Species transport, as described in Chapter 14, can also be applied to multiphase flows. You can choose to solve the conservation equations for chemical species in multiphase flows by having 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 14.1-1), when applied to a multiphase mixture can be represented in the following form:
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.
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 panel), 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 FLUENT is the same as it is for a single phase. For more information, see Chapter 14. For most multiphase species transport problems, boundary conditions for a particular species are set in the associated phase boundary condition panel (see Chapter 23.9.8), and postprocessing and reporting of results is performed on a per-phase basis (see Section 23.15).
For multiphase species transport simulations, the Species Model panel allows you to include Volumetric, Wall Surface, and Particle Surface reactions. 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 Chapter 14.
| To turn off reactions for a particular phase, while keeping the reactions active for other phases. turn on
Reactions in the
Species Model panel. Then, in the
Materials panel, select
none from the
Reactions drop-down list.
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 Section 23.9.7 and Section 23.9.6, 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.