Thermal Contact
This node defines correlations for the conductance h at the interface of two bodies in contact. It can be added to internal boundaries by selecting Thermal Contact from the Thin Structure menu or to pairs by selecting Thermal Contact from the Pairs 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. Pair version of Thermal Contact should be activated on a Identity Pair or on a Contact Pair where a structural mechanics physics interface defines a contact pair feature.
Pair Selection
If this node is selected from the Pairs menu, choose the pair to apply this condition to. A pair must be created first. See Identity and Contact Pairs in the COMSOL Multiphysics Reference Manual for more details.
Model Input
This section contains fields and values that are inputs for expressions defining material properties. If such user-defined property groups are added, the model inputs appear here.
Temperature
This section is available when material properties are temperature-dependent. 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.
Material Type
Select an option in the Material type list to specify if the inputs of the Thermal Friction section are defined in the material or spatial frame:
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The default option for the Thermal Contact node is Solid, 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.
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The Nonsolid option defines Qb in the spatial frame. No frame conversion is needed.
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The From material option uses the option selected in the Material type list of the Material Properties 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 take into account 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 Contact model: Constriction conductance with interstitial gas (default), or Equivalent thin resistive layer.
With the Constriction conductance with interstitial gas 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 between these surfaces by an equivalent thin layer, select the Equivalent thin resistive layer 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 Contact model, further settings display underneath.
Constriction Conductance with Interstitial Gas
Select a Constriction conductance: Cooper-Mikic-Yovanovich correlation (default), Mikic elastic correlation, or User defined. For User defined enter a value or expression for hc.
Then select the Gap conductance: User defined (default) or Parallel-plate gap gas conductance (available if Cooper-Mikic-Yovanovich correlation or Mikic elastic correlation is selected as the Constriction conductance). For User defined enter a value for hg.
Equivalent Thin Resistive Layer
The available options to specify the resistive behavior of the equivalent layer are Layer resistance (default), Layer conductance, and Layer thermal conductivity and thickness. Depending on the selected option, enter values or expressions for the Layer resistance, Req, the Layer conductance, heq, the Layer thermal conductivity, keq, the Layer thickness, ds, the Total resistance, Rtot, and the Total conductance, htot. The last two options define the resistive behavior of the equivalent layer independently of the contact area.
Radiative Conductance
Finally, choose the Radiative conductance: User defined (default) or Gray-diffuse parallel surfaces. For User defined enter a value for hr.
Contact Surface Properties
This section is available when the Contact model is Constriction conductance with interstitial gas, if Cooper-Mikic-Yovanovich correlation or Mikic elastic correlation are chosen as the Constriction conductance correlation for the Constriction conductance. Enter values for the:
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Surface roughness, asperities average height σasp
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Surface roughness, asperities average slope masp
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Contact pressure p
For Cooper-Mikic-Yovanovich correlation select a Hardness definition: Microhardness (default), Vickers hardness, or Brinell hardness.
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For Microhardness enter a value for Hc.
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For Vickers hardness enter a value for the Vickers correlation coefficient c1 and Vickers size index c2.
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For Brinell hardness enter a value for HB. It should be between 1.30 and 7.60 GPa.
For Mikic elastic correlation select a Contact interface Young’s modulus Econtact: Weighted harmonic mean (default) or User defined.
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For Weighted harmonic mean, enter values or expressions for the Young’s modulus, upside, Eu, the Young’s modulus, downside, Ed, the Poisson’s ratio, upside, νu, and the Poisson’s ratio, downside, νd. If this node is selected from the Pairs menu, enter instead values or expressions for the Young’s modulus, source, Esrc, the Young’s modulus, destination, Edst, the Poisson’s ratio, source, νsrc, and the Poisson’s ratio, destination, νdst.
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For User defined enter another value or expression for Econtact.
Gap Properties
This section is available when the Contact model is Constriction conductance with interstitial gas, if Parallel-plate gap gas conductance is selected as the Gap conductance correlation under Thermal Contact.
The default Gas thermal conductivity kgap is taken From material. For User defined select Isotropic, Diagonal, Symmetric, or Full based on the characteristics of the gas thermal conductivity, and enter another value or expression.
Also enter the following:
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Gas pressure pgap
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Gas thermal accommodation parameter α
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Gas fluid parameter β
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Gas particles diameter D
Radiative Conductance
This section is available when Gray-diffuse parallel surfaces is selected as the Radiative conductance correlation under Thermal Contact.
By default the Surface emissivity ε is taken From material. For User defined enter another value or expression.
Thermal Friction
Select a Heat partition coefficient r: Charron’s relation (default) or User defined. For User defined enter a value for r.
Select either the General source (default) or Heat rate.
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For General source enter a frictional heat source Qb.
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For Heat rate 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
Heat Transfer in Solids and Fluids>Thin Structures>Thermal Contact
Heat Transfer in Solids>Thin Structures>Thermal Contact
Heat Transfer in Fluids>Thin Structures>Thermal Contact
Heat Transfer in Porous Media>Thin Structures>Thermal Contact
Bioheat Transfer>Thin Structures>Thermal Contact
Heat Transfer in Solids>Pairs>Thermal Contact
Heat Transfer in Fluids>Pairs>Thermal Contact
Heat Transfer in Porous Media>Pairs>Thermal Contact
Bioheat Transfer>Pairs>Thermal Contact
Ribbon
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:
Pairs>interface>Thermal Contact