Thermodynamic performance prediction of pulse tube refrigeration with mixture fluids

A refrigeration cycle with two isentropic and two isobaric processes, referred to as the modified Brayton cycle, is introduced for predicting the thermodynamic performance of pulse tube refrigeration with a binary mixture refrigerant. The corresponding theoretical expressions of cooling power, thermodynamic efficiency and required work of a refrigeration cycle are established. Based on the prediction calculations for a number of cryogenic fluids, promising mixture pairs of working refrigerants are recommended. The computed results show that 9.5% of the coefficient of performance (COP) and 6.7% of the cooling power at 80 K could be gained if a mixture pair of 10% nitrogen and 90% helium is used instead of pure helium for the pulse tube refrigeration. The minor mixture pairs which have a positive effect on pulse tube refrigeration at temperatures near 80 K, including hydrogen-helium, argon-helium and neon-helium, are also discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.