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ρ (SI unit: kg/m3) is the density of the mobile fluid.
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Cp (SI unit: J/(kg·K)) is the heat capacity at constant pressure of the mobile fluid.
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(ρCp)eff (SI unit: J/(m3·K)) is the effective volumetric heat capacity at constant pressure, defined by an averaging model to take into account both solid matrix and fluid properties.
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q is the conductive heat flux (SI unit: W/m2).
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u (SI unit: m/s) is the velocity field of the mobile fluid, either an analytic expression or the velocity field from a Fluid Flow interface. u should be interpreted as the Darcy velocity, that is, the volume flow rate per unit cross sectional area. The average linear velocity (the velocity within the pores) can be calculated as uL = u ⁄ εp, where εp is the porosity.
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keff (SI unit: W/(m·K)) is the effective thermal conductivity (a scalar or a tensor if the thermal conductivity is anisotropic), defined by an averaging model to take into account both solid matrix and fluid properties.
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Q (SI unit: W/m3) is the heat source (or sink). Add one or more heat sources as separate physics features. See Heat Source node and Viscous Dissipation subnode for example.
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Volume average (default), which calculates the effective conductivity of the solid-fluid system as the weighted arithmetic mean of the conductivities of the fluid and the porous matrix:
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Reciprocal average, which calculates the effective conductivity of the solid-fluid system as the weighted harmonic mean of the conductivities of the fluid and the porous matrix:
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Power law, which calculates the effective conductivity of the solid-fluid system as the weighted geometric mean of the conductivities of the fluid and the porous matrix:
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With some COMSOL products, the Thermal Dispersion, Viscous Dissipation, and Geothermal Heating subnodes are available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
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