The Calculation of the Refrigeration Performance Based on Azeotropic Mixtures Containing Ammonia

Ammonia is a natural refrigerant with excellent thermodynamic properties, zero ozone depleting potential (ODP) and very low global warming potential (GWP). However, the poisonousness and flammability of ammonia limited its civil application. Besides, ammonia is immiscible with mineral lubricants, which may lead to a weakened heat transfer coefficient due to the film of oil presented in the evaporator. One of the most promising ways to extend ammonia's application in refrigeration systems is searching for new refrigerant mixtures based on ammonia. The improved properties of working agent were offered in the way to mix pure ammonia with other refrigerants having low values of GWP and zero ODP. In this paper, an evaluation of mixed refrigerants based on ammonia in the vapour compression refrigeration system was performed, synthetically considering the coefficient of performance(COP), volumetric refrigeration capacity(VRC) and discharge temperature. Both binary and ternary azeotropic mixtures were investigated, along with some commercial zeotropic refrigerants as references. The mixed thermodynamic properties were calculated by Peng - Robinson equation of state with the regressed interaction parameters. The COP of the mixtures was generally lower than that of the individual refrigerants, except for some azeotropic systems comprising of ammonia and hydrofluorocarbons. The discharge temperatures of all the azeotropic refrigerants were attractile, especially for ammonia's mixtures. The present results suggest the superiorities of the azeotropic refrigerants, especially for binary and ternary systems including ammonia.