The Modified Trebble-Bishnoi equation of state

Date
1990
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
An inconsistency in thermodynamic property prediction using the Trebble- Bishnoi equation of state was recently identified by scientists at the Shell research center in Amsterdam. Specifically, it was found that the Trebble-Bishnoi equation of state predicted negative values of isochoric heat capacity and imaginary values for speed of sound at extremely low temperatures. Subsequent investigation has led to the conclusion that any temperature dependence whatsoever in the covolume term of van der Waals type equations will re~ult in anomalies in the predicted thermodynamic properties of pure fluids at extreme conditions. This work presents a discussion of the implication of temperature dependence in the Trebble-Bishnoi equation of state parameters and describes a modification to the equation in which temperature dependence is completely removed from the covolume term. By altering the temperature dependence in the attractive parameter, it is possible to correlate liquid-vapor phase behaviour with the modified equation more accurately than with the original equation, and the inconsistency has been corrected. The _modified equation was examined further through the calculation of eight thermodynamic properties in liquid-vapor regions over a very broad range of temperature and pressure. Predictions of second virial coefficients, internal energy, enthalpy, entropy, isobaric and isochoric heat capacities, speed of sound, and Joule-Thomson coefficients were compared to experimental data and to properties calculated using the Peng-Robinson equation of state. Results from the modified equation are of reasonable accuracy and are comparable to those obtained from the Peng-Robinson equation. No thermodynamic anomalies were detected for either equation of state apart from the fact that an infinite value for isochoric heat capacity is not predicted at the critical point. Having developed a satisfactory model for describing liquid-vapor regions, it was desirable to extend the equation of state to pure solids so that consistent calculation of solid-vapor equilibria could also be achieved. Based on correct thermophysical constraints and utilizing solid heat capacity, solid density and heat of sublimation at the triple point, a methodology is presented for extending the use of the equation of state to pure solids. The methodology is tested through the predictions of PVT behaviour and isobaric heat capacities for solids from their triple points to very low reduced temperatures. It is found that there are no negative heat capacity predictions and that an equation of state with at least four parameters is required to provide good prediction of solid-vapor phase behavior. Also discussed is the estimation of binary interaction parameters for binary solid-supercritical fluid systems using classical equation of state mixing rules and a common flash algorithm.
Description
Bibliography: p. 122-127.
Keywords
Citation
Salim, P. H. (1990). The Modified Trebble-Bishnoi equation of state (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/13192
Collections