Combination of multicomponent equilibria with CFD in modeling fast reactive processes

The thermodynamic software ChemApp was ported to the CFD software Fluent via user defined func-tions to facilitate solving of equilibrium chemistry simultaneously with CFD modeling of species mixing. In this approach, Fluent is used to solve the species transport without chemical reactions and the chemical equilibrium in each control volume is solved using ChemApp. Two methods to use the output of the ChemApp solver, i.e. the equilibrium concentrations of the chemi-cal species, were considered: In the first method, each computational cell in the CFD mesh was assumed to be ideally mixed, and the species concentrations were forced to the thermodynamic equilibrium values. The second method assumes that the equilibrium state is reached only in the turbulent fine structures re-sponsible for micromixing. The eddy dissipation concept (EDC) was then used to calculate the species mass transfer between the fine structures and the surrounding fluid. A neutralization process, where so-dium hydroxide solution was neutralized in a stirred reactor by adding dissolved carbon dioxide in the mixture, was used as a test case for the modeling approach.