Surface-to-Ambient Radiation, Interface (Heat Transfer in Shells Interface)
Use this node to add surface-to-ambient radiation on the exterior interfaces of a shell and, for the case of a layered shell, at the interfaces between its layers. The net inward heat flux due to surface-to-ambient radiation is
where ε is the surface emissivity, σ is the Stefan-Boltzmann constant (a predefined physical constant), and Tamb is the ambient temperature.
Boundary Selection
Select the boundaries on which to add surface-to-ambient radiation.
In addition, 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.
Note that when the Shell type is Nonlayered shell in the Shells Properties section of the parent interface, the Restrict to layered boundaries check box is not editable.
Interface Selection
Set the interfaces for which surface-to-surface radiation should be considered. These can be internal interfaces between layers or the top and bottom surfaces.
Different settings are available, depending on the settings in the Shell Properties section of the parent interface:
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When the Shell type is Layered shell in the Shells Properties section of the parent interface, the available options in the Apply to list are Top interface, Bottom interface, Exterior interfaces, Interior interfaces, All interfaces, and Selected interfaces. With the last option you can select any set of interfaces for a given layered material, by clearing the check boxes corresponding to layer interfaces where the node should not be applied in the Selection table. The top and bottom interfaces refer respectively to the upside and downside of the boundary, defined from the orientation of the normal vector. See Interface Selections for more details on the interfaces identification.
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When the Shell type is Nonlayered shell in the Shells Properties section of the parent interface, a single layer material is defined on the boundary, and the available options in the Apply to list are Top interface, Bottom interface, and All interfaces. This setting has no effect unless the temperature differs from one side of the boundary to the other.
You can visualize the selected interfaces by clicking the Layer Cross Section Preview and Layer 3D Preview buttons.
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For a general description of layer and interface selections, see Layer and Interface Selection Tools.
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You can provide material parameters with a through-thickness variation by explicitly or implicitly 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.
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.
Surface-to-Ambient Radiation
Surface Emissivity
The default Surface emissivity ε (a dimensionless number between 0 and 1) is taken From layered material. For User defined, it should be specified. An emissivity of 0 means that the surface emits no radiation at all while an emissivity of 1 means that it is a perfect blackbody.
Ambient Temperature
For User defined, enter an Ambient temperature Tamb. Else, select an Ambient temperature defined in an Ambient Properties node under Definitions.
In 2D, the equation has an additional factor, dz, to take into account the out-of-plane thickness.
Theory for Heat Transfer in Thin Structures
Location in User Interface
Context Menus
Heat Transfer in Shells>Interfaces>Surface-to-Ambient Radiation, Interface
Heat Transfer in Films>Interfaces>Surface-to-Ambient Radiation, Interface
Heat Transfer in Fractures>Interfaces>Surface-to-Ambient Radiation, Interface
Ribbon
Physics tab with Heat Transfer in Shells selected in the model tree:
Boundaries>Surface-to-Ambient Radiation, Interface