COMSOL 6.2 - Thermal Connection

Select the from the list: (default), , or .

It models heat loss by conduction in a domain by a thermal resistance R (SI unit: K/W) between the two connectors. This resistance may be defined depending on thermal and geometric properties, and may take into account convection and radiation in optically thick participating medium.

See Theory for Thermal Connection for more details on the underlying theory.

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When is (default), enter directly a value or expression for R.

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When is , further settings display underneath to define the thermal resistance depending on the thermal conductivity and the geometric configuration.

Select any material from the list to define the k . For enter a value or expression.

Select a among the following options, and set the needed geometric properties:

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(default): set values or expressions for the surface A and the L of the plane. The thermal resistance is then defined as

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: set values or expressions for the ri, the ro, and the H of the cylinder. The thermal resistance is then defined as

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: set values or expressions for the ri and the ro of the sphere. The thermal resistance is then defined as

When the is , select the check box to take into account convective heat flux by enhancing the thermal conductivity according to the Nusselt number. Further settings (see below) are then required in the section that appears underneath.

For all options, select the check box to take into account radiation in a medium with high optical thickness. Further settings (see below) are then required in the section that appears underneath.

This section is available when the check box is selected in the section. Convection is accounted for by multiplying the thermal conductivity by the Nusselt number.

The following options are available in the list:

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, for which values for the H and the ΔT should be specified for the computation of the Nusselt number. Unfold the section for more details on the required parameters.

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, for which values for the H, the L, and the ΔT should be specified for the computation of the Nusselt number. Unfold the section for more details on the required parameters. By default, the set in the section for L is used for the .

For the two first options, select (default) or to define the ΔT. When is selected the temperature difference between the connectors is used.

Select a between and , and depending on the selected option, set values or expressions for the material properties needed to calculate the Nusselt number. When the properties are taken , the material selected is used. If the material properties are temperature-dependent, they are evaluated at the average temperature of the connectors.

	Equivalent Thermal Conductivity Correlations

This section is available when the check box is selected in the section. It defines the properties of the participating medium to model the heating due to the propagation of the rays by modifying the thermal conductivity with

where nr is the refractive index (dimensionless), σ is the Stefan-Boltzmann constant (SI unit: W/(m2·K4)), Tavg is the average temperature of the connector and βR is the extinction coefficient. The settings are the same as for the Optically Thick Participating Medium feature.

When the properties are taken , the material selected in the section is used. If the material properties are temperature-dependent, they are evaluated at the average temperature of the connector.

It models heat storage in a domain with a thermal capacitance C (SI unit: J/K) between the two connectors.

For a steady-state problem the temperature difference does not change with time and the imposed heat flux simplifies to zero.

See Theory for Thermal Connection for more details on the underlying theory.

Depending on the option selected in the list, different settings are required:

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With (default), set directly a value or expression for C.

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With , set values or expressions for the , V, the , ρ, and the , Cp. Select any material from the list to define the properties . For enter values or expressions.

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With , set values or expressions for the , m, and the , Cp. Select any material from the list to define Cp . For enter a value or expression.

It models a thermal network defined by a interface between the two connectors.

The average temperature on the selected boundaries for each connector can be prescribed at a node of the thermal network where an External Terminal feature of The Lumped Thermal System Interface is applied.

In return, the heat rate defined at the node of the thermal network is applied on the selected boundaries of each connector.

For each connector, select an feature in the list to define which node of the thermal network provides the heat rate Pext to be prescribed on the boundary. The initial temperature of the connector is also taken from the selected feature for a transient simulation.

When the check box is not selected (default), the average temperature on the boundaries is constrained to the temperature at the terminal node of the thermal network. Select this check box to apply the constraint on the space-dependent temperature instead, which corresponds to a stronger constraint.

	When only one External Terminal feature is selected in Connector 1 or Connector 2, the behavior is equivalent to the Lumped System Connector feature.

	Theory for Thermal Connection

	Lumped Composite Thermal Barrier: Application Library path Heat_Transfer_Module/Tutorials,_Thin_Structure/lumped_composite_thermal_barrier

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