Diffuse Flux
The Diffuse Flux boundary condition sets the molecular flux emitted from the boundary to a user-specified value. This boundary condition applies only in the molecular flow limit (Knudsen number, Kn > 10). 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 as number of SCCMs. The flux is assumed to be emitted from a stationary boundary.
Diffuse Flux
Select the Boundary condition: Directly (the default), Number of SCCM units, Mass flux, or Total mass flow.
Directly
For Directly enter a value or expression for the Molecular flux Jo (SI unit: 1/(m2·s)). The default is 0 (1/(m2·s)).
Number of SCCM (standard cubic centimeters per minute) Units
For Number of SCCM units enter the Number of SCCM units Qsccm (dimensionless), and this quantity is automatically converted to a standardized volumetric flow rate in SI units. Select an option from the Standard flow rate defined by list — Standard density (the default) or Standard pressure and temperature.
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For Standard density enter a Standard molar volume Vm (SI unit: m3/mol). The default is 0.0224136 m3/mol.
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For Standard pressure and temperature enter a Standard pressure Pst (SI unit: Pa) and Standard temperature Tst (SI unit: K). The defaults are 1 atm and 273.15 K, respectively.
 
For 2D components, also enter a Channel thickness dbc (SI unit: m).
Mass Flux
For Mass flux enter a value or expression for the Mass flux Mf (SI unit: kg/(m2·s)).
Total Mass Flow
For Total mass flow enter a value or expression for the Total mass flow Qm (SI unit: kg/s).