Vapor-Liquid Equilibrium Equations for Hydrocarbon Oil Mixtures

The world of refrigeration is now reviewing the use of hydrocarbons (R290 and R600a) as working fluids for heat pump and refrigeration systems. With the arrival of CFCs, in the 1930's, these fluids were discarded on an almost exclusively flammability criterion basis. However, the trend now has reversed as CFCs are being phased out. Even though their thermodynamic and transport properties have been extensively studied, little is known on how hydrocarbons are affected by the presence of oil. The present article suggests an extension of a known methodology, originally developed for CFCoil mixtures, to deal with hydrocarbon-oil mixtures. It features the usefulness of Raoult's law and FieryHuggins polymer solution theory to tackle vapor-liquid equilibrium problems encountered in numerical simulation models. INTRODUCTION The search for thermodynamically sound and environmentally acceptable alternative refrigerants has dominated the world of refrigeration in the last ten years. There seems to be little doubt now that the decomposition of CFC' s in the stratosphere, releasing chlorine atoms, is the principal cause for the depletion of the ozone layer. And, while scientists are trying to establish the truly occurring reactions in the stratosphere, refrigeration engineers are looking for ecologically better fluids. Hence the revival of hydrocarbons as working fluids in refrigeration systems. And if they are not a panacea for all refrigeration applications they are, at least, viewed as a substitute for the ozone-harmful conventional fluids. They may even offer favorable thermodynamic or heat transfer properties but their flammability has to be taken in account, specially when used in domestic refrigerators (Lorentzen, 1994; Giinther, 1994). Properties of refrigerant hydrocarbon-oil mixtures play a fundamental role in refrigeration equipment design and are an important aid in numerical simulation models which are eventually used by manufacturers. The presence of oil affects the thermodynamic (and transport) properties of pure refrigerants, altering equipment sizing and perfonnance.