Open Boundary
Use this condition to define a boundary as the limit between a moist air (or hygroscopic porous medium) domain of the geometry and the rest of the same moist air (or hygroscopic porous medium) domain that is not represented in the geometry.
This node can be applied on the exterior boundaries of a computational domain in which either a Moist Air (Moisture Transport Interface) node or a Hygroscopic Porous Medium node is active.
At the open boundary both inflow and outflow conditions are supported. Use the Inflow and Outflow features on boundaries where only inflow or outflow conditions are expected.
For an outgoing moist airflow across the boundary, it applies a zero diffusive flux condition:
(7-5)
For an incoming flow of velocity field u across the boundary, it accounts by default for the moisture flux induced by the flow rate. When the Diluted species option is selected in the Mixture type for moist air list, this is done through 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 mass fraction ωv, with
Note that on the exterior boundaries of a porous medium, the Danckwerts condition is always based on the vapor mass fraction, because the concentrated species formulation is always used for the moist air phase.
Alternatively the open boundary condition can set a constraint on the vapor concentration or mass fraction for an incoming flow, depending on the option is selected in the Mixture type for moist air list:
(7-6)
(7-7)
Both types of conditions are based on the knowledge of the upstream moisture content (from the vapor concentration, the vapor mass fraction, or the relative humidity and the temperature) at the outer boundary of the virtual domain, but the concentration and mass fraction ones should be preferred to account for the feedback of the model moisture sources and moisture constraints on the inlet moisture profile.
Upstream Properties
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 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.
Inflow Condition
Unfold this section to change the inflow condition:
The Flux (Danckwerts) condition (default) prescribes the flux defined from the upstream vapor concentration (or mass fraction) and the fluid velocity at the boundary. Using this condition, the moisture condition is not strictly enforced at the inlet. Instead a flux is set on this boundary. The higher the flow rate, the smallest difference between the inlet and upstream vapor concentration (or mass fraction).
The Nitsche constraints option enforces the upstream vapor concentration (for Diluted species option) or the upstream vapor mass fraction (for Concentrated species option) on the boundary.
Evaporative Cooling of Water: Application Library path Heat_Transfer_Module/Phase_Change/evaporative_cooling
Condensation Detection in an Electronic Device with Transport and Diffusion: Application Library path Heat_Transfer_Module/Power_Electronics_and_Electronic_Cooling/condensation_electronic_device_transport_diffusion
Location in User Interface
Context Menus
Ribbon
Physics Tab with interface as Moisture Transport in Air, Moisture Transport in Building Materials, or Moisture Transport in Porous Media selected: