Solubility of Refrigerants in Various Lubricants

Abstract

Solubility data of refrigerant/lubricant mixtures have been modeled with cubic equations of state (EOS): van der Waals (vdW), Soave-modified Redlich–Kwong (SRK), or Peng–Robinson (PR) types. The temperature dependence on the “a” parameter in the EOS is modeled with a common empirical function for pure refrigerants, including oils. For lubricants, a hypothetical oil (UniOIL) has been developed with universal oil EOS constants, and it is valid for any kind of lubricant oil. Only an average molecular weight is required for any type of oil. The mixing rules for the a and b parameters of EOS are more general than the ordinary van der Waals–Berthelot formula, and a justification of such mixing rules is discussed. The refrigerants studied are R-32, R-125, R-134a R-143a, R-152a, R-12, R-22, R-123 and R-13B1. The lubricants are naphthenic mineral (MO), alkylbenzene (AB/HAB), and polyol ester (POE) oils, as well as model compounds with pure component oils (hydrocarbons and POE). They are all analyzed with the UniOIL model. Good quality experimental solubility (PTx) data were selected from the literature and well correlated within their experimental uncertainties. All the cubic EOS (vdW, SRK, and PR) having the same type of mixing forms for the a and b parameters showed excellent fits to the experimental PTx data with essentially the same degree of accuracy. The results in this report are shown with the SRK type EOS.