Estimation of transport properties of refrigerants

Abstract

Studies are being done to replace conventional refrigerants with alternatives that have less or no ozone depletion and greenhouse warming potential, yet possess appropriate properties for a refrigeration cycle. To achieve this goal a consistent set of thermodynamic and transport properties of the working fluid is required. The major problem with the possible alternative refrigerants is that sufficient experimental data do not exist, thus making it difficult to develop correlations that can predict properties in all regions including the vapor-liquid equilibrium. In this study, a generalized four-parameter transport equation that can predict viscosity and thermal conductivity is introduced. Four chosen characteristic parameters are critical temperature, critical pressure, acentric factor and a newly suggested fourth parameter. A transport property is assumed to take the form of a summation of ideal and residual contributions. The ideal contribution is derived from statistical thermodynamics, while the residual part is obtained by fitting the experimental or empirical data. By applying the Maxwell equilibrium condition, saturation properties can also be calculated. If the characteristic parameters are not available, they can be estimated from the group contribution method.