Empirical equation of state for supercritical fluids

Abstract

An empirical equation of state for supercritical fluids has been derived based on the power laws and the thermodynamic equation of state P = ( ϖS/ ϖV) T T − ( ϖU/ ϖV) T . The equation of state derived in this work is given by p=P ∗(T)−a k(T)Xe −x−b k(T)[X+c k(T)] 4X where P ∗(T), a k (T), b k (T), and c k (T) are functions of temperature and suffix k means a state of fluid such as k = l for the liquid-like region V < V c and k = g for the gas-like region V > V c in the supercritical region T > T c . The quantity X is defined by X = ( V − V c )/ V where V c is the critical volume and T c is the critical temperature. The equation of state for five fluids, neon, hydrogen, deuterium, carbon monoxide, and helium is given by a modified form P=P ∗(T)−{a k(T)+b k(T)[X+c k(T)] 4}Xe −x Comparisons between the PV isotherms for methane calculated by the Benedict-Webb-Rubin (B-W-R), the Beattie-Bridgeman (B-B) equations of state and the equation of state in this work have been done and it is found that the present equation of state gives a good agreement with the data in the same order of accuracy as the B-W-R and B-B equations of state.