ON TUNING THE CCOR EQUATION PARAMETERS TO THE SATURATION CURVE

We analyze the possibility of obtaining a better representation of pur e fluid VL coexistence curves by the cubic chain-of-rotators (CCOR) eq uation of state, which, in the original form, has two temperature depe ndent parameters, alpha and gamma. Introducing separate gamma paramete rs for liquid and vapor phases, while retaining the common alpha param eter, has enabled description of saturation pressures and densities of coexisting phases with a high degree of accuracy. As one may expect, this improvement extends also to predictions of superheated vapor dens ities and subcooled liquid densities at low pressures. However, it has been shown that ''tuning'' the equation parameters to the saturation curve up to the critical point leads to a thermodynamically inconsiste nt description of compressed liquid at high pressures as well as to a dramatic increase of enthalpy prediction errors in the critical region . Three common substances, CO2, NH3 and H2O, are taken for illustratio n.