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Differential equations for critical curves of fluid mixtures



Ian Bell, Ulrich K. Deiters


A novel, particularly robust method for the calculation of critical curves of fluid mixtures is proposed that makes use of differential equations representing the critical conditions (isochoric thermodynamics formalism). These differential equations are integrated with adaptive numerical integration methods, thus avoiding the convergence problems that so often afflict methods using algebraic equations. The novel method can be used with all Helmholtz energy-explicit equations of state, including models that can return unphysical results when applied to thermodynamic states within a two-phase region, for example, the GERG equations of state. In combination with the "parametric marching" technique, the new approach is able to follow critical curves of arbitrary shape. The Supporting Information provides an implementation of this approach for the GERG-2008 and Peng–Robinson models in the Python language.
Industrial and Engineering Chemistry Research


critical points, phase equilibria


Bell, I. and Deiters, U. (2020), Differential equations for critical curves of fluid mixtures, Industrial and Engineering Chemistry Research, [online], (Accessed May 26, 2024)


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Created September 22, 2020, Updated January 19, 2023