Thermal Conductivity Modeling of Pure Refrigerants in a Three-Parameter Corresponding States Format

The potential of the corresponding states (CS) principle for modeling a pure fluid thermal conductivity surface is studied here. While for thermodynamic properties and for viscosity, successful results have been previously obtained by directly applying an improved three-parameter CS method, significant difficulties were encouIntered while trying to extend this method to thermal conductivity and, in particular, it fails if applied without separately dealing with the dilute-gas term, and the residual and critical enhancement contributions. These last two parts are also combined in the excess term. It is shown that the dilute-gas term cannot be expressed in such a format, and it has necessarily to be individually modeled for each target fluid. On the contrary, the excess contribution can be described through a specific conductivity scaling factor that can be individually determined from a single saturated liquid conductivity experimental value. The model for the excess part is set up in a three-parameter CS format on two reference fluids, in the present case, methane and R134a, for which dedicated thermal conductivity equations are available, and it has a predictive character. The models for the dilute-gas and for the excess contributions are then combined to give the final TC model. The model has been successfully validated for two homologous families of refrigerant fluids obtaining an AAD of 3.67% for 3332 points for haloalkanes and an AAD of 2.87% for 354 points for alkanes.