Species transport, as described in Species Transport and Finite-Rate Chemistry, can also be applied to multiphase flows. You can choose to solve the conservation equations for chemical species in multiphase flows by having Ansys Fluent, for each phase , predict the local mass fraction of each species, , through the solution of a convection-diffusion equation for the species. The generalized chemical species conservation equation (Equation 7–1), when applied to a multiphase mixture can be represented in the following form:

(14–665)

where is the net rate of production of homogeneous species by chemical reaction for phase , is the mass transfer source between species and from phase to , and is the heterogeneous reaction rate. In addition, is the volume fraction for phase and is the rate of creation by addition from the dispersed phase plus any user-defined sources.

Ansys Fluent treats homogeneous gas phase chemical reactions the same as a single-phase chemical reaction. The reactants and the products belong to the same mixture material (set in the Species Model dialog box), and hence the same phase. The reaction rate is scaled by the volume fraction of the particular phase in the cell.

The set-up of a homogeneous gas phase chemical reaction in Ansys Fluent is the same as it is for a single phase. For more information, see Species Transport and Finite-Rate Chemistry. For most multiphase species transport problems, boundary conditions for a particular species are set in the associated phase boundary condition dialog box (see Defining Multiphase Cell Zone and Boundary Conditions in the User's Guide), and postprocessing and reporting of results is performed on a per-phase basis (see Postprocessing for Multiphase Modeling in the User’s Guide).

For multiphase species transport simulations, the Species Model dialog box allows you to include Volumetric, Wall Surface, and Particle Surface reactions. Ansys Fluent treats multiphase surface reactions as it would a single-phase reaction. The reaction rate is scaled with the volume fraction of the particular phase in the cell. For more information, see Species Transport and Finite-Rate Chemistry.

The species of different phases is entirely independent. There is no implicit relationship between them even if they share the same name. Explicit relationships between species of different phases can be specified through mass transfer and heterogeneous reactions. For more information on mass transfer and heterogeneous reactions, see Including Mass Transfer Effects and Specifying Heterogeneous Reactions in the User's Guide, respectively.

Some phases may have a fluid material associated with them instead of a mixture material. The species equations are solved in those phases that are assigned a mixture material. The species equation above is solved for the mass fraction of the species in a particular phase. The mass transfer and heterogeneous reactions will be associated with the bulk fluid for phases with a single fluid material.