A refrigeration cycle with two isentropic and two isobaric processes, refer
red to as the modified Brayton cycle, is introduced for predicting the ther
modynamic performance of pulse tube refrigeration with a binary mixture ref
rigerant. The corresponding theoretical expressions of cooling power, therm
odynamic efficiency and required work of a refrigeration cycle are establis
hed. Based on the prediction calculations for a number of cryogenic fluids,
promising mixture pairs of working refrigerants are recommended. The compu
ted 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% nitr
ogen and 90% helium is used instead of pure helium for the pulse tube refri
geration. The minor mixture pairs which have a positive effect on pulse tub
e refrigeration at temperatures near 80 K, including hydrogen-helium, argon
-helium and neon-helium, are also discussed. (C) 2000 Elsevier Science Ltd.
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