The mass flux of vapor is computed with Darcy’s law. Set the Relative moist air permeability, κrm (dimensionless), that multiplies the permeability in the Darcy’s law to account for the saturation of the moist air phase.

Set the Vapor diffusion coefficient Dv (SI unit: m2/s) for the diffusion of vapor in air. The default value 2.6·10−5 m²/s is valid at T = 298 K and pmA = 1 atm. You may set a temperature or pressure-dependent diffusion coefficient through the use of the variables mts.T and mts.pmA.

Specify the Effective diffusivity model used to account for the porosity and the tortuosity in the effective diffusion coefficient, Deff (SI unit: m2/s). The available options are Millington and Quirk model (the default), Bruggeman model, Tortuosity model, and No correction.

For the Tortuosity model option, enter a value for the Tortuosity factor τ (dimensionless). The default is 1.