Flux Matching
Flux matching must be performed for each species in order for the total molar mass in the system to be conserved. If a model also contains a physics interface to compute the fluid velocity and pressure (the Laminar Flow interface for example) and the gas temperature (the Heat Transfer in Fluids interface for example) then those physics interfaces require appropriate flux matching boundary conditions. The Heavy Species Transport interface automatically computes flux matching variables for the total mass flux and heat source of reaction on surfaces.
Surface Chemistry Tutorial Using the Plasma Module: Application Library path Plasma_Module/Chemical_Vapor_Deposition/surface_chemistry_tutorial
flux matching for each Species
The inward mass flux for species k on a reacting surface is given by:
(5-22)
This is the natural boundary condition for Equation 5-4 and results in either an inward or outward mass flux for species k, depending on the surface chemical mechanism stoichiometry. If the species is an ion, then there is an additional flux contribution due to migration. In this case, Equation 5-22 becomes:
This additional flux contribution ensures that when the normal electric field is directed to the wall, there is an outflux of ions due to migration.
flux matching for the total mass flux
If a model contains the Laminar Flow interface, an expression for the mass averaged velocity is needed on reacting surfaces. The Heavy Species Transport interface creates an appropriate variable for the inward mass flux, which can be accepted as a feature input for the Mass Flow option in the Inlet boundary condition of the Laminar Flow interface.
The inward mass flux, Mf is defined as:
where Rsurf,k is the surface rate expression for each species which comes from summing the surface reaction rates multiplied by their stoichiometric coefficients over all surface reactions:
.
flux matching for the total HEAT flux
If a model contains the Heat Transfer in Fluids interface, an expression for the total heat source of reactions is needed. The Heavy Species Transport interface creates an appropriate variable for the total heat source of reactions, which can be accepted as a feature input in the Reaction Heat Flux boundary condition of the Heat Transfer in Fluids interface.
The total heat source due to reactions is defined as:
where hi is the molar enthalpy change due to reaction i. Depending on the surface chemical mechanism stoichiometry, this can either cause heating (exothermic) or cooling (endothermic).