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).

Alternatively, choose Vapor concentration in the Specify list and set directly the Vapor concentration c0.

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.

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