Conductive Thermal Resistor
This feature models a two-port passive component of the thermal system. It connects two nodes, by creating a difference in the temperatures of its two connecting ports. It models heat loss by conduction in a domain.
It adds equations for the heat rates Pp1 and Pp2 and the temperatures Tp1 and Tp2 at the connecting ports p1 and p2 of the component, and defines the following relation between the heat rate P and the temperature difference ΔT:
where R (SI unit: K/W) is the thermal resistance, which may be defined depending on thermal and geometric properties, and may account for convection and radiation in optically thick participating medium.
See Theory for the Conductive Thermal Resistor Component for details about the underlying theory.
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.
By default the Temperature is User defined and the average of the two port temperatures, Tave = 0.5*(Tp1+Tp2), is set.
Identifier
Enter a Component name for the thermal resistor. The prefix is R.
Node Connections
Set the two Node names for the nodes connected by the thermal resistor.
Component Parameters
The thermal resistance used to express the heat rate P in function of the temperature difference ΔT should be defined in this section.
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When Specify is Thermal resistance, enter directly a value or expression for R.
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When Specify is Thermal and geometric properties, further settings display underneath to define the thermal resistance depending on the thermal conductivity and the geometric configuration.
Select any material from the Material list to define the Thermal conductivity k From material. For User defined enter a value or expression.
Select a Configuration among the following options, and set the needed geometric properties:
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Plane shell (the default): set values or expressions for the surface Area A and the Thickness L of the plane. The thermal resistance is then defined as
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Cylindrical shell: set values or expressions for the Inner radius ri, the Outer radius ro, and the Height H of the cylinder. The thermal resistance is then defined as
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Spherical shell: set values or expressions for the Inner radius ri and the Outer radius ro of the sphere. The thermal resistance is then defined as
When the Configuration is Plane shell, select the Convectively enhanced conductivity check box to account for convective heat flux by enhancing the thermal conductivity according to the Nusselt number. Further settings (see below) are then required in the Convectively Enhanced Conductivity section that appears underneath.
For all Configuration options, select the Optically thick participating medium check box to account for radiation in a medium with high optical thickness. Further settings (see below) are then required in the Optically Thick Participating Medium section that appears underneath.
Convectively Enhanced Conductivity
This section is available when the Convectively enhanced conductivity check box is selected in the Component Parameters section. Convection is accounted for by multiplying the thermal conductivity by the Nusselt number.
The following options are available in the Nusselt number correlation list:
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Horizontal cavity heated from below, for which values for the Cavity height H and the Temperature difference ΔT should be specified for the computation of the Nusselt number. Unfold the Sketch section for details about the required parameters.
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Vertical rectangular cavity, for which values for the Cavity height H, the Plate distance L, and the Temperature difference ΔT should be specified for the computation of the Nusselt number. Unfold the Sketch section for details about the required parameters. By default, the Thickness value set in the Component Parameters section for L is used for the Plate distance.
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User defined, for which a value for Nu should be specified directly.
For the two first options, select Automatic (default) or User defined to define the Temperature difference ΔT. When Automatic is selected the temperature difference across the component is used.
Select a Fluid type between Gas/Liquid and Ideal gas, and depending on the selected option, set values or expressions for the material properties needed to compute the Nusselt number. When the properties are taken From material, the material selected in the Component Parameters section is used. If the material properties are temperature-dependent, they are evaluated at the average temperature in the component, Tave = 0.5*(Tp1+Tp2).
Equivalent Thermal Conductivity Correlations
Optically Thick Participating Medium
This section is available when the Optically thick participating medium check box is selected in the Component Parameters 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), σs is the Stefan-Boltzmann constant (SI unit: W/(m2·K4)), and βR is the extinction coefficient. The settings are the same as for the Optically Thick Participating Medium feature.
When the properties are taken From material, the material selected in the Component Parameters section is used. If the material properties are temperature-dependent, they are evaluated at the average temperature in the component, Tave = 0.5*(Tp1+Tp2).
Results
Select appropriate options in the Add the following to default results in order to include the following global variables (space-independent) in the default plots:
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  Heat rate
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Temperature at node 1
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 Temperature at node 2
Composite Thermal Barrier, Lumped Thermal System: Application Library path Heat_Transfer_Module/Tutorials,_Thin_Structure/lumped_composite_thermal_barrier
Location in User Interface
Context Menus
Lumped Thermal System>Conductive Thermal Resistor
Ribbon
Physics Tab with Lumped Thermal System selected:
Global>Conductive Thermal Resistor