  The present study provide a systematic derivation of a phase-field version of
the momentum, mass and heat transport equations, while accounting for chemical
reactions in the fluid phase. To achieve this goal, the volume averaging
technique is used to reformulate the conservation equations in the presence of
multiple phases and their respective diffuse interfaces. A careful analysis,
and neglecting terms of the second order in fluctuations, reveals that the
structure of the multiphase/diffuse interface version of the conservation
equations is very similar to the original single phase/sharp interface
formulation. The multiphase character of the problem reflects itself in a
coupling term, which acts at the interface between two adjacent phases. The
model is then applied to the special case of a reactive fluid in contact with
an inert solid. Two coupling parameters are then introduced, which control the
exchange of momentum and heat at the interface. For a numerical study of the
thus obtained set of coupled partial differential equations, a hybrid lattice
Boltzmann-finite difference-phase field (LB-FD-PF) framework is proposed and
implemented in the open source software OpenPhase. The model is then thoroughly
validated via numerical simulations, including isothermal flow, non-reactive
non-isothermal flow, and reactive flows. To perform the simulations involving
chemical reactions, OpenPhase is coupled to the open-source chemical kinetics
software CANTERA, which delivers details of the chemical reaction mechanisms
and the necessary thermodynamic and transport properties of the reacting
chemical species. These simulations show that, once the coupling parameters are
adequately tuned, the present approach yields excellent agreement with the
sought for sharp interface method.
