refrigerant-oil mixtures, refrigeration, phase equilibrium, cycle analysis, departure functions
A method to estimate the performance of single-stage vapor compression refrigeration systems as a function of the oil circulation ratio is presented. The model is based on the Peng-Robinson equation of state and on the theory of departure functions to estimate the mixture enthalpy, entropy and specific volume as a function of pressure, temperature and mixture composition. The method is applied to a mixture of isobutane (R-600a) and alkyl benzene oil. Pressure-enthalpy diagrams are presented as a function of the oil circulation ratio. These are used in conjunction with a thermodynamic cycle analysis in which the behavior of overall performance parameters such as cooling capacity, compressor power and coefficient of performance are compared with those obtained for the baseline (i.e., pure refrigerant) condition.