Chemical Reaction Engineering Module Updates

For users of the Chemical Reaction Engineering Module, COMSOL Multiphysics® version 6.0 brings an interface for modeling nonisothermal reacting flow, improved handling of porous materials, and a new porous catalyst feature. Read about these updates and more below.

Nonisothermal Reacting Flow

There are now Nonisothermal Reacting Flow multiphysics interfaces that automatically set up nonisothermal reacting flow models. The Reacting Flow multiphysics coupling makes modeling nonisothermal reacting flow much easier. The new formulation gives a consistent energy balance when using reactions from the Chemistry interface and Heat Transfer interface. Previously, the energy balance had to be defined manually. Using the Chemistry interface also gives the ability to use thermodynamic properties from the built-in database in the Chemical Reaction Engineering Module. You can view this new feature in the existing Dissociation in a Tubular Reactor tutorial 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. View this new update in the NOx Reduction in a Monolithic Reactor tutorial model.

Porous Catalyst Feature for Heterogeneous Reactions and Adsorption

The Packed Bed feature is now complemented with a new Porous Catalyst feature available in the Transport of Diluted Species and Transport of Concentrated Species interfaces. This new feature defines a network or packed bed that consists of macropores only. This means that the matrix, skeleton, or particles that form the macroporous matrix are not themselves porous. This simplifies the model definition greatly and covers systems such as porous membranes, filters, and other common devices in chemical engineering and material science. With the new functionality, it is possible to define heterogeneous reactions as well as adsorption and desorption processes.

A steam reformer model showing the temperature in the Heat Camera color table.
Temperature of a steam reformer model.

Turbulent Reacting Flow with Diluted Species

The Reacting Flow, Diluted Species coupling feature has been extended with the capability of treating dilute solutions and turbulent flow. With the new functionality, only solvent–solute interactions are defined, greatly simplifying the definition and solution of the model equations, thus reducing the computational cost. You can see this new feature in the Turbulent Mixing in a Stirred Tank tutorial model.

A plate reactor model showing the concentration in the Rainbow color table.
Concentration of a plate reactor model.

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.

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:

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.

New Method for Computing Viscosity: The Davidson Viscosity Model

A new Davidson model for computing viscosity in multicomponent mixtures based on the different components' contributions to the momentum of a gas in the system. The only data required for computing viscosity in the Davidson model are the molecular weights and the viscosities of the pure components at the given temperature and pressure. The Davidson model is computationally efficient and is as accurate as the best available models for estimating the viscosity of binary gas mixtures.

A monolithic reactor model showing the temperature conversion in the Rainbow color table.
Isosurfaces showing the conversion of NO in a monolithic reactor.

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.

New and Updated Tutorial Models

COMSOL Multiphysics® version 6.0 brings new and updated tutorial models to the Chemical Reaction Engineering Module.