This node adds several conditions for temperature exchange at the interfaces of an isothermal domain. It can be applied on interior and exterior boundaries of the computational domain, except on the boundaries found inside a single isothermal domain.

In addition to the default Isothermal domain Interface node always present when the Isothermal domain check box is selected under Physical Model section, you can add more Isothermal domain Interface nodes if needed.

This section is available when temperature-dependent material properties are used. By default the temperature of the parent interface is used and the section is not editable. To edit the Temperature field, click Make All Model Inputs Editable (). The available options are User defined (default), Common model input (the minput.T variable, set to 293.15 K by default) and all temperature variables from the physics interfaces included in the model. To edit the minput.T variable, click the Go to Source button (), and in the Default Model Inputs node under Global Definitions, set a value for the Temperature in the Expression for remaining selection section.

If this node is selected from the Pairs menu, choose the pair on which to apply this condition. A pair has to be created first. See Identity and Contact Pairs in the COMSOL Multiphysics Reference Manual for more details.

The available Interface type options are Thermal insulation (the default), Continuity, Ventilation, Convective heat flux, and Thermal contact. Depending on the Interface type selected from the list, further settings are required.

The available Flow direction options are Positive normal direction (the default), Negative normal direction, and Both sides. For each option, either the Mass flux or the Mass flow rate should be specified:

The External temperature found under the section of the same name must be set when the isothermal domain interface is also an exterior boundary.

Either the Heat transfer coefficient h or the Thermal conductance hth should be specified.

When the Heat transfer coefficient h option is selected, the default option is to enter a User defined value for the Heat transfer coefficient h.

In addition, the following options are also available to control the type of convective heat flux to model: External natural convection, Internal natural convection, External forced convection, or Internal forced convection. A complete description of these options can be found in Heat Flux, Convective Heat Flux.

The External temperature found under the section of the same name must be set when the isothermal domain interface is also an exterior boundary.

Either specify the Surface thermal resistance, Rt,s (SI unit: K·m2/W), or set the Thermal resistance, Rt (SI unit: K/W) and evaluate Rt,s from it:

where A (SI unit: m2) is the surface area of the boundary.

The External temperature found under the section of the same name must be set when the isothermal domain interface is also an exterior boundary.

This section is not available if the Interface type is set to Thermal Insulation or Continuity. Else, the External temperature, Text should be specified. It is used to compute the heat exchange with the exterior by the Ventilation, Convective heat flux, and Thermal contact options on isothermal domain interfaces that are also exterior boundaries. The value is ignored on interior boundaries.

For User defined, enter a value or expression for the Temperature Text. Else, select an Ambient temperature defined in an Ambient Properties node under Definitions.

Select Opaque (the default) or Transparent to set the interface’s opacity type.

This is needed when the interface contributes with any boundary condition from the Radiation menu. It picks the side where irradiation starts from.

If the Isothermal domain check box is selected under the Physical Model section:

Physics Tab with interface as Heat Transfer in Solids and Fluids, Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media, Heat Transfer in Building Materials or Bioheat Transfer selected: