Thermal Contact

This node defines correlations for the conductance h at the interface of two bodies in contact. It can be added to pairs by selecting from the menu. Note that in this case the source term is applied on the destination side.

The conductance h is involved in the heat flux across the surfaces in contact according to:

where u and d subscripts refer to the upside and downside of the slit, respectively. should be activated on a or on a where a structural mechanics physics interface defines a contact pair feature.

Pair Selection

If this node is selected from the 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.

Model Input

This section has fields and values that are inputs to expressions that define material properties. If such user-defined property groups are added, the model inputs appear here.

Temperature

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 field, click (

). The available options are (default), (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 button (

), and in the node under , set a value for the in the section.

Material Type

Select an option in the list to specify if the inputs of the section are defined in the material or spatial frame:

•

The default option for the node is , which specifies that the heat source Qb is defined in the material frame. Because the heat transfer variables and equations are defined in the spatial frame, the inputs are internally converted to the spatial frame. See Conversion Between Material and Spatial Frames for details.

•

The option defines Qb in the spatial frame. No frame conversion is needed.

•

The option uses the option selected in the list of the section of the material applied on the boundary on which the node is active.


	This option has no effect when the component does not contain a moving frame because the material and spatial frames are identical in such cases. With a Deformed Geometry or a Moving Mesh interface, the heat transfer features automatically account for deformation effects of the material and spatial frames on heat transfer properties. In particular the effects of volume changes on the density are considered. See Handling Frames in Heat Transfer and Material and Spatial Frames for details.

Thermal Contact

Select a : (the default), or .

With the model, you consider the microscopic configuration of the joint, by setting both the constriction conductance at the contact spots, hc, and the gap conductance due to the fluid in the interstitial space, hg, to evaluate the joint conductance. The characteristic size of the microscopic surface asperities, and both the conductance of constriction and gap need to be specified.

To represent the surfaces asperities and the fluid gap in-between these surfaces by an equivalent thin layer, select the option instead.

The radiative conductance can be accounted for with the two contact models. It should be considered at high temperatures, above 600°C.

See Theory for Thermal Contact for details.

Depending on the selected , further settings display underneath.

Constriction Conductance with interstitial gas

Select a : (the default), , or . For enter a value or expression for hc.

Then select the : (the default) or (availableif or is selected as the ). For enter a value for hg.

Equivalent thin resistive layer

The available options to specify the resistive behavior of the equivalent layer are (the default), , and . Depending on the selected option, enter values or expressions for the , Req, the , heq, the , keq, and the , ds.

Radiative conductance

Finally, choose the : (the default) or . For enter a value for hr.

Contact Surface Properties

This section is available when the is , if or are chosen as the for the . Enter values for the:

•

σasp

•

masp

•

For select a : (the default), , or .

•

For enter a value for Hc.

•

For enter a value for the c1 and c2.

•

For enter a value for HB. It should be between 1.30 and 7.60 GPa.

For select a Econtact: (the default) or .

•

For , enter values or expressions for the , Eu, the , Ed, the , νu, and the , νd. If this node is selected from the menu, enter instead values or expressions for the , Esrc, the , Edst, the , νsrc, and the , νdst.

•

For enter another value or expression for Econtact.

Gap Properties

This section is available when the is , if is selected as the under .

The default kgap is taken . For select , , , or based on the characteristics of the gas thermal conductivity, and enter another value or expression.

Also enter the following:

•

pgap

•

Radiative Conductance

This section is available when is selected as the under .

By default the ε is taken . For enter another value or expression.

Thermal Friction

Select a r: (the default) or . For enter a value for r.

Select either the (the default) or .

•

For enter a frictional heat source Qb.

•

For enter the heat rate Pb.


	Theory for Thermal Contact


	Upside and downside settings can be visualized by plotting the global normal vector (nx, ny, nz), that always points from downside to upside. Note that the normal vector (ht.nx, ht.ny, ht.nz) may be oriented differently. In addition, surface plots for the temperatures on the upside (ht.Tu) and downside (ht.Td) of the slit are automatically generated in 3D components. See Tangent and Normal Variables in the COMSOL Multiphysics Reference Manual.


	Thermal Contact Resistance Between an Electronic Package and a Heat Sink: Application Library path Heat_Transfer_Module/Thermal_Contact_and_Friction/thermal_contact_electronic_package_heat_sink

Location in User Interface

Context menus

Ribbon

Physics Tab with interface as , , , , or selected:
interface