Open Boundary

Use this condition to define a boundary as the limit between a non-solid domain of the geometry and the rest of the same fluid domain that is not represented in the geometry. At the open boundary both inflow and outflow conditions are supported.

For an outgoing fluid flow across the boundary, it applies a zero conductive flux condition:

(6-17)

For an incoming flow of velocity field u across the boundary, it accounts by default for the heat flux induced by the flow rate through a Danckwerts condition on the enthalpy:

(6-18)

where ΔH is the sensible enthalpy. See Theory for the Inflow Boundary Condition for more details on the Danckwerts condition and the definition of ΔH.

Alternatively the open boundary condition can set a constraint on the temperature for an incoming flow

(6-19)

Both conditions are based on the knowledge of the upstream temperature at the outer boundary of the virtual domain, but the first one should be preferred to take into account the feedback of the model heat sources and temperature constraints on the inlet temperature profile.

Upstream Properties

Enter the Tustr outside the open boundary. For , enter a value or expression. Else, select any available input (like an defined in an node under ).

Inflow condition

Unfold this section to change the inflow condition:

•

The condition (default) prescribes the flux defined from the upstream temperature and the fluid velocity at the boundary. Using this condition the temperature 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 temperature and upstream temperature.

•

The option enforces the upstream temperature on the boundary.


	Natural Convection Cooling of a Vacuum Flask: Application Library path Heat_Transfer_Module/Tutorials,_Forced_and_Natural_Convection/vacuum_flask

Location in User Interface

Context Menus

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Physics tab with interface as , or any version of the Heat Transfer interface selected:

Physics tab with selected in the model tree: