Porous Matrix
This node defines the porosity and material properties of the solid matrix of the Porous Medium or Unsaturated Porous Medium parent node.
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.
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 porosities of the Solid and Immobile Fluids subnodes under the Porous Material node. See Porous Material in the COMSOL Multiphysics Reference Manual for more information.
Select User defined to enter a value or expression for εp.
If required by a Storage model in the parent node, specify the Effective compressibility of the porous matrix. The default value is χp = 10−4 1/Pa.
Select a Permeability model to specify the capacity of the porous material to transmit flow. Which options are available depends on the Flow model setting in the parent node. Note that for the Unsaturated Porous Medium parent node only the Darcian Flow models are available.
Darcian Flow
If Darcian flow is selected in the parent Porous medium node, select between the following options for the Permeability model:
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Select Permeability (default) to define the permeability of the porous matrix. The default Permeability κ (SI unit: m2) uses the value From material, as defined by the Porous material. For User defined select Isotropic to define a scalar value or Diagonal or Symmetric to define a tensor value.
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Select Hydraulic conductivity or define a combination of fluid permeability and dynamic viscosity. For Hydraulic conductivity K (SI unit: m/s) select Isotropic to define a scalar value or Diagonal or Symmetric to define a tensor value. The default is 2.94·10−4 m/s.
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Select Kozeny–Carman to define the permeability from the porosity and mean particle diameter. Enter the mean Particle diameter dp (SI unit: m), the default value is 0.5 mm.
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Select Power law to define the permeability as an exponential function of the porosity: κ=bPlεpn, where bPl and n are empirical parameters. Enter the proportionality factor bPl (SI unit: m2) and the exponent n (dimensionless).
Non-Darcian Flow
If Non-Darcian flow is selected in the parent node, select between the following options for the Permeability model:
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For Forchheimer, the default Permeability κ (SI unit: m2) uses the value From material. Furthermore, the dimensionless Forchheimer parameter cF can be defined. The default value is 0.55.
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If Ergun is selected, enter the mean Particle diameter dp (default value: 0.5 mm).
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For Burke–Plummer, specify the mean Particle diameter dp (default value: 0.5 mm).
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For Klinkenberg, the default Permeability κ∞ (SI unit: m2) uses the value From material. Enter the Klinkenberg parameter bK. Its default value is 103 Pa.
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For User defined, the default Permeability κ (SI unit: m2) uses the value From material. In addition, the Inertial resistance coefficient β (SI unit: 1/m) can be defined. Its default value is zero.
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About Darcian and Non-Darcian Flow in the Porous Media Flow Module User’s Guide
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Permeability Models in the Porous Media Flow Module User’s Guide
Note that some options are only available in some modules. For a detailed overview of the functionality available in each product, visit www.comsol.com/products/specifications/
Retention Model
For an Unsaturated Porous Medium select between the following options for the retention model:
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van Genuchten, to specify the retention model using the van Genuchten relationship. Enter the constitutive relation constants α (the default value is 1, and the SI unit is 1/m), n (default value is 2), and l (default value is 0.5). The constitutive parameter m is equal to 1 − 1 / n.
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Brooks and Corey to use the retention model according to the Brooks and Corey relationships.
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User defined to use a different retention model. Enter user defined expressions for the Effective saturation Se, the Liquid volume fraction θl. The default is εp (the porosity variable). Specify the Specific moisture capacity Cm (SI unit: 1/m). The default value is 0 (1/m). Enter an expression for the Relative permeability κr. The default value is 1.
If there is a residual volume of liquid that cannot move through the pore network, also enter a value between 0 and 1 for the Residual liquid volume fraction θr. The default value is 0.
Retention and Permeability Relationships in the Subsurface Flow Module User’s Guide
Location in User Interface
A default Porous Matrix node is automatically added to Porous Medium or the Unsaturated Porous Medium node.
Context Menus
Darcy’s Law > porous medium feature > Fluid
Richards’ Equation > porous medium feature > Fluid