| The air cycle refrigeration system has a good development prospect because of its excellent characteristics of non polluting working medium and simple system structure.However,due to the high moisture content in the air,the water vapor in the air will condense into droplets or even freeze at a lower temperature,which seriously affects the stable operation of the system and the refrigeration performance of the system.The research on dehumidification of air cycle refrigeration system is carried out to lay a foundation for improving the performance of air cycle refrigeration system,and to improve the durability and reliability of system operation.In view of the unstable operation of the original air refrigeration cycle system and the high moisture content in the system,this paper redesigns and adds the membrane dehumidification module.The dehumidification effect and system performance of the improved system are analyzed theoretically and experimentally.Firstly,based on the lumped parameter method and the energy conservation equation,the mathematical model of each part of the system is established,and the simulation program is compiled with MATLAB.The influences of different scavenging methods,membrane dehumidification module inlet pressure,compressor inlet pressure and ambient temperature on the dehumidification effect and system performance are analyzed under dry air and wet air conditions.Secondly,the original air cycle refrigeration system was rebuilt,and the membrane dehumidification module was designed and newly added.The system was dehumidified by using the difference of water vapor pressure between two sides of the membrane in the membrane dehumidifier as the driving force.The dehumidification performance and refrigeration performance of the system are studied under the condition of variable working conditions.The influences of the inlet pressure of membrane dehumidification module and compressor on the dehumidification performance and refrigeration performance of the system are analyzed.The simulation and experimental results are as follows:(1)The simulation results show that the external scavenging can save part of the dry gas consumed in the self scavenging mode,and the average COP of the system can be increased by 25.3% under the same regenerative cycle.(2)The results of wet air simulation show that with the increase of the inlet pressure of the membrane dehumidification module,the moisture content of the inlet air and the condensation of water vapor in the turbine expander decrease gradually under the three kinds of regenerative cycles.In the secondary regenerative cycle,the moisture content inthe inlet air of the turbo expander can be reduced by 73.9%,and the condensation capacity of water vapor in the expander can be reduced by 75.5%.When the inlet pressure of the membrane dehumidification module is 700 kPa,the moisture content in the inlet air of the turbo expander is 0.049g/kg,and the condensation capacity of water vapor in the turbo expander is 0.043g/kg.With the increase of inlet pressure of compressor,the condensation amount of water vapor in the expander increases gradually under different inlet pressure of membrane dehumidifier.When the inlet pressure of the membrane dehumidification module is 700 kPa,the inlet pressure of the compressor increases from 160 kPa to 200 kPa,and the condensation amount of water vapor in the turbine expander increases from0.013g/kg to 0.043g/kg.With the decrease of the ambient temperature,the moisture content in the inlet air and the condensation of water vapor in the expander gradually decrease.Under the secondary regenerative cycle,the ambient temperature is reduced from 20℃ to0℃,and the moisture content in the inlet air of the turbo expander is reduced by 67.7%.When the ambient temperature is 0℃,the lowest moisture content in the inlet air of the turbo expander is 0.02g/kg,and the condensation of water vapor in the turbo expander is0.018g/kg.(3)The results of wet air simulation show that with the increase of compressor inlet pressure,the outlet temperature of turbo expander decreases gradually,and the cooling capacity and COP of the system increase gradually.When the inlet pressure of the compressor is 200 kPa,the minimum outlet temperature of the turbo expander is-60.6℃,and the cooling capacity and COP of the system are 5.26 kw and 0.128 respectively.With the decrease of the ambient temperature,the outlet temperature of the turbo expander decreases gradually,and the cooling capacity and COP of the system increase gradually.In the second cycle,the ambient temperature decreased from 20℃ to 0℃,the outlet temperature of turbo expander decreased by 14.4%,the cooling capacity and COP of the system increased by 29.8% and 34.2%,respectively.At 0℃,the lowest outlet temperature of turbo expander is-67 ℃,and the cooling capacity and COP of the system are 6.36 kw and 0.16 respectively.(4)The dry air simulation results show that the cop of the system decreases with the increase of the power consumption of the system.The system power consumption increased by 72.2% when the air source pressure increased from 200 kPa to 750 kPa.The maximum cop of the system is 0.448 when the air source pressure is 200 kPa.The cooling capacity and COP of the system are also increased with the decrease of the ambient temperature.The cooling capacity and COP of the system are 5.57 kw and 0.57 respectively at the ambient temperature of 0℃.(5)The experimental results show that the increase of the inlet pressure of themembrane dehumidification module can effectively improve the dehumidification effect of the system.The inlet pressure of the membrane dehumidification module is increased from300 kPa to 700 kPa.Under the secondary regenerative cycle,the intake moisture content of the turbine expander is reduced by 36.4%,the condensation of water vapor is reduced by58.5%,but the cop of the system is reduced from 0.25 to 0.13.When the inlet pressure of the membrane dehumidification module is 700 kPa,the minimum moisture content of the inlet air of the turbine expander is 0.107g/kg.At this time,the condensation amount of water vapor in the turbine expander is only 0.044g/kg.(6)The experimental results show that the increase of the compressor inlet pressure has little effect on the dehumidification performance of the system,but with the increase of the compressor inlet pressure from 160 kPa to 200 kPa,the exhaust temperature of the turbo expander decreases by 11.9℃,the cooling capacity of the system increases by 1.41 kw,and the maximum COP of the system is 0.16. |
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