Use this node to model inflow of water vapor through a virtual domain, at inlet boundaries of moist air and hygroscopic porous medium domains. The upstream moisture conditions (either vapor concentration custr, or vapor mass fraction ωustr, or relative humidity ϕw,ustr and temperature Tustr) are known at the outer boundary of the virtual domain. The inflow condition is often similar to a moisture content condition. However using this condition the upstream vapor concentration is not strictly enforced at the inlet. The higher the flow rate, the smallest difference between the inlet and upstream moisture content. In case of moisture sources or moisture constraints close to the inlet boundary, the inflow condition induces a moisture profile that approaches to the moisture profile that would be obtained by computing the solution in the virtual domain upstream the inlet.

If both inflow and outflow conditions are expected at some boundaries, use the Open Boundary feature instead.

When the Diluted species option is selected in the Mixture type for moist air list, this boundary condition estimates the moisture flux through the inlet boundary from a Danckwerts condition on the vapor concentration:

When the Concentrated species option is selected in the Mixture type for moist air list, this condition is rewritten as

to be expressed in function of the vapor mass fraction ωv, with

This node can be applied on the exterior boundaries of a computational domain in which either a Moist Air (Moisture Transport Interface) node or an Hygroscopic Porous Medium node is active.

When Specify is set to Relative humidity in the Specify list, set both the Upstream temperature Tustr and the Upstream relative humidity ϕw,ustr from which the upstream vapor concentration and the vapor mass fraction can be defined:

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 a value or expression for the Upstream vapor concentration custr.

Finally, choose Vapor mass fraction in the Specify list to set a value or expression for the Upstream vapor mass fraction ωustr.

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