In the standard dsmcFoam solver (OF 2.4.0), the wallInteractionModel is a global parameter.
Which means each part of the wall uses the same wall interaction model. The diffusive fraction is the same everywhere.
In this project, a new wall interaction model is defined, called "VarMixedDiffuseSpecular".
It allow us to use a diffusive fraction variable associate with each wall patch.
To specify the diffusive fraction parameters, we use the alphaFixedValued type boundary type for the wall temperature boundary condition.