The Fluid and Matrix Properties node adds the equations for Darcy’s law, Equation 4-6 and Equation 4-7 (excluding any mass sources), and contains settings for the fluid properties and the porous matrix properties such as the effective porosity.

Select the Fluid material to use for the fluid properties. Select Domain material (the default) to use the material defined for the domain. Select another material to use that material’s properties for the fluid.

The default Density ρ (SI unit: kg/m3) uses values From material based on the Fluid material selection.

Select a Dynamic viscosity μ (SI unit: Pa·s). The default uses values From material as defined by the Fluid material selected. For User defined the default is 0 Pa·s.

If the settings for the dynamic viscosity are unavailable, this is due to Hydraulic conductivity being selected as the Permeability model under the Matrix Properties section below. The hydraulic conductivity is defined using a combination of fluid and matrix properties and replaces the need to define the dynamic viscosity. Note that this option is only available with the Subsurface Flow Module.

Select the material to use as porous matrix. Select Domain material from the Porous material list (the default) to use the material defined for the porous domain. Select another material to use that material’s properties.

The default Porosity εp (a dimensionless number between 0 and 1) uses the value From material, defined by the Porous material selected. For User defined the default is 0.

Select a Permeability model to specify the capacity of the porous material to transmit flow — Permeability to define the permeability of the porous matrix, Hydraulic conductivity to define a combination of fluid permeability and dynamic viscosity, Kozeny-Carman to define the permeability from the porosity and mean particle diameter, or Non-Darcian in cases when Darcy’s linear relation between pressure drop and velocity is no longer valid due to turbulence or inertial effects.

Note that the option to choose Hydraulic conductivity is only available for the Subsurface Flow Module. The Non-Darcian Flow option is only available in some modules. For a detailed overview of the functionality available in each product, visit https://www.comsol.com/products/specifications/.

The default Permeability κ (SI unit: m2) uses the value From material, as defined by the Porous material list. For User defined select Isotropic to define a scalar value or Diagonal, Symmetric, or Full to define a tensor value and enter another value or expression in the field or matrix.

For Hydraulic conductivity K (SI unit: m/s) select Isotropic to define a scalar value or Diagonal, Symmetric, or Full to define a tensor value. The default is 2.94·10−4 m/s.

For Kozeny–Carman, enter the mean Particle diameter dp (SI unit: m), the default value is 0.5 mm.

For Non-Darcian, choose a Non-Darcian flow model from the selection list. The available options, depending on the modules licensed, are Forchheimer, Ergun, Burke–Plummer, and Klinkenberg.

For Forchheimer, the default Permeability κ (SI unit: m2) uses the value From material, as defined by the Porous material list. Furthermore, the dimensionless Forchheimer parameter cF can be defined. The default value is 0.55.

If Ergun is selected, enter the mean Particle diameter dp (default value: 0.5 mm). The permeability κ is then calculated using Equation 2-4de.

For Burke–Plummer, specify the mean Particle diameter dp (default value: 0.5 mm).

If Klinkenberg is selected from the list, the default Permeability κ∞ (SI unit: m2) uses the value From material, as defined by the Porous material list. Enter the Klinkenberg parameter bK. Its default value is 1e3 Pa. The corrected permeability κ is then calculated using Equation 2-7de.