A new method to calculate and predict thermodynamic properties of nonpolar, polar and quantum fluids at high temperatures

Abstract

As the only known equation of state (EOS) with the rigid theoretical foundation, the virial equation of state (VEOS) can be reliable enough to describe real-gas imperfection for low-to-moderate densities when truncated after the second or third virial coefficient. In our previous work, on the basis of the corresponding state principle, the generalized second and third virial coefficient models were proposed for nonpolar, polar and quantum fluids in a wide temperature range. In this work, combined with the ideal heat capacities, the high-temperature performance of the truncated VEOSs was evaluated on derived thermodynamic properties including speed of sound, isobaric heat capacity, entropy and internal energy. The criterion for being “valid” is defined as 1% relative deviation from the multiparameter EOSs, and this work presents the valid density and pressure regions of the truncated VEOSs for the derived thermodynamic properties. The truncated VEOSs have valid densities of the saturated densities below the critical temperatures, and have valid densities that tend to be constant beyond the critical temperatures. The SRK EOS is chosen as the representative of generalized EOSs. By the comparisons with the SRK EOS, the truncated VEOSs show the advantage in stability and universality. The truncated VEOSs can give a reliable extrapolation with wide applicable pressure ranges at high temperatures for nonpolar, polar and quantum fluids. The applicable density regions of the truncated VEOSs for derived thermodynamic properties are recommended to be the valid density regions of the pvT property. The applicable temperature ranges of the truncated VEOSs for derived thermodynamic properties are determined by the temperature ranges of the available ideal heat capacity data.