Fluent Porous Media English Help File Full719 Porous Media ConditionsThe porous media model can be used for a wide variety of problems including flows through packed beds filter papers perforated plat

ically present in the porous media is not explicitly considered, it is assumed that the porous medium is homogeneous, isotropic, and continuous in the flow direction. This means that the medium has uniform properties throughout and is unbiased in any particular direction.

l The porous media model assumes an incompressible flow regime. This means that the density of the fluid is assumed to be constant throughout the model. If the flow regime is compressible, then you should not use the porous media model.

l The porous media model assumes that the fluid flow through the medium is laminar. This means that the Reynolds number of the flow is low enough such that turbulence is not present.

l The porous media model assumes that the flow through the medium is in the fully-developed regime. This means that the flow has reached a steady-state and is not subject to any acceleration or deceleration.

l The porous media model assumes that the fluid and the medium are in thermal equilibrium. This means that the temperature of the fluid and the medium are equal at any given point in the model.

7.19.2 Momentum Equations for Porous Media

The momentum equations for the porous media model are based on Darcy's law, which relates the pressure drop across the porous medium to the fluid velocity. The momentum equations are given by:

∇P = -fμu

where P is the pressure, f is the friction factor, μ is the dynamic viscosity of the fluid, and u is the velocity of the fluid. The friction factor f is a function of the Reynolds number of the flow and the porosity of the medium.

7.19.3 Treatment of the Energy Equation in Porous Media

The energy equation for the porous media model is based on the assumption of thermal equilibrium between the fluid and the medium. This means that the temperature of the fluid and the medium are equal at any given point in the model. The energy equation is given by:

ρCp(∂T/∂t) + ρCp(u·∇T) = k∇^2T

where T is the temperature, ρ is the density of the fluid, Cp is the specific heat capacity of the fluid, k is the thermal conductivity of the medium.

7.19.4 Treatment of Turbulence in Porous Media

The porous media model assumes that the flow through the medium is laminar. Therefore, turbulence modeling is not required for the porous media model.

7.19.5 Effect of Porosity on Transient Scalar Equations

The porosity of the medium affects the transient scalar equations in the porous media model. The porosity is defined as the ratio of the volume of the void space in the medium to the total volume of the medium. The transient scalar equations are given by:

ρ(∂φ/∂t) + ρ(u·∇φ) = D∇^2φ

where φ is the scalar quantity being transported, ρ is the density of the fluid, u is the velocity of the fluid, D is the diffusion coefficient of the scalar quantity.

7.19.6 User Inputs for Porous Media

The user inputs for the porous media model include the porosity of the medium, the permeability of the medium, and the pressure drop across the medium. The porosity and permeability of the medium are used to calculate the friction factor f in the momentum equations. The pressure drop across the medium is used to calculate the velocity of the fluid.

7.19.7 Modeling Porous Media Based on Physical Velocity

The porous jump model can be used to model a thin membrane with known velocity/pressure-drop characteristics. The porous jump model is applied to a face zone, not to a cell zone, and should be used (instead of the full porous media model) whenever possible because it is more robust and yields better convergence.

7.19.8 Solution Strategies for Porous Media

The solution strategies for the porous media model include using a segregated solver, using a coupled solver, or using a user-defined function (UDF) to specify the pressure drop across the medium.

7.19.9 Postprocessing for Porous Media

The postprocessing for the porous media model includes visualizing the flow velocity, pressure, and temperature distributions in the porous medium. The postprocessing can also include calculating the overall pressure drop across the medium and the heat transfer rate between the fluid and the medium