Thermal Connection, Interface-Interface
Use this node to connect the interfaces of two boundary selections by a thermal resistor, thermal capacitor or Lumped Thermal System interface.
Boundary Selection, Connector 1
Select the boundaries corresponding to the first connector.
Boundary Selection, Connector 2
Select the boundaries corresponding to the second connector.
The selections are only applicable on boundaries with Layer type set to General in the Thin Layer (Heat Transfer Interface) and Solid (Heat Transfer in Shells Interface), Thin Film (Heat Transfer Interface) and Fluid (Heat Transfer in Shells Interface), and Fracture (Heat Transfer Interface) and Porous Medium (Heat Transfer in Shells Interface) features. In addition, the layered material applied on the boundaries must correspond to the one set in the Shell Properties section.
Shell Properties
Set the layered material on which each connector can be applied.
Interface Selection
Set the interfaces for which each connector should be applied. The available options in the Connector 1, apply to and Connector 2, apply to list are Top interface (default), Bottom interface, and Exterior interfaces. The later is not available when both connectors share a boundary and the same layered material defined in the Shell properties section.
•
For a general description of layer and interface selections, see Layer and Interface Selection Tools.
•
You can provide material parameters with a through-thickness variation by using expressions containing the extra dimension coordinate as described in Using the Extra Dimension Coordinates.
The desired selection for the node may correspond to boundaries with different layered materials.
See Layered Material, Layered Material Link, Layered Material Stack, Layered Material Link (Subnode), and Single Layer Materials in the COMSOL Multiphysics Reference Manual.
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.
See Tangent and Normal Variables in the COMSOL Multiphysics Reference Manual.
Thermal connection
Select the Connection type from the list: Conductive thermal resistor (default), Thermal capacitor, or Lumped thermal system.
Conductive Thermal Resistor
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.
•
When Specify is Thermal resistance (default), enter directly a value or expression for R.
•
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:
•
Plane shell (default): set values or expressions for the surface Area A and the Thickness L of the plane. The thermal resistance is then defined as
•
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
•
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 checkbox 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 Convectively Enhanced Conductivity section that appears underneath.
For all Configuration options, select the Optically thick participating medium checkbox to take into account 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 checkbox is selected in the Thermal Connection 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:
•
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 more details on the required parameters.
•
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 more details on the required parameters. By default, the Thickness value set in the Thermal Connection section for L is used for the Plate distance.
•
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 between the connectors 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 calculate the Nusselt number. When the properties are taken From material, 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
Optically Thick Participating Medium
 
This section is available when the Optically thick participating medium checkbox is selected in the Thermal Connection 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 From material, the material selected in the Thermal Connection section is used. If the material properties are temperature-dependent, they are evaluated at the average temperature of the connector.
Thermal Capacitor
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 Specify list, different settings are required:
•
With Thermal capacitance (default), set directly a value or expression for C.
•
With Density and heat capacity, set values or expressions for the Volume, V, the Density, ρ, and the Heat capacity at constant pressure, Cp. Select any material from the Material list to define the properties From material. For User defined enter values or expressions.
•
With Mass and heat capacity, set values or expressions for the Mass, m, and the Heat capacity at constant pressure, Cp. Select any material from the Material list to define Cp From material. For User defined enter a value or expression.
Lumped Thermal System
It models a thermal network defined by a Lumped Thermal System 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 External Terminal feature in the Source 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 External Terminal feature for a transient simulation.
When the Isothermal terminal checkbox 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 checkbox 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, Interface feature.
Theory for Thermal Connection
Lumped Composite Thermal Barrier with Shells: Application Library path Heat_Transfer_Module/Tutorials,_Thin_Structure/lumped_composite_thermal_barrier_shells
Location in User Interface
Context Menus
Heat Transfer in Shells > Thermal Connection, Interface-Interface
Heat Transfer in Films > Thermal Connection, Interface-Interface
Heat Transfer in Fractures > Thermal Connection, Interface-Interface
Ribbon
Physics tab with Heat Transfer in Shells or any version of the Heat Transfer in Thin Structures interface selected:
Global > Thermal Connection, Interface-Interface