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 ϕw,0 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
The Constraint settings can be set to
Pointwise constraints (default),
Weak constraints or
Nitsche constraints. Select
Weak constraints to replace the standard constraints with a weak implementation. The
Nitsche constraints option ensures continuity of the diffusive flux.
) and select Advanced Physics Options in the Show More Options dialog box. 
