New Functionality in Version 4
- You can now add and remove species in the Chemical Species Transport physics interfaces. This means that you do not have to start with all species in your transport model. Instead you can add species one by one, thus reducing the risks for introducing errors.
- Two new diffusion models, a mixture-averaged diffusion model and a model based on Fick’s law, are introduced in the Transport of Concentrated Species interface. These diffusion models are less computationally demanding than the Maxwell-Stefan diffusion model, and the latter model require less input data for the interaction between species in the mixture. The new models can be used in convection dominated problems, where high accuracy in the diffusion interaction is not required, or when interaction data is not available.
- The improved stabilization for Chemical Species Transport in version 4 yields higher accuracy with a relatively coarse mesh compared to version 3.5a. This also results in increased robustness and less computational cost for a given accuracy compared to previous versions.
- The possibility to include a Forchheimer Drag extension to the fluid flow resistance in porous media flow has been added.
- It is now possible to include a convective term in the Brinkman Equations. This means that porous media flow including higher fluid velocity can be studied. The inclusion of the term is controlled using the Neglect inertial term (Stokes-Brinkman) switch available in the Brinkman Equations and the Free and Porous Media physics interfaces.
- Stabilization has been included for the Brinkman equations. The stabilization provides increased robustness and less computational cost for a given accuracy compared to previous versions. It is also imperative when solving problems including the convective term.
- A new Open Boundary condition is introduced in the physics interfaces for chemical species transport. The condition is designed to be used on model boundaries including both convective in and outflow sections. On sections with inflow the species concentration is not affected, while on sections with inflow a user defined exterior concentration is enforced.
- A new physics interface for Species Transport in Porous Media accounts for the effect of the tortuous path in porous media. This path results in the additional dispersion perpendicular to the main flow of a transported species caused by the convective flux. The dispersion of species in porous media is thus more accurately described compared to previous implementations.
- A new physics interface for Heat Transfer in Porous Media can be used to accurately study heat transfer in porous catalysts, filters, and other unit operations involving porous media.
Backward Compatibility vs. Version 3.5a
Pseudo Application Modes
The Pseudo application modes for species transport in version 3.5a allow for the use of the dependent variable for time as a space coordinate in the direction of the flow.
The corresponding physics interfaces are not yet implemented in version 4.0a. They are planned for 4.1.
Meanwhile, you can either create this alternative description manually, by relating time to a position along the length of the reactor using the axial velocity, or you can use a full 2D or 3D model.
Thin Boundary Layer Pair Boundary Conditions
The thin boundary layer approximation approximates the mass flux perpendicular to an interface according to:
where ni denotes the flux of species i, n the normal vector, cs the surface concentration, and cb the bulk concentration of species i.
In the case where cs actually is a concentration in a separate domain, so that the interface between two domains requires a discontinuous concentration but a continuous flux, this condition could be defined in 3.5a using pair boundary conditions.
Version 3.5a models using this functionality are not automatically converted to version 4.0a.
However, you can covert these models manually in version 4.0a by using separate fields for the surface and bulk concentrations. The analogy is also valid for heat flux.
Equilibrium Reactions and Mass Transport
The equilibrium reaction assumptions defined by entering in the Reaction Engineering interface does not automatically generate space-dependent formulations. This functionality will be implemented in a later version.