Geothermal Heating
Use this node to account for the contribution of geothermal heat production by adding a source term Qgeo to the right-hand side of the heat equation:
The predefined expression of the heat source uses the Geothermal Density, the Radiogenic heating per unit mass, and a distribution function that can be set.
Geothermal Heat Production
Specify the Radiogenic heating per unit mass qgeo.
The two option buttons in the same group control the distribution function f(zgeo):
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If  Uniform distribution is selected, f(zgeo) = 1 and the geothermal heat source is assumed to be independent on depth.
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If  Exponential distribution is selected, two additional input fields are displayed underneath. The exponential distribution f(zgeo) = exp(zgeo ⁄ hgeo), is defined by the constant Length scale: hgeo and the variable Depth zgeo. The depth can be, for example, the vertical coordinate direction. The heat source achieves its maximum value where zgeo = 0, typically the top surface of a model.
Geothermal Density
Select the Geothermal density: Solids, Porous media, or User defined:
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If  Solids is selected, it calculates the geothermal density based on the volume fraction of solid material
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 If Porous media is selected, it calculates the geothermal density based on all mobile and immobile components of the porous medium:
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 If User defined is selected, enter a value for the Geothermal density ρgeo.
The Geothermal Heating subnode requires the Subsurface Flow Module. For a detailed overview of the functionality available in each product, visit http://www.comsol.com/products/specifications/
Location in User Interface
Context menus
If the Porous matrix model is set to Extended under the Physical Model section:
Heat Transfer in Porous Media>Porous Medium>Geothermal Heating
More locations are available if the Heat transfer in porous media check box is selected and Porous matrix model is set to Extended under the Physical Model section. For example:
Heat Transfer in Solids>Porous Medium>Geothermal Heating
Ribbon
Physics Tab with Porous Medium selected in the model tree:
Attributes>Porous Medium>Geothermal Heating