A modified Kardos equation for the thermal conductivity of refrigerants

This work presents a modification of the Kardos equation specifically oriented to refrigerants. The proposed equation was tested for both liquid and vapor thermal conductivities along saturation of the main refrigerants. In the Kardos equation, the thermal conductivity of liquids is a function of the density of the liquid, heat capacity at constant pressure, speed of sound in the liquid and average distance between the centers of the molecules. In the present version, the liquid molar volume and the distance between the surfaces of adjacent molecules were replaced by two constant parameters widely available for all the fluids: the critical density and radius of gyration. In this way, the resulting equation is much simpler, still being a scaled equation. In the proposed equations, an adimensional factor was regressed to minimize the deviations. The final equations were able to predict the thermal conductivity with AAD(L) = 3.6% for liquids and AAD(V) = 9.8% for vapors.