The Fluid and Matrix Properties node adds the Brinkman equations: Equation 7-9 and Equation 7-10 (excluding any mass sources), and provides an interface for defining the properties of the fluid material and the porous matrix.

The default Fluid material uses the Domain material. Select another material as needed.

Both the default Density ρ (SI unit: kg/m3) and Dynamic viscosity μ (SI unit: Pa·s) use values From material based on the Fluid material selection. For User defined enter another value or expression. In this case, the default is 0 kg/m3 for the density and 0 Pa·s for the dynamic viscosity. The dynamic viscosity describes the relationship between the shear stresses and the shear rate in a fluid. Intuitively, water and air have a low viscosity, and substances often described as thick, such as oil, have a higher viscosity. Non-Newtonian fluids have a viscosity that is shear-rate dependent. Examples of non-Newtonian fluids include yogurt, paper pulp, and polymer suspensions.

The default Porous material uses the Domain material for the porous matrix. Select another material as needed.

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

Select a Permeability model to specify the capacity of the porous material to transmit flow — Permeability to directly enter the permeability of the porous matrix, 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and mean particle diameter, or Non-Darcian in cases when Darcy’s linear relation between pressure drop and velocity is no longer valid due to turbulence or inertial effects. The Non-Darcian Flow option includes different models, some of them are only available for certain 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 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 or Ergun.

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 2-4 in the Porous Media Flow Module User’s Guide.