15.2.2 User Inputs for Wall Surface Reactions

The basic steps for setting up a problem involving wall surface reactions are the same as those presented in Section  15.1.1 for setting up a problem with only fluid-phase reactions, with a few additions:

1.   In the Species Model dialog box:

Models Species Edit...

(a)   Enable Species Transport, select Volumetric and Wall Surface under Reactions, and specify the Mixture Material. See Section  15.1.2 for details about this procedure, and Section  15.1.1 for an explanation of the mixture material concept.

(b)   (optional) If you want to model the heat release due to wall surface reactions, enable the Heat of Surface Reactions option.

(c)   (optional) If you want to include the effect of surface mass transfer in the continuity equation, enable the Mass Deposition Source option.

(d)   To control the robustness and the convergence speed, enter a value between 0 and 1 for the Aggressiveness Factor. A value of 0 (the default) is the most robust, but results in the slowest convergence.

(e)   (optional) If you are using the pressure-based solver and you want to include species diffusion effects in the energy equation, enable the Diffusion Energy Source option. See Section  15.2.4 for details.

(f)   (optional, but recommended for CVD) If you want to model full multicomponent (Stefan-Maxwell) diffusion or thermal (Soret) diffusion, enable the Full Multicomponent Diffusion or Thermal Diffusion option. See Section  8.9.2 for details.

2.   Check and/or define the properties of the mixture. (See Section  15.1.3.)

Materials

Mixture properties include the following:

• species in the mixture

• reactions

• other physical properties (e.g., viscosity, specific heat)

You will find all species (including the solid/bulk and site species) in the list of Fluent Fluid Materials. For a deposited specie such as Si, you will need both Si(g) and Si(s) in the materials list for the fluid material type.

Note that the final gas-phase specie named in the Selected Species list should be the carrier gas . This is because ANSYS FLUENT will not solve the transport equation for the final specie. Note also that any reordering, adding or deleting of species should be handled with caution, as described in Section  15.1.3.

3.   Check and/or set the properties of the individual specie in the mixture. (See Section  15.1.3.) Note that if you are modeling the heat of surface reactions, you should be sure to check (or define) the formation enthalpy for each specie.

4.   Set species boundary conditions.

Boundary Conditions

In addition to the boundary conditions described in Section  15.1.5, you will first need to indicate whether or not surface reactions are in effect on each wall. If so, you will then need to assign a reaction mechanism to the wall. To enable the effect of surface reaction on a wall, enable the Reaction option in the Species section of the Wall dialog box.

If you have enabled the global Low-Pressure Boundary Slip option in the Viscous Model dialog box, the Shear Condition for each wall will be reset to No Slip even though the slip model will be in effect. Note that the Low-Pressure Boundary Slip option is available only when the Laminar model is selected in the Viscous Model dialog box.

See Section  7.3.14 for details about boundary condition inputs for walls. See Section  7.2.3 for details about boundary condition inputs for porous media.