Simulation And Experimental Study On The Performance Of Air Cycle Refrigeration System Using Membrane Dehumidification

With natural working fluid as refrigerant, the air refrigeration system is of irreplaceable advantages. But it is not used widely because of its low COP. In addition, the water vapor in the compressed air condenses or freezes in the turbo-expander, which is the great harm to the safety of the turbo-expander and the whole system. Therefore, for further improving the performance of the air refrigeration system, a membrane dehumidi?er was used to separate the water vapor from the compressed air in this paper, which was intended to achieve the good dehumidification performance, reduce the energy consumption and improve the COP of the air refrigeration system.The steady mathematical model of the air refrigeration system with membrane dehumidification was established by adopting the lumped parameter method. Under the same working conditions, the performance of the system for three different heat regenerating schemes was simulated, the influence of the membrane dehumidi?er and the different heat regenerating schemes on the system performance were analyzed. In order to verify the simulation results, the performance of the air refrigeration system with membrane dehumidification for three different heat regenerating schemes was measured experimentally based on the simulation. In the meantime, the experimental results for the air refrigeration system with membrane dehumidification were compared these for the system with molecular sieve dehumidification. The following conclusion can be obtained from the numerical simulation and experimental results:(1) Compared with the air refrigeration system with molecular sieve dehumidification, the experimental results show that the amount of water vapor condensed in the turbine and the power consumption can be reduced significantly in the air refrigeration system with membrane dehumidification. Moreover, the COP of membrane dehumidification system is higher than that of the molecular sieve dehumidification system. Under the working condition that inlet pressure of the compressor is 200 k Pa, the amount of water vapor condensation and the power consumption of the membrane dehumidification system for two stage heat regenerating scheme is reduced about 51% and 20%, respectively, meanwhile the COP of the system is increased about 22%. Thus the use of membrane dehumidi?er can obtain the good dehumidification performance, reduce the energy consumption and improve the COP of system.(2) For the membrane dehumidi?er, the experimental results show that the air humidity ratio at the membrane dehumidi?er outlet decrease with the rise of the inlet pressure and the purging gas flow ratio, and increase with the rise of the total flow rate. Under the working condition that inlet pressure of membrane dehumidi?er is 600 k Pa, the total flow rate is 0.12 kg/min and the purging gas flow ratio is 20%, the air humidity ratio at the membrane dehumidi?er outlet is about 0.29 g/kg.(3) For the air cycle refrigeration system with membrane dehumidification, the experimental results show that the use of heat regenerator can increase the refrigerating capacity and improve the COP of the system, and the performance of the two stage heat regenerating scheme is the best. Under the working condition that inlet pressure of the compressor is 200 k Pa, the refrigerating capacity and COP of the system for the two stage heat regenerating scheme is about 3200 W and 0.18, which is increased about 78% and 80% compared with the none heat regenerating scheme, respectively.(4) The trend of the numerical simulation and experimental results are good agreement, but there are some errors. Under the working condition that inlet pressure of the compressor is 200 k Pa, a deviation between simulation and experimental results of the COP and the water vapor condensed in the turbine is about 10% and 18% in the air refrigeration system with membrane dehumidification for the two stage heat regenerating scheme, respectively. For the membrane dehumidi?er, under the working condition that inlet pressure of the membrane dehumidi?er is 400 k Pa and the total flow rate is 0.18 kg/min, a deviation between simulation and experimental results of the air humidity ratio at the membrane dehumidi?er outlet is about 20%.