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14.2.3 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  14.1.2 for setting up a problem with only fluid-phase reactions, with a few additions:

1.   In the Species Model panel:

Define $\rightarrow$ Models $\rightarrow$ Species $\rightarrow$ Transport & Reaction...

(a)   Enable Species Transport, select Volumetric and Wall Surface under Reactions, and specify the Mixture Material. See Section  14.1.3 for details about this procedure, and Section  14.1.2 for an explanation of the mixture material concept.

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

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

(d)   (optional) If you are using the pressure-based solver and you do not want to include species diffusion effects in the energy equation, turn off the Diffusion Energy Source option. See Section  14.2.2 for details.

(e)   (optional, but recommended for CVD) If you want to model full multicomponent diffusion or thermal diffusion, turn on 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  14.1.4.)

Define $\rightarrow$ Materials...

Mixture properties include the following:

  • species in the mixture

  • reactions

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

figure   

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

Note that if you were modeling the silicon deposition reactions in the example in Section  14.2.1, you would need to include both Si species (gas and solid) in the mixture.

figure   

Note that the final gas phase species named in the Selected Species list should be the carrier gas if your model includes species in dilute mixtures. (This is because FLUENT will not solve the transport equation for the final species.) Note also that any reordering, adding or deleting of species should be handled with caution, as described in Section  14.1.4.

3.   Check and/or set the properties of the individual species in the mixture. (See Section  14.1.4.) Note that if you are modeling the heat of surface reactions, you should be sure to check (or define) the formation enthalpy for each species.

4.   Set species boundary conditions.

Define $\rightarrow$ Boundary Conditions...

In addition to the boundary conditions described in Section  14.1.5, 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, turn on the Reaction option in the Species section of the Wall panel.

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If you have enabled the global Low-Pressure Boundary Slip option in the Viscous Model panel, 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 panel.

See Section  7.13.1 for details about boundary condition inputs for walls. See Section  7.19.6 for details about boundary condition inputs for porous media.


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