Prediction of ternary azeotropic refrigerants containing ammonia

Abstract

Developing azeotropic refrigerants based on ammonia is a promising way to achieve better refrigeration performance and less refrigerant charge than using ammonia alone. In this paper, ammonia-based, homogenous ternary azeotropic refrigerants were predicted. The Peng-Robinson equation of state was combined with the non-random two-liquids (NRTL) to represent the vapor-liquid equilibrium (VLE) behavior of binary and ternary mixtures. The non-randomness binary interaction parameter α in NRTL model has a significant influence on the VLE description of the ammonia mixtures, while such influence is commonly weak in hydrocarbon or hydrofluorocarbon mixtures at α from 0.2 to 0.47. Empirically, α = 0.2 is more suitable for ammonia mixtures rather than the conventional default value 0.3. The azeotropic loci of the mixtures were determined by the extreme pressure method. Ten ternary systems were predicted, of which three maximum-point azeotropes were found, namely ammonia + n -butane + pentafluoroethane /1,1-difluoroethane /2, 3, 3, 3 - tetrafluoroprop-1-ene. The ternary azeotropes predicted are thought to be promising substitute refrigerants.