Corrosion Module Updates
For users of the Corrosion Module, COMSOL Multiphysics® version 5.3 includes a new Current Distribution, Shells interface, a new Current Distribution, Boundary Elements interface, and a new physics interface for modeling chemical species transport in fractures. Learn more about these and more Corrosion Module updates here.
Current Distribution, Boundary Elements Interface
The Current Distribution, Boundary Elements interface can be used for solving primary and secondary current distribution problems on geometries based on edge (beam or wire) and surface elements. The interface uses a boundary element method (BEM) formulation to solve for the charge transfer equation in an electrolyte of constant conductivity, where the electrodes are specified on boundaries or as tubes with a given radius around the edges. You typically use this interface in order to reduce the meshing and solver time for large geometries, where a significant part of the geometry can be approximated as tubes along edges.
A ship is anchored close to an oil platform. The ship hull is subjected to the electric field from the cathodic corrosion system. The figure to the left shows an insulated hull, for example insulated by a thick paint.
Current Distribution, Shell Interface
The Current Distribution, Shell interface models ionic current conduction in the tangential direction along a boundary. The physics interface is suitable for modeling thin electrolytes where the potential variation in the normal direction is negligible, for instance, in atmospheric corrosion problems. Here, a very thin electrolyte film may form on metal surfaces. The interface allows you to consider the ionic current without having to mesh this liquid layer in 3D.
Ion-Exchange Membrane Internal Boundary Condition in the Tertiary Current Distribution, Nernst-Planck Interface
The new Ion-Exchange Membrane boundary node specifies a boundary condition where the flux of ions is continuous, but where the electrolyte potential is discontinuous and is described by a Donnan equilibrium. This condition is typically used in electrochemical cells containing both free electrolytes and ion-exchange membranes, for instance, in dialysis problems. A Donnan potential shift over the interface is calculated automatically from the concentrations of the charge-carrying ion on each side of the interface.
Electrolyte potential in a vananadium redox flow battery showing the potential shifts at the interfaces between the free electrolyte and the ion-exchange membrane.
Application Library path for the updated Vanadium Redox Flow Battery model:
New Charge Conservation Models in the Tertiary Current Distribution, Nernst-Planck Interface
The Tertiary Current Distribution, Nernst-Planck interface now supports four different charge conservation models: electroneutrality, water-based with electroneutrality, supporting electrolyte, and Poisson.
Thin Electrode Layer Functionality
The Thin Electrode Layer feature can be used to model a thin insulating or resistive sheet, located on an internal boundary in an electrode domain. The functionality can be used as an alternative to drawing the actual layer domain in the model geometry, which significantly reduces meshing and solution time, especially in 3D models. A thin electrode layer can be used to model, for instance, a contact impedance between two electronic conductors. The layer may be set to be either insulating or resistive.
Thin Electrolyte Layer
The Thin Electrolyte Layer feature specifies a thin electrolyte layer on an internal boundary between two electrolyte domains. The node can be used as an alternative to drawing the actual layer as a domain in the model geometry in order to significantly reduce meshing and solution time. The condition may be set to either insulating, resistive, or ion-exchange membrane. This feature replaces the Thin Insulating Layer feature in earlier versions.
Circuit Terminal Condition
You can use the Circuit Terminal feature on a boundary to specify a coupling to the External I Vs. U node in the Electrical Circuit interface from the AC/DC Module. The Circuit Terminal condition is now also available as a boundary condition in the Electrode Surface node and as an operation mode in the Single Particle Battery interface. This allows you to include high-fidelity battery models in circuit simulations.
New Transport of Diluted Species in Fractures Interface
Fractures have thicknesses that are very small compared to their length and width dimensions. It is often difficult to model the transport of chemical species in such fractures through having to mesh the thickness of the fracture surface, due to the aspect ratios brought about by the large differences in size dimensions. The new Transport of Diluted Species in Fractures interface treats the fracture as a shell, where only the transverse dimensions are meshed as a surface mesh.
The interface allows you to define the average fracture thickness, as well as the porosity in cases where the fracture is considered to be a porous structure. For the transport of the chemical species, the interface allows definition of effective diffusivity models to include the effects of porosity. Convective transport can be coupled to a Thin-Film Flow interface or through including your own equations to define fluid flow through the fracture. Additionally, chemical reactions can be defined to occur within the fractures, at its surfaces, or in a porous medium that encompasses the fracture.
Fracture Surfaces in the Transport of Diluted Species in Porous Media Interface
In cases where transport occurs in a fractured, porous 3D structure, the new Fracture boundary condition lets you model transport in the thin fractures without having to mesh them as 3D entities. The Fracture boundary condition is included in the Transport of Diluted Species in Porous Media interface (see image) and has the same settings as in the Transport of Diluted Species in Fractures interface (described above). Fluid flow and chemical species transport are seamlessly coupled between a 3D porous media structure and fluid flow and chemical species transport in a fracture.
The image below shows the concentration field in a porous reactor model. In the model, a twisted fracture "leaks" reactants deeper into the porous catalyst, from left to right, at a faster rate than the transport through the porous media. This is because the fracture surface has a much higher average porosity compared to the surrounding porous catalyst, which gives a higher mass transport rate.
New Electrophoretic Transport Interface
The new Electrophoretic Transport interface can be used to investigate the transport of weak acids, bases, and ampholytes in aqueous solvents. The physics interface is typically used to model various electrophoresis modes, such as zone electrophoresis, isothachophoresis, isoelectric focusing, and moving boundary electrophoresis, but is applicable to any aqueous system involving multiple acid-base equilibria.
Zone electrophoresis separating a mixed sample of two proteins into two well-resolved concentration peaks.