Overriding Mechanism for Heat Transfer Boundary Conditions

Many boundary conditions are available in heat transfer. Some of these can coexist (for example, Heat Flux and Thin Layer (Heat Transfer interface) and Solid (Heat Transfer in Shells interface)); others cannot (for example, Heat Flux and Thermal Insulation).

Several categories of boundary condition exist in heat transfer. Table 3-3 gives the overriding rules for these groups.

Temperature, Open Boundary, Open Boundary, Inflow

Thermal Insulation, Symmetry (Heat Transfer interface), Periodic Condition (Heat Transfer interface)

Heat Flux

Boundary Heat Source, Radiation Group (Surface-to-Surface Radiation Interface), Line Heat Source on Axis

Thin Layer (Heat Transfer interface) and Solid (Heat Transfer in Shells interface), Thermal Contact, Thin Film (Heat Transfer interface) and Fluid (Heat Transfer in Shells interface), and Fracture (Heat Transfer interface) and Porous Medium (Heat Transfer in Shells interface)

Isothermal Domain Interface

Table 3-3: Overriding Rules for Heat Transfer Boundary conditions
A\B	1	2	3	4	5	6
1-Temperature	X	X			X
2-Thermal Insulation	X	X
3-Heat Flux	X	X
4-Boundary heat source
5-Thin Layer	X				X
6-Isothermal Domain Interface						X

When there is a boundary condition A above a boundary condition B in the model tree and both conditions apply to the same boundary, use Table 3-3 to determine if A is overridden by B or not:

•

Locate the line that corresponds to the A group (see above the definition of the groups). In the table above only the first member of the group is displayed.

•

Locate the column that corresponds to the group of B.

•

If the corresponding cell is empty, A and B contribute. If it contains an X, B overrides A.


	Group 3 and group 4 boundary conditions are always contributing. That means that they never override any other boundary condition. But they might be overridden.

Example

Consider a boundary where is applied. Then a boundary condition is applied on the same boundary afterward.

•

belongs to group 3.

•

belongs to group 2.

•

The cell on the line of group 3 and the column of group 2 contains an X so is overridden by .

This mechanism can be checked on the COMSOL Desktop, in the section of each feature, as shown in the following table:

Table 3-4: Override and Contribution sections
Heat Flux	Symmetry


	In the example above, if Symmetry followed by Heat Flux is added, the boundary conditions contribute.