Porous Matrix (Porous Medium, Moist Porous Medium)
This node defines the porosity and material properties of the solid matrix used in the heat transfer equations of the Moist Porous Medium and Porous Medium parent nodes, to model heat transfer in a porous matrix, possibly consisting of several solids, and filled with a mobile fluid, and one or more immobile fluids.
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The velocity field and material properties of the mobile fluid can be specified in the Fluid (Porous Medium) subnode, by defining it as a general gas or liquid, as an ideal gas, or as moist air.
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The total volume fraction and material properties of immobile fluids can be specified in the Immobile Fluids (Porous Medium) subnode.
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.
Other options are User defined and all the 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.
Matrix Properties
The default Porosity εp of the solid matrix is taken From material. In a Porous Material node, the porosity is defined as follows:
where θsi and θimfi are the volume fractions of the Solid and Immobile Fluids subnodes under the Porous Material node.
For User defined, enter a value or expression.
Choose to define either the Dry bulk properties or the Solid phase properties for thermal conductivity, density, and heat capacity at constant pressure of the porous matrix. The first option sets the properties of the matrix including empty pores, while the second option defines the properties of the pure solid phase.
Heat Conduction, Porous Matrix
The thermal conductivity ks describes the relationship between the heat flux vector q and the temperature gradient ∇T in q = −ks∇T, which is Fourier’s law of heat conduction. Enter this quantity as power per length and temperature.
The default Thermal conductivity ks is taken From material. 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.
When the thermal conductivity is taken From material and more than one Solid subnode is added under the Porous Material node, the average property is obtained by applying a volume average model:
Alternatively, set the Dry bulk thermal conductivity kb, when Define is set to Dry bulk properties in the Matrix Properties section. The corresponding property for the solid phase is then defined as:
Note that this section is not available when Porous medium type is set to Local thermal equilibrium and Equivalent thermal conductivity is selected in the Effective thermal conductivity list of the Porous medium parent node.
Thermodynamics, Porous Matrix
This section defines the thermodynamics properties of the porous matrix.
The specific heat capacity describes the amount of heat energy required to produce a unit temperature change in a unit of mass of the solid material.
The Density ρs and the Specific heat capacity Cp, s should be specified. For From Material option, see Material Density in Features Defined in the Material Frame if a temperature-dependent density should be set.
When the density and specific heat capacity are taken From material and more than one Solid subnode is added under the Porous Material node, the effective properties are obtained by applying a volume averaging model:
Alternatively, set the Dry bulk density ρb and the Dry bulk heat capacity at constant pressure Cp,b when Define is set to Dry bulk properties in the Matrix Properties section. The corresponding properties for the solid phase are then defined as:
and
When the porosity εp is taken From material, the solid volume fraction θs is defined in the material, under the Solid subnode. In case of multiple solids, it is needed to refer to the material, as it is not possible to deduce the values of θsi for the different solids from the porosity. When the porosity is User defined, the volume fraction of each solid θsi is obtained by dividing θs =1-εp by the number of solids.
When the Porous Medium type is set to Local thermal nonequilibrium in the Porous Medium parent node, the Initial Values, Heat Source, Thermal Insulation, Symmetry (Heat Transfer Interface), Temperature, Heat Flux, Lumped System Connector, Continuity, Boundary Heat Source, Surface-to-Ambient Radiation (Heat Transfer Interface), and Deposited Beam Power features are available under the Porous Matrix subnode.These subnodes allow the definition of domain and boundary conditions specific to the fluid phase temperature Ts.
Location in User Interface
Context Menus
Heat Transfer in Porous Media>Porous Medium>Porous Matrix
Heat Transfer in Moist Porous Media>Moist Porous Medium>Porous Matrix
Ribbon
Physics tab with Porous Medium or Moist Porous Medium selected in the model tree:
Attributes>Porous Matrix