Fracture (Heat Transfer Interface) and Porous Medium (Heat Transfer in Shells Interface)
Use this node to allow heat transfer in fractures on layered materials inside domains. It can also be used to allow heat transfer in films.
Boundary Selection
When the Porous Medium node is added manually in the Heat Transfer in Fractures interface, and for the Fracture 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 Porous Medium is the default node of the Heat Transfer in Fractures interface, it is applied on all boundaries where the Heat Transfer in Fractures 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
Porous Medium (Heat Transfer in Fractures Interface)
Different settings are available, depending on the settings in the Shell Properties section of the parent interface, and whether Porous Medium is the default node or was added manually:
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When the Shell type is Layered shell in the Shells Properties section of the parent interface, the same layered material is used in the Porous Medium node, but 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. In this case, both the General and Thermally thin approximation options are available in the Layer Model section.
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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 Porous Medium node. This option is not editable when Porous Medium is the default node, but you can change to User defined and override the interface 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.
Fracture (Heat Transfer Interface)
Two options are available for the Shell type:
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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 and Thermally thin 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.
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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.
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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.
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.
Absolute Pressure
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 Absolute pressure pA is User defined. 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 Laminar Flow interface is added you can select Absolute pressure (spf) from the list. The Common model input option corresponds to the minput.pA variable, set to 1 atm 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 Pressure in the Expression for remaining selection section.
Layer Model
The available options for Layer type are Thermally thin approximation and General. The former is a lumped model that accounts only for tangential temperature gradients (along the fracture), whereas the latter accounts also for the normal gradients of temperature (through the fracture’s thickness).
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.
Fluid Material
By default, the Boundary material is used.
Heat Conduction, Fluid
The settings are the same as for Thin Film (Heat Transfer Interface) and Fluid (Heat Transfer in Shells Interface).
Heat Conduction, Fluid
The settings are the same as for Thin Film (Heat Transfer Interface) and Fluid (Heat Transfer in Shells Interface).
Thermodynamics, Fluid
The settings are the same as for Thin Film (Heat Transfer Interface) and Fluid (Heat Transfer in Shells Interface).
Porous Material
By default, the Boundary material is used. The Volume fraction θp should be specified. The default is 0.
Heat Conduction, porous matrix
The default Thermal conductivity kp is taken From layered material. For User defined select Isotropic, Diagonal, Symmetric, or Full based on the characteristics of the thermal conductivity, and enter another value or expression. Select an Effective conductivity: Volume average (default) or Power law.
Thermodynamics, porous matrix
The default Density ρp and Specific heat capacity Cp, p 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.
In the Porous Medium node, only in-plane anisotropy is supported for the thermal conductivity of the fracture material.
Fracture in Theory for Heat Transfer in Thin Structures
Location in User Interface
Context Menus
Heat Transfer in Porous Media>Thin Structures>Fracture
Heat Transfer in Fractures>Porous Medium
Ribbon
Physics Tab with interface as Heat Transfer in Porous Media selected:
Boundaries>Fracture
Physics Tab with interface as Heat Transfer in Shells, Heat Transfer in Films or Heat Transfer in Fractures selected:
Boundaries>Porous Medium