MFIX-Exa: CFD-DEM simulations of thermodynamics and chemical reactions in multiphase flows

MFIX-Exa is a CFD-DEM code for the numerical solution of chemically reacting multiphase flows (fluid and solids phases), specifically targeted for flows in complex reactor geometries. The fluid is modeled using a low Mach number formulation with a multicomponent ideal gas equation of state, which is imposed as a constraint of the velocity field. The fluid equations are discretized using an embedded boundary (EB) aware Godunov scheme with an approximate projection. The particles (that constitute the solids phase) are represented by a soft-sphere spring-dashpot model and evolved using a forward Euler method with subcycling. The fluid and particles models are coupled through a volume fraction field in addition to interphase mass, momentum, and energy transfer. The mathematical model and numerical approach are benchmarked against three different verification tests and validated with two separate tests. Also, a scaling analysis is provided. This manuscript represents the current state-of-the-art of MFIX-Exa and describes the major extensions to the previous work presented in Musser et al. (2021), including the Godunov time integration algorithm for the fluid phase and the inclusion of thermodynamics and chemistry modeling to both the fluid and solids phases.