Predicting calorimetric properties using the original and the modified simplified-perturbed-hard-chain theory equations of state

Previous evaluations of the simplified-perturbed-hard-chain theory (SPHCT) equation of state (EOS) have documented its ability to predict the equilibrium and volumetric properties of many pure fluids and mixtures. Shaver et al. (Shaver, R. D., Robinson, R. L., Jr., and Gasem, K. A. M., 1995. Modified SPHCT EOS for improved predictions of equilibrium and volumetric properties of pure fluids, Fluid Phase Equilibria, 112: 223-248) have offered modifications to the SPHCT model, which have resulted in improved pure-fluid vapor pressure and phase density predictions. In this complementary work, we evaluate the predictive abilities of the SPHCT EOS for calorimetric properties. Specifically, the accuracy of enthalpy and entropy predictions using the SPHCT and its modifications are compared with those of the widely used Peng-Robinson (PR) EOS. Our evaluations were conducted for six pure fluids of varying chemical structure and covering the two-phase and single-phase regions. The results indicate that the abilities of the PR EOS, the original SPHCT EOS and the modified model to predict calorimetric properties are similar to their comparative abilities to predict volumetric properties. The absolute average percentage deviations obtained for liquid density, enthalpy, and entropy, respectively, are: 7.6%, 4.2% and 3.3% for PR; 7.3%, 9.1% and 5.6% for the original SPHCT; and 10.9%, 4.2% and 2.5% for the modified model. Further, the modified SPHCT EOS of Shaver et al. (1995) appears to be more accurate at predicting calorimetric properties than the original SPHCT model. (C) 1997 Elsevier Science B.V.