The Diffuse Flux boundary condition sets the molecular flux emitted from the boundary to a user-specified value. The flux is emitted according to Knudsen’s law (the emitted flux in a given direction is proportional to the cosine of its angle to the surface normal). This can be set directly as a flux, as a total incoming mass flow, or number of SCCMs.

Select the Outgoing flux: Specify directly (the default), Number of SCCM units, Mass flux, or Total mass flow. The rest of the settings are the same as for Wall, described in the Flux section.