Geometric acceleration of complex chemical equilibrium calculations — algorithm and application to two- and three-component systems

Abstract

A new accelerator algorithm was developed based on phase diagram geometry to include large number of equilibrium calculations into process and multiphysics models more efficiently. These models require thermochemical properties from equilibrium calculations such as phase compositions and phase fractions, heat capacity and enthalpy. When an equilibrium calculation is performed, the calculated thermochemical properties are stored in a geometrical database on the boundaries of the phase region at the calculated phase compositions. The developed accelerator can function with any commercial or open source equilibrium calculation software. In this work, ChemAppPy was used.

The lever rule can be used to interpolate thermochemical properties at any system composition within a phase region based on thermochemical properties stored on the phase region’s boundaries. It is therefore only necessary to discretise boundaries and not entire phase regions, except for single-phase regions. A generic form of the lever rule is presented that can be used in any phase region and in systems with any number of system components. The Gibbs phase rule is used to calculate the dimensionality of phase region boundaries and to determine the minimum number of equilibrium calculations needed to discretise these boundaries. This framework of established thermochemical theory provides a sound basis for the discretisation and interpolation routines of the algorithm and allows the accelerator to be used with systems with any number of components. The functionality of the accelerator algorithm was tested in a number of two- and three-component systems as these systems could still be easily visualised to verify the functioning of the newly developed algorithm.