Moist Porous Medium
This node uses the following version of the heat equation to model heat transfer in a porous matrix, possibly consisting of several solids, and filled with moist air and liquid water:
(6-6)
(6-7)
See Theory for Heat Transfer in Moist Porous Media for more details on the variables in Equation 6-6 and Equation 6-7.
The effective volumetric heat capacity at constant pressure is defined as
where sl is the liquid water saturation.
If the porous matrix consists of several solids i of volume fraction θsi, heat capacity Cp,si, and density ρsi, the above equation is modified as follows:
Note that the velocity fields in moist air and liquid water, ug and ul, can be defined either as an analytic expression or as the velocity field from a Fluid Flow interface. They should be interpreted as Darcy velocities, that is, as the volume flow rate per unit cross sectional area.
Q (SI unit: W/m3) can be any source (or sink) of heat. Add one or more heat sources as separate physics features. See Heat Source node for example. When the Heat and Moisture multiphysics coupling is active, this term includes the diffusive flux of thermal enthalpy and the liquid capillary flux, calculated from the moisture transport equation.
Qevap (SI unit: W/m3) is the source (or sink) of heat due to phase change of water. When the Heat and Moisture multiphysics coupling is active, it calculates this term from the moisture transport equation.
Coordinate System Selection
Select a coordinate system from the Coordinate system list for the interpretation of directions in anisotropic material properties. The default is the Global coordinate system, and the list contains any additional coordinate system (except boundary coordinate systems) added under the Definitions node.
The subnodes of Moist Porous Medium inherit these coordinate system settings. In particular, the Velocity field (in Moist Air (Moist Porous Medium) subnode) and the Dry bulk thermal conductivity and Solid phase thermal conductivity (in Porous Matrix (Porous Medium, Moist Porous Medium) subnode) should be set according to the coordinate system selected in this section.
See Coordinate Systems in the COMSOL Multiphysics Reference Manual for more details.
Porous Medium Model Settings
This section defines the averaging model for the computation of the Effective thermal conductivity keff, taking into account the properties of the solid matrix, moist air, and liquid water. The following options are available:
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Plane layers parallel to heat flow (default), which calculates the effective conductivity of the moist porous medium as the weighted arithmetic mean (or volume average) of the conductivities of the porous matrix, moist air, and liquid water:
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Plane layers perpendicular to heat flow, which calculates the effective conductivity of the moist porous medium as the weighted harmonic mean (or reciprocal average) of the conductivities of the porous matrix, moist air, and liquid water:
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Power law, which calculates the effective conductivity of the moist porous medium as the weighted geometric mean of the conductivities of the porous matrix, moist air, and liquid water:
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Solid spherical inclusions, which calculates the effective conductivity of the moist porous medium as:
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Fluid spherical inclusions, which calculates the effective conductivity of the moist porous medium as:
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Wrapped screen, which calculates the effective conductivity of the moist porous medium as:
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Sintered metal fibers, which calculates the effective conductivity of the moist porous medium system as:
If the porous matrix consists of several solids i of volume fraction θsi and thermal conductivity ksi, the above equations are modified by replacing ks by , and θs by .
 
It is also possible to define directly the equivalent thermal conductivity, keq When Equivalent thermal conductivity is selected in the Effective thermal conductivity list, a value for the Equivalent thermal conductivity keq should be specified directly. The default Equivalent thermal conductivity is taken From material. When a Porous Material node is active, the property of the Homogenized Properties section is used. For User defined, select Isotropic, Diagonal, Symmetric, or Full based on the characteristics of the thermal conductivity, and enter another value or expression. For Isotropic, enter a scalar which will be used to define a diagonal tensor. For the other options, enter values or expressions into the editable fields of the tensor.
The velocity field and the moisture content of moist air can be specified in the Moist Air (Moist Porous Medium) subnode.
The liquid water saturation and velocity field can be specified in the Liquid Water (Moist Porous Medium) subnode.
The porosity and material properties of the solid matrix can be specified in the Porous Matrix (Porous Medium, Moist Porous Medium) subnode.
See Porous Material in the COMSOL Multiphysics Reference Manual.
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Theory for Heat Transfer in Moist Porous Media
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Theory for Heat Transfer in Moist Air
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Heat and Moisture
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.
For a detailed overview of the functionality available in each product, visit https://www.comsol.com/products/specifications/
Location in User Interface
Context Menus
Heat Transfer in Moist Porous Media>Specific Media>Moist Porous Medium
Ribbon
Physics tab with Heat Transfer in Moist Porous Media selected:
Domains>Specific Media>Moist Porous Medium