REPRESENTATION OF PURE FLUID COEXISTENCE CURVES BY SERIES EXPANSION

We give a systematic recipe for constructing the coexistence curve associated with a pure fluid described by an analytical equation of state. The novelty of our result lies not in its theoretical basis, which is well known, but in the high degree of accuracy that it will routinely yield over a broad range of density and temperature for a relatively modest expenditure of computing effort. Our results are quite general: they may be applied to any analytical equation of state. The effectiveness of our method is illustrated by applying our general solution to four widely known model equations of state: van der Waals, Dieterici, Soave-Redlich-Kwong, and Carnahan-Starling with van der Waals tail term. These models show a considerable diversity of coexistence curve shapes, and our method yields accurate representations for each model. An investigation is also initiated of the representation of experimental coexistence curves that exhibit pronounced "non-classical" behavior over an appreciable range of densities. © 1990.