Specifics of Calculating Thermophysical Properties of CO2 and R134a in Critical Point Using NIST REFPROP

Abstract

Thermophysical properties of various fluids (liquids, vapours, and gases) are the fundamental knowledge for the application of these fluids. A computer program can be considered as a very useful tool if it is able to calculate various thermophysical properties of various fluids within a wide range of pressures and temperatures from lower ones and up to critical and supercritical ones. NIST REFPROP is such a program. For tens of years, it can be possibly considered as the best one in the world. However, it is not absolutely perfect. In the previous versions(s) of the NIST REFPROP 9.1 and lower, three basic thermophysical properties, specific heat, thermal conductivity, and volumetric expansivity, were subjected to very significant variations within the critical region. They had almost infinite peak values in the critical point, which was a theoretical approach. In 2018, the latest version was released, Ver. 10.0 (https://www.nist.gov/srd/refprop). It was updated with new fluids, a wider range of pressures and temperatures, and with improved equations / correlations. The objective of this paper is to check if the deficiencies occurred in the previous version(s) have been fixed in NIST REFPROP Ver. 10.0. In this paper, various thermophysical properties of CO2 and R134a have been calculated by using NIST REFPROP Ver 10.0. The results around the critical point have been analyzed.