system with R134a as the refrigeration agent is higher than that of the case with R22 as the agent.
Large air-cooled heat pump chiller-heater unit economizer operation as the main source of central air conditioning, air-cooled heat pump chiller-heater unit has been widely used, and its stand-alone capacity is getting bigger and bigger, currently up to 1600kW or so, and large-scale air-cooled heat pump chiller-heater unit to the use of screw compressors mostly. From the use of large air-cooled heat pump chiller-heat exchanger unit, to improve the reliability of its winter operation, heating capacity, and operating efficiency is the key to improve its performance. According to the operating characteristics of the screw compressor, the use of economizer operation mode, the compressor for the intermediate make-up air, can realize the quasi-secondary compression, improve the operating characteristics of the compressor. Figure 1 for the experimental prototype system schematic diagram, heat exchanger type economizer process from the high-pressure liquid reservoir out of the liquid refrigerant into the economizer, in the inlet of the economizer, by the heat exchanger type economizer regulator valve bypass leads out a small portion of the refrigerant, through the heat exchanger type economizer regulator valve throttling, and the main stream of refrigerant for heat exchange, the mainstream refrigerant and therefore increase the degree of subcooling, and vaporization of the tributaries The refrigerant enters the compressor through the compressor charge port. Figure 2 shows the pressure-enthalpy diagram of the heat exchanger economizer operation. The working process of flash economizer is as follows: the refrigerant flowing out of the high-pressure liquid storage device is throttled before entering the flash economizer, and the refrigerant entering the flash evaporator is divided into two layers of vapor and liquid, the gas refrigerant enters into the make-up port of the screw compressor from the air-intake pipe, and the liquid refrigerant enters into the evaporator after throttled for the second time, and the pressure and enthalpy diagram of the operation of the flash economizer is shown in Fig. 3.
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Due to the existence of the economizer, the compression process of the screw refrigeration compressor is divided into the following three main stages:
The first stage (the first stage of the compression process 1 ~ 2): by the screw compression, so that the refrigerant vapor M1 kg / s from the evaporator from the state point 1 adiabatic compression to the state point 2;
The second stage (intermediate make-up process 2~3): the αM1 kg/s make-up gas from the economizer with an intermediate pressure of pm flows into the primitive volume through the make-up gas orifice and mixes with the gas compressed by the screw to point 2. This process is regarded as an isovolumetric adiabatic filling of an ideal gas. The increase of gas pressure in the base element volume of the compressor is mainly the result of both the compression of the gas by the reduction of the base element volume and the filling of the base element volume by the intermediate make-up pipe. When there is no non-return valve on the charge line, this may result in a return flow of gas from the primitive volume. Therefore, the process is essentially an “inflation-compression” mixing process;
The third stage (secondary compression process 3~4): similar to the first stage, the gas (1+α)M1 kg/s is compressed from state 3 to state 4 in the compressor through the continuous reduction of the primitive volume.
The improved performance of the economizer for refrigeration units under air conditioning operating conditions can also be verified by some industrial experiments. This experiment is carried out on a screw-type chiller unit in an enterprise, which consists of a compressor, a shell-and-tube condenser, an expansion valve, and a full-liquid evaporator, etc. The main working conditions are as follows: the evaporating temperature is from 2℃ to 6℃, the condensing temperature is from 36.6℃ to 36.8℃, the condenser outlet subcooling degree is from 3.4℃ to 3.5℃, the compressor suction superheat degree is from 1.2℃ to 1.3℃, the refrigerant is R22, and the economizer is from 2 to 6℃. The refrigerant is R22.
The degree of performance improvement of the economizer screw cycle refrigeration system under air-conditioning conditions and the influence of different parameters on the system performance are discussed through cycle simulation analysis. The simulation results also show that the relative growth rate of the cooling capacity ranges from 6.4% to 12.8%, the relative growth rate of the coefficient of performance ranges from 2.2% to 6.5%, and the relative growth rate of the electric power ranges from 3.5% to 6.0%. In addition, after the addition of economizer to the screw cycle system, the growth rate of the coefficient of performance has an optimal value at a certain make-up air position; the higher the heat exchange performance of the economizer, the smaller the subcooling degree of the condenser outlet, and the lower the evaporation temperature, the better the degree of improvement of the system performance; and the growth rate of the coefficient of performance of the system with R134a as the refrigeration agent is higher than that of the case with R22 as the agent.
Large air-cooled heat pump chiller-heater unit economizer operation as the main source of central air conditioning, air-cooled heat pump chiller-heater unit has been widely used, and its stand-alone capacity is getting bigger and bigger, currently up to 1600kW or so, and large-scale air-cooled heat pump chiller-heater unit to the use of screw compressors mostly. From the use of large air-cooled heat pump chiller-heat exchanger unit, to improve the reliability of its winter operation, heating capacity, and operating efficiency is the key to improve its performance. According to the operating characteristics of the screw compressor, the use of economizer operation mode, the compressor for the intermediate make-up air, can realize the quasi-secondary compression, improve the operating characteristics of the compressor. Figure 1 for the experimental prototype system schematic diagram, heat exchanger type economizer process from the high-pressure liquid reservoir out of the liquid refrigerant into the economizer, in the inlet of the economizer, by the heat exchanger type economizer regulator valve bypass leads out a small portion of the refrigerant, through the heat exchanger type economizer regulator valve throttling, and the main stream of refrigerant for heat exchange, the mainstream refrigerant and therefore increase the degree of subcooling, and vaporization of the tributaries The refrigerant enters the compressor through the compressor charge port. Figure 2 shows the pressure-enthalpy diagram of the heat exchanger economizer operation. The working process of flash economizer is as follows: the refrigerant flowing out of the high-pressure liquid storage device is throttled before entering the flash economizer, and the refrigerant entering the flash evaporator is divided into two layers of vapor and liquid, the gas refrigerant enters into the make-up port of the screw compressor from the air-intake pipe, and the liquid refrigerant enters into the evaporator after throttled for the second time, and the pressure and enthalpy diagram of the operation of the flash economizer is shown in Fig. 3.