This node is active by default on all the interior and exterior boundaries of the computational domain, adjacent to domains where a Hygroscopic Porous Medium node is applied with Equilibrium between liquid and gas phases set to Nonequilibrium formulation. It shows which boundaries are adjacent to domains where both the relative humidity ϕw and the liquid water saturation sl are solved.

On these boundaries, the conditions available at the physics interface level are not applicable, because they define conditions which either act only on the relative humidity, or also have an effect on the liquid water saturation. In the first case, this can be done adding the conditions to the Moist Air (Hygroscopic Porous Medium) subnode, and the second case is not allowed because conditions on liquid water saturation should be handled by the Liquid Water (Hygroscopic Porous Medium) subnode and its children. There is however one exception on interior boundaries: Porous Interface.

Concerning the domain conditions, the Moisture Source and Initial Values nodes, available at the physics interface level, are not applicable in the domains delimited by the Nonequilibrium Boundary condition.