About the physical validity of attaching the repulsive terms of analytical EOS models by temperature dependencies

Development of the translated-consistent tc-PR and tc-RK cubic equations of state for a safe and accurate prediction of volumetric, energetic and saturation properties of pure compounds in the sub- and super-critical domains

“…It is indeed well established that temperature-dependent volume translations, which could lead to accurate liquid densities all along the saturation line and in particular very near to the critical point, are thermodynamically inconsistent since they induce the crossing of isotherms in a (pressure, volume) plane as well as negative heat capacities [31][32][33]. It would be obviously unconceivable to develop inconsistent EoS and consequently, the proposed volumetranslation parameter was selected constant.…”

Testing the ability of various equations of state to reproduce high-pressure isotherm crossings in the (α, P) plane

“…where b -named excluded volume or covolume -depends on the pure-fluid critical properties T c and P c but does not depend on temperature [16]. The attractive term can (nearly) always be written in the general form:…”

About the numerical pitfalls characteristic for SAFT EOS models

“…Two-phase envelopes of pure nitrogen predicted by CK-SAFT [8]; ᭹, experimental data [21]. as recently demonstrated by Kalikhman et al [16]. In particular, it has been proven that any temperature dependency of the covolume necessarily results in infinite negative value of the isochoric heat capacity at the infinite pressure.…”

“…The latter phenomena might affect different models with the different degree of extend. While some models, such as the CK-SAFT of Huang and Radosz [8], exhibit the negative isochoric heat capacities at the extremely high pressures (the reason will be dis- cussed below), irrelevant for most practical implementations, the other ones might yield the non-physical predictions at much lower pressures [16].…”