Line Heat Source
This node models a heat source (or sink) that is so thin that it has no thickness in the model geometry. It is available in 3D on edges. In 2D and 2D axisymmetric, it is available on points.
In theory, the temperature in a line source in 3D is plus or minus infinity (to compensate for the fact that the heat source does not have any volume). The finite element discretization used in COMSOL Multiphysics returns a finite temperature distribution along the line, but that distribution must be interpreted in a weak sense.
Material Type
Select an option in the Material type list to specify if the inputs of the Line Heat Source section are defined in the material or spatial frame:
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The default option for the Line Heat Source node is Solid, which specifies that the heat source Ql is defined in the material frame. Because the heat transfer variables and equations are defined in the spatial frame, the inputs are internally converted to the spatial frame. See Conversion Between Material and Spatial Frames for details.
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The Nonsolid option defines Ql in the spatial frame. No frame conversion is needed.
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The From material option uses the option selected in the Material type list of the Material Properties section of the material applied on the domain on which the node is active.
This option has no effect when the component does not contain a moving frame because the material and spatial frames are identical in such cases. With a Deformed Geometry or a Moving Mesh interface, the heat transfer features automatically account for deformation effects of the material and spatial frames on heat transfer properties. In particular the effects of volume changes on the density are considered. See Handling Frames in Heat Transfer and Material and Spatial Frames for details.
Line Heat Source
Click the General source (the default) or Heat rate button.
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If General source is selected, enter a value for the distributed heat source, Ql in unit power per unit length. A positive Ql corresponds to heating while a negative Ql corresponds to cooling.
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If Heat rate is selected, enter the heat rate Pl.
Heat Source Radius
With the Heat Transfer Module, you can model the heat source explicitly and apply it on a cylinder around the line. This section is not available when the node is added under the Thin Rod feature.
Select the Specify heat source radius check box to define the Heat source radius R. This averages the source on a cylinder of given radius around the line. This option avoids obtaining an increasing temperature value at the line when meshing finer than this radius. It makes use of the diskavg operator for averaging around the source.
See Built-In Operators in the COMSOL Multiphysics Reference Manual for additional information about the diskavg operator.
You can specify the source to be a harmonic perturbation in a frequency domain analysis. To mark the source as being a harmonic perturbation, right-click the node and choose Harmonic Perturbation. Note that this updates the node’s icon. See Theory for Harmonic Heat Transfer for more details.
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Handling Frames in Heat Transfer
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About the Heat Transfer Interfaces
Location in User Interface
Context menus
 Heat Transfer>support>Line Heat Source
Heat Transfer in Solids>support>Line Heat Source
Heat Transfer in Fluids>support>Line Heat Source
Heat Transfer in Porous Media>support>Line Heat Source
Bioheat Transfer>support>Line Heat Source
Heat Transfer in Solids>support>Thin Rod>Line Heat Source
Ribbon
Physics Tab with Heat Transfer, Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media, Heat Transfer in Building Materials, or Bioheat Transfer selected:
support>Line Heat Source
support>Thin Rod>Line Heat Source
with support as Egdes in 3D and Points in 2D.