Comparison of the cubic equations of state and different transport properties models for ORC turbines modeling

Abstract

The present paper focuses on a comparison of cubic equations of state (EoS) with accurate Span-Wagner (SW) EoS. Aungier Redlich-Kwong (ARK) EoS, Soave Redlich-Kwong (SRK) EoS and standard Peng-Robinson (PR) EoS were chosen as the basic EoS implemented into ANSYS CFX commercial solver. Furthermore, modeling of transport properties was also considered. Rigid Non Interacting Sphere (NIS) and Interacting Sphere (IS) viscosity models were chosen for a comparison with REFPROP data. Analytically calculated density and viscosity were compared with the REFPROP values for 1 polar (ethanol) and 2 non-polar (R245fa, MDM) fluids at the first part of the investigation. This part showed no significant difference between compared EoS for the non-polar fluids and slightly lower accuracy of PR EoS for the polar fluid. A significant difference between NIS and IS models was showed. 2D CFD simulations of VKI LS-89 cascade were performed for both MDM and MD4M siloxanes at the second part. It was showed that a preliminary analysis of the fundamental gasdynamic derivative behavior for isentropic expansion is needed for choosing of an appropriate cubic EoS. The choice of NIS or IS transport models does not show a significant effect on the obtained results.