If this node is selected from the Pairs menu, choose the pair on which to apply this condition. A pair has to be created first. See Identity and Contact Pairs in the COMSOL Multiphysics Reference Manual for more details.

When Specify is set to Relative humidity, the equation for this condition is

where and T0 are the prescribed relative humidity and temperature on the boundary. For User Defined, enter values or expressions. Else, select any available input (like Ambient temperature defined in an Ambient Properties node under Definitions). If the Concentrated species formulation is used, the vapor mass fraction is then defined as:

Alternatively, choose Vapor concentration in the Specify list and set directly the Vapor concentration c0. If the Concentrated species formulation is used, the vapor mass fraction is then defined as:

Finally, choose Vapor mass fraction in the Specify list to set directly ω0. If the Diluted species formulation is used, the vapor concentration is then defined as:

To display this section, click the Show More Options button () and select Advanced Physics Options. Select the Use weak constraints check box to replace the standard constraints with a weak implementation.

The Discontinuous Galerkin constraints option ensures continuity of the diffusive flux.

Physics Tab with interface as Moisture Transport in Air, Moisture Transport in Building Materials, or Moisture Transport in Porous Media selected: