Thin Film (Heat Transfer Interface) and Fluid (Heat Transfer in Shells Interface)

For a manually added node in the Heat Transfer in Films interface, or for a node in the Heat Transfer interface, select the check box to make the node applicable only if a layered material is defined on the boundary. If a layered material ( with specified, , , or ) is available, its name is then displayed beside the boundary index (for example, slmat1), otherwise the boundary is marked as not applicable.

The default node of the Heat Transfer in Films interface is applied on all boundaries where the Heat Transfer in Films interface is applied, and neither the boundary selection nor the check box are editable.

Note that when the is in the section of the parent interface or node, the check box is not editable.

Different settings are available, depending on the settings in the Shell Properties section of the parent interface, and whether is the default node or was added manually:

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When the is in the section of the parent interface, the same layered material is used in the node, but you can limit the contribution to individually selected layers by clearing the check box. For a given or , you get access to a list of check boxes for the selection of the individual layers. In this case, both the and options are available in the section.

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When the is in the section of the parent interface, the is taken in the node. This option is not editable when is the default node, but you can change to and override the interface setting with a specific value or expression for Lth when the node was added manually. In this case, only the option is available in the section.

Two options are available for the :

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When the is , 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 and options available for in the section. You can limit the contribution to individually selected layers by clearing the check box. For a given or , you get access to a list of check boxes for the selection of the individual layers.

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Alternatively, set to , and seta user defined value or expression for the Lth. This option should be used for thermally thin layers, for which no through-thickness temperature variation is expected in the layered material. This makes the only option available for in the section.

You can visualize the selected layered materials and layers in each layered material by clicking the and buttons.

	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.

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.

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 field, click (

). The available options are (default), (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 button (

), and in the node under , set a value for the in the section.

Absolute pressure is used in certain predefined quantities that include enthalpy (the energy flux, for example).

It is also used if the ideal gas law is applied. See Thermodynamics, Fluid.

The default pA is . When additional physics interfaces are added to the model, the absolute pressure variables defined by these physics interfaces can also be selected from the list. For example, if a interface is added you can select from the list. The option corresponds to the minput.pA variable, set to 1 atm by default. To edit it, click the button (

), and in the node under , set a value for the in the section.

The available options for are ,and (when the is in the Shell Properties section). The former is a lumped model that accounts only for tangential temperature gradients (along the film), whereas the latter accounts also for the normal gradients of temperature (through the film’s thickness). The second model may be used for the modeling of bearings for example.

If the is , and the is , the 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. When this check box is not selected, 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.

The settings are the same as in the Fluid domain feature.

The settings are the same as in the Fluid domain feature, except for the available options in the list: , , and .

See the Fluid domain feature for more details on the and options.

If is selected, the thermodynamics properties are defined as a function of the amount of vapor in moist air. The options available to define this amount are as follows:

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to define the ratio between vapor mass and total mass. Enter a value or expression for the ω.

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to define the amount of water vapor in the total volume. If selected, a model input is added to the section.

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(default), also called mixing ratio or humidity ratio, to define the ratio between water vapor mass and dry air mass. For , enter a value or expression for the xvap. Else, select an defined in an node under .

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ϕw, a quantity defined between 0 and 1, where 0 corresponds to dry air and 1 to air saturated with water vapor. The

and

should be specified.