Describes how the technique of rational approximation can be used to represent the liquid-vapour phase boundaries of nonazeotropic refrigerant mixtures. Specific representations are given for R131B/R152a. These rational approximations accurately represent the phase boundaries over a broad range of thermodynamic states that are relevant for models of heat pumps charged with this mixture. This type of representation is particularly appropriate for use in computer design and simulation models where calculational speed is a prime concern. The method used to generate the rational approximations can be extended to the entire two-phase liquid-vapour region, and it may also be easily adapted to other mixtures.

KEYWORDS: thermodynamics, properties, refrigerants, non azeotropic, mixtures, heat pumps, calculating