Thin Layer (Heat Transfer Interface) and Solid (Heat Transfer in Shells Interface)
These nodes define the thermal conductivity and thermodynamics properties of a material located on internal or external boundaries. The Thin Layer node is available under the Heat Transfer interface, while the Solid node is available under the Heat Transfer in Shells interface.
The material can be formed of one or more layers, and different conductive behaviors can be modeled through the setting of the Layer type:
•
Select Thermally thick approximation to model a layer that is a bad thermal conductor compared to the adjacent geometry. In this case, the tangential heat flux is neglected and only the heat flux across the layer’s thickness is considered. The layer can be constituted of multiple sub-layers with specific thickness and thermal properties. Each sub-layer can be distinguished when a heat source is applied to the layer. This option may also be used to enforce consistent initial conditions.
•
Select Thermally thin approximation to model a layer that is a good thermal conductor compared to the adjacent geometry. In this case, the temperature difference and heat flux across the layer’s thickness are neglected. Only the tangential heat flux is considered. The sub-layers are not distinguished when a heat source is applied to the layer.
•
Select General to model a layer in which both the normal and tangential heat fluxes should be considered. The layer can be constituted of multiple sub-layers with specific thickness and thermal properties, and heat sources can be applied on a sub-layer selection, and on up and down sides of the layer.
Boundary Selection
When the Solid node is added manually in the Heat Transfer in Shells interface, and for the Thin Layer node, select the Restrict to layered boundaries check box to make the node applicable only if a layered material is defined on the boundary. If a layered material (Material with Layer thickness specified, Single Layer Material, Layered Material Link, or Layered Material Stack) is available, its name is then displayed beside the boundary index (for example, slmat1), otherwise the boundary is marked as not applicable.
When Solid is the default node of the Heat Transfer in Shells interface, it is applied on all boundaries where the Heat Transfer in Shells interface is applied, and neither the boundary selection nor the Restrict to layered boundaries check box are editable.
Note that when the Shell type is Nonlayered shell in the Shells Properties section of the parent interface or node, the Restrict to layered boundaries check box is not editable.
Shell Properties
Solid (Heat Transfer in Shells Interface)
Different settings are available, depending on the settings in the Shell Properties section of the parent interface, and whether Solid is the default node or was added manually:
•
When the Shell type is Layered shell in the Shells Properties section of the parent interface, the same layered material is used in the Solid node, but you can limit the contribution to individually selected layers by clearing the Use all layers check box, when the node was added manually. For a given Layered Material Link or Layered Material Stack, you get access to a list of check boxes for the selection of the individual layers. In this case, both the General and Thermally thin approximation options are available in the Layer Model section.
•
When the Shell type is Nonlayered shell in the Shells Properties section of the parent interface, the Thickness is taken From physics interface in the Solid node. This option is not editable when Solid is the default node, but you can change to User defined and override the interface’s setting with a specific value or expression for Lth when the node was added manually. In this case, only the Thermally thin approximation option is available in the Layer Model section.
Thin Layer (Heat Transfer Interface)
Two options are available for the Shell type:
•
When the Shell type is Layered shell, the Extra Dimension tool is used to solve the equations through the thickness of a layered material. It is possible to consider several layers with different thermal properties varying through the thickness. This makes the General, Thermally thin approximation, and Thermally thick approximation options available for Layer type in the Layer Model section. You can limit the contribution to individually selected layers by clearing the Use all layers check box. For a given Layered Material Link or Layered Material Stack, you get access to a list of check boxes for the selection of the individual layers.
•
Alternatively, set Shell type to Nonlayered shell, and set a user defined value or expression for the Thickness Lth. This option should be used for thermally thin layers, for which no through-thickness temperature variation is expected in the layered material. This removes the General option from the Layer type list in the Layer Model section.
You can visualize the selected layered materials and layers in each layered material by clicking the Layer Cross Section Preview and Layer 3D Preview buttons.
•
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.
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.
Volume Reference Temperature
This section is available when a temperature-dependent density defined in a material is used. On the material frame, the density is evaluated in relation to a reference temperature in order to ensure conservation of the mass in the presence of temperature variations. By default the Common model input is used. This corresponds to the variable minput.Tempref, which is set to 293.15 K by default. To edit it, click the Go to Source button (), and in the Default Model Inputs node under Global Definitions, set a value for the Volume reference temperature in the Expression for remaining selection section.
The other options are User defined and all temperature variables from the physics interfaces included in the model.
This model input does not override the Reference temperature Tref set in the Physical Model section of the physics interface, which is used to evaluate the reference enthalpy, and a reference density for incompressible nonisothermal flows.
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.
Layer Model
The available options for Layer type are Thermally thin approximation, Thermally thick approximation (available only in the Thin Layer feature), and General.
If Layer type is Thermally thick approximation, from the Specify list select Layer properties (default) or Thermal resistance.
If the Layer type is Thermally thin approximation, and the Shell type is Layered shell, the Layerwise constant properties check box is available to solve the equations with weighted averaged material properties, assuming that these properties are constant within each layer. When suitable, this allows to compute efficiently the homogenized properties of the layered material. By default this check box is not selected, and the properties are integrated through the thickness of the layered material. It means that 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.
Within a layered material selection, a single Layer type should be used. If two layer types are needed for the same layered material, the original material should be duplicated so that one layered material is defined for each layer type. A Shell Continuity (Heat Transfer Interface) and Continuity (Heat Transfer in Shells Interface) node may be added between the two layered materials.
Heat Conduction
The default Thermal conductivity k is taken From layered material. For User defined select Isotropic, Diagonal, Symmetric, or Full to enter another value or expression.
Alternatively, set a value for the Thermal resistance Rs if Specify is set to Thermal resistance in the Layer Model section (for Thermally thick approximation).
Thermodynamics
By default the Density ρ and Heat capacity at constant pressure Cp of the layer are taken From layered material. See Material Density in Features Defined in the Material Frame if a temperature-dependent density should be set. For User defined enter other values or expressions.
When Layer type is Thermally thick approximation, these properties are only used in time-dependent studies, but must be set in all cases.
These subnodes are available for Thin Layer node:
•
Heat Source (Thin Layer, Thin Film, Fracture) — to add a layer internal heat source, Qs, within the layer.
•
 Heat Flux (Thin Layer, Thin Film, Fracture) — to add a heat flux through a specified set of boundaries.
•
Temperature (Thin Layer, Thin Film, Fracture, and Heat Transfer in Shells Interface)  — to set a prescribed temperature condition on a specified set of boundaries.
•
 Surface-to-Ambient Radiation (Thin Layer, Thin Film, Fracture, and Heat Transfer in Shells Interface) — to add a surface-to-ambient radiation for the layer end.
When multiple layers are defined they are numbered from the downside (Layer 1) to the upside. 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.
•
Theory for Heat Transfer in Thin Structures
•
Boundary Wall Temperature
•
Plotting and Evaluating Results in Layered Materials
•
Heat Transfer in a Surface-Mount Package for a Silicon Chip: Application Library path Heat_Transfer_Module/Power_Electronics_and_Electronic_Cooling/surface_mount_package
•
Silica Glass Block Coated with a Copper Layer: Application Library path Heat_Transfer_Module/Tutorials,_Thin_Structure/copper_layer
Location in User Interface
Context Menus
Heat Transfer in Solids>Thin Structures>Thin Layer
Heat Transfer in Shells>Solid
 Ribbon
Physics tab with interface as Heat Transfer in Solids selected:
Boundaries>Thin Layer
Physics tab with interface as Heat Transfer in Shells selected:
Boundaries>Solid