Porous Media Flow Module Updates

For users of the Porous Media Flow Module, COMSOL Multiphysics® version 6.0 brings a new multiphysics interface for modeling finite structural deformations in porous bodies, a new packed beds interface for modeling multiscale heat transfer in pellet beds, and improved handling of porous materials. Learn more about these updates below.

Large-Strain Poroelasticity

The new Poroelasticity, Large Deformation, Solid multiphysics interface allows for modeling finite structural deformations in porous bodies. This is the same as the Poroelasticity, Solid multiphysics interface, available since previous versions, but with an additional Elastic Predeformation node that allows you to track large deformations and rotations. You can find this interface under the Poroelasticity branch in the Structural Mechanics folder in the Add Physics tree. This new interface requires the Structural Mechanics Module.

Two-Phase Flow in Porous Media

A new multiphysics interface combines the Brinkman Equations and the Level Set interfaces, and automatically adds a Two-Phase Flow, Level Set coupling node. It solves the conservation of momentum and a continuity of mass with the Brinkman equations. The interface between two immiscible fluids in porous media is tracked with the level-set function.

Resin showed in the Aurora Australis color table, injecting into an empty mold model. Resin injection into an empty mold. The new interface is used to track the injection front. The mold contains one inlet and three outlets, and a porous block in the center, and it is initially filled with air.

Nonisothermal Flow in Porous Media

The new Nonisothermal Flow, Brinkman Equations multiphysics interface automatically adds the coupling between heat transfer and fluid flow in porous media. It combines the Heat Transfer in Porous Media and Brinkman Equations interfaces. You can see this new feature in the existing Free Convection in a Porous Medium tutorial model.

A porous structure showing the temperature in the Heat Camera color table. The tutorial example Free Convection in a Porous Medium makes use of the new nonisothermal flow functionality. Temperature (K) in a porous structure subjected to temperature gradients and subsequent free convection.

Porous Slip for the Brinkman Equations Interface

The boundary layer in flow in porous media may be very thin and impractical to resolve in a Brinkman equations model. The new Porous slip wall treatment feature allows you to account for walls without resolving the full flow profile in the boundary layer. Instead, a stress condition is applied at the surfaces, yielding decent accuracy in bulk flow by utilizing an asymptotic solution of the boundary layer velocity profile. The functionality is activated in the Brinkman Equations interface Settings window and is then used for the default wall condition. You can use this new feature in most problems involving subsurface flow described by the Brinkman equations and where the model domain is large.

A porous reactor model showing the flow and concentration in the Rainbow color table. The flow and concentration field of a porous reactor model.

Greatly Improved Handling of Porous Materials

Porous materials are now defined in the Phase-Specific Properties table in the Porous Material node. In addition, subnodes may be added for the solid and fluid features where several subnodes may be defined for each phase. This allows for the use of one and the same porous material for fluid flow, chemical species transport, and heat transfer without having to duplicate material properties and settings.

A closeup view of the Model Builder with the Porous Material node highlighted, the corresponding Settings window, and a packed-bed reactor model in the Graphics window The new Materials node for Porous Material exemplified on a multiscale model of a packed bed.

Multiscale Heat Transfer in Pellet Beds

A new Heat Transfer in Packed Beds interface has been added to model heat transfer in pellet beds. The pellet bed is represented as a porous medium made up of fluid and pellets. The pellets are modeled as spherical homogenized porous particles in which the temperature varies radially. The temperature distribution in the pellets is computed for every position in the packed bed. It is coupled to the temperature in the surrounding fluid through an interstitial heat flux between the pellets' surfaces and the fluid.

The new functionality is useful for modeling heat in packed bed thermal energy storage systems or the chemical reaction in a packed bed when coupled with the corresponding feature for transport of chemical species. View this new feature in the new Packed Bed Thermal Energy Storage System tutorial model.

A single pellet bed model showing the temperature distribution within in the Heat Camera color table. Temperature distribution inside a solid pellet located at the middle of the geometry.
Eleven pellet beds on a domain showing the temperature distribution in the Heat Camera color table. Fluid and pellet temperature in the entire domain.

Velocity at Walls for Moisture Evaporation and Condensation

Surface reactions, such as evaporation or condensation, result in a net vapor flux between the surface and surrounding domain. This type of reaction corresponds to an effective moist air velocity at the domain boundary, called the Stefan velocity. Whenever large evaporation rates are expected, the Stefan flow should be taken into account as it can be important in the overall behavior of the system. In the Moisture Flow multiphysics coupling, an Account for Stefan velocity at walls check box is now available when the Concentrated Species formulation is used in the Moisture Transport interface. This is recommended in evaporation and condensation applications when the temperature is high, typically above 50°C. You can see this feature in the new Modeling of Stefan Flow Due to Evaporation from a Water Surface tutorial model.

A model with isosurface plots showing the relative humidity in blue and red streamlines showing the velocity. Relative humidity isosurfaces and velocity streamlines due to Stefan flow over the evaporation surface, when the ambient temperature is 90°C.

Moisture Transport Improvements

The Moisture Transport interfaces now provide a Periodic Condition feature that enables you to reduce the simulation domain for a periodic structure or to evaluate effective properties from a representative cell. In addition, the Hygroscopic Porous Media feature has been updated to match the classical design for features for porous materials. The variables for energy balance have been optimized for a much faster evaluation and new variables are now available to check the mass balance. You can see the moisture transport improvements in the new Drying of a Potato Sample tutorial model and these existing models:

A 2D potato sample model showing the relative humidity in the Jupiter Aurora Borealis color table. Relative humidity in a potato sample exposed to dry air flow.

Heat Transfer in Porous Media

The heat transfer in porous media functionality has been revamped to make it more user friendly. A new Porous Media physics area is now available under the Heat Transfer branch and includes the Heat Transfer in Porous Media, Local Thermal Nonequilibrium, and Heat Transfer in Packed Bed interfaces. All of these interfaces are similar in function, the difference being that the default Porous Medium node within all these interfaces has one of three options selected: Local thermal equilibrium, Local thermal nonequilibrium, or Packed bed. The latter option has been described above and the Local Thermal Nonequilibrium interface has replaced the multiphysics coupling and corresponds to a two-temperature model, one for the fluid phase and one for the solid phase. Typical applications can involve rapid heating or cooling of a porous medium due to strong convection in the liquid phase and high conduction in the solid phase like in metal foams. When the Local Thermal Equilibrium interface is selected, new averaging options are available to define the effective thermal conductivity depending on the porous medium configuration.

In addition, postprocessing variables are available in a unified way for homogenized quantities for the three types of porous media. View the new porous media additions in these existing tutorial models: