Modeling Ionic Species Flux

The Electrochemical Species model uses transport equations to solve the flux of ionic species in electrolytes.

Follow this procedure to model convection, diffusion, and migration of ionic species using the Electrochemical Species model. When modeling ionic species flux in a solid, only diffusion and migration are considered. This workflow does not include modeling reactions between electrochemical species—if you want to model electrochemical reactions involving ionic species, see Modeling Electrochemical Surface Reactions.

NoteA double precision version of Simcenter STAR-CCM+ is required to model the transport of electrochemical species when coupling the electrochemical species model with an electric potential model.

When modeling any electrochemical application, the Electrochemistry model is required. The Electrochemical Species model is also required for modeling migration of species. Further physics model selections depend on the application that you are modeling.

To model ionic species transport in an electrolyte:
  1. For the physics continuum that represents the electrolyte, select the following models, with Auto-Select recommended models activated:
    Group Box Model
    Space Select one.
    Time Select one.
    Material Select one of:
    • Liquid
    • Gas
    • Solid (required when using the Solid Ion model for a continuum)
    Flow Select either of:
    • Segregated Flow
    • Coupled Flow.
    Equation of State Constant Density
    Viscous Regime Select one.
    Optional Models Electrochemistry
    Electrochemistry Electrochemical Species
    Optional Models If you want to model ionic species flux in a solid porous phase, select Porous Media

    See Porous Media Models.

    Optional Models Electromagnetism
    Electromagnetism Select either of:
    • Electrodynamic Potential Select this model when simulating ionic species flux in applications such as corrosion or etching. See What Is the Electrodynamic Potential Model?
    • Electrostatic Potential (unavailable when the Porous Media model is selected). Select this model when simulating non-corrosion applications, especially if you want to model ionic charge densities or other setups which do not require electroneutrality. See What Is the Electrostatic Potential Model?
    Note
    • Use a liquid model for modeling corrosion applications.
    • The Electrochemical Species model does not support Multiphase models.
    • If you do not select an Electromagnetism model, the migration flux cannot be solved—only diffusion and convection flux are solved.
  2. Select any extra Optional Models that are required.
    • If the Electrostatic Potential model is already selected and you want to model the Coulomb force that is exerted due to non-zero ionic charge densities, select the Coulomb Force model. See Coulomb Force Solver.
    • If you want to set a constant temperature without solving an additional transport equation, select the Segregated Fluid Isothermal model. If no temperature model is selected, the Electrochemical Species model runs with a constant temperature of 293.15 K.
    • If you want to model ionic species flux in a solid continuum, select the Solid Ion model. Alternatively, to model ionic species flux in a solid porous phase, select the Solid Ion model in a porous phase.
  3. Click Close.
  4. Define the materials. Any fluid materials that you select for the electrolyte continuum act as a solvent for the electrochemical species which are assumed to be part of a dilute solution.
    See either:
  5. Specify the electrochemical species.
    1. Right-click the Electrochemical Species > Electrochemical Species Components node and select Select Mixture Components.
    2. Select all of the electrochemical species that represent the ionic species that are present in the electrolyte. If you cannot find a complex electrochemical species component, you can either:
      • Close the dialog, add electrochemical species to the database, then reopen the Select Mixture Components dialog, and select the species. See Modifying a Copy of the Material Database.
      • Select a similar electrochemical species component and modify its material properties to change the charge, and the type and quantity of atoms.
    3. Click Apply, then Close.
    4. To modify the composition or properties of an electrochemical species component, expand the Electrochemical Species Components > [Electrochemical Species Component] node and edit the Material Properties as required. See Electrochemical Species Components Reference.
    5. Expand the Electrochemical Species > Electrochemical Species Components node and for each of the Electrochemical Species Components, specify the Method for each Material Property.
      Certain material properties are specific to the Electrochemical Species model and allow you to define the properties of the ionic species directly. You can also define ionic species further under the Tools > Material Databases node.
Specify the method for solving the concentrations of the electrochemical species:
  1. Select the Electrochemical Species node and specify the Electrochemical Species Solver Option as Coupled or Segregated.
    The Segregated Electrochemical Species Solver runs faster than the Coupled Electrochemical Species Solver at low current densities. However, the Coupled Electrochemical Species Solver provides the best stability and is more capable of reaching convergence at high current densities than the segregated option. The Coupled Electrochemical Species Solver is not compatible with the Solid Ion model, it is intended for use with the Electrochemical Reactions model or the Bulk Ion Chemical Reactions model. If you use the coupled solver without these models, the runtime increases considerably without any benefit.
  2. If you use the Electrochemical Species model with the Electrodynamics Potential model:
    1. Expand the Models > [Material] > Material Properties node.
    2. Select the Electrical Conductivity node and set Method to Electrochemical Species.
  3. Define the region type and conditions. You can specify a fluid or porous region for the electrolyte continuum. However, when using the Electrochemical Species model, porous baffle interfaces are not allowed.
  4. Define the Initial Conditions. You can specify the Molar Concentration or Number Density of each electrochemical species as an initial condition for the electrolyte continuum. See Electrochemical Species Model: Initial Conditions.
  5. When modeling ionic species flux in a region, if necessary, you can define specific source terms to solve in the transport equations. This optional feature allows you to adjust the predefined source terms to suit the application that is being modeled. See Electrochemical Species Model: Region Settings.
  6. Define the boundary and interface conditions. See Electrochemical Species Model: Boundary Settings and Interface Settings.
    When simulating ionic wind:
    • To set zero space charge density and zero electric potential for the collecting electrode, set the boundary conditions for the collecting electrode as follows:
      • Set the Method for the Wall Electrochemical Species Option to Specified Value (the value is 0.0 by default).
      • Set the Method for Electric Potential Specification to Electric Potential (the value is 0.0 by default).
    • To specify the visual critical electric field for the discharge electrode, for the discharge electrode boundary, set the Method for Electric Potential Specification to Electric Potential and specify the corresponding Electric Potential value.
    • To specify zero ion flux at dielectric boundaries, set the Method for Electric Potential Specification to Specific Electric Flux (the value is 0.0 by default).
    See Surface Effects in Ionic Winds.
When modeling fluid regions that contain a solid phase (see Porous Media Models), you can define an interface between the solid phase and a solid region. At this interface, the solid phase can exchange ionic species and electric potential solution with the solid region. To define the interface:
  1. Activate the Solid Ion model and the Electrodynamic Potential model in both:
    • the physics continuum associated with the solid region
    • the phase models associated with the relevant solid phase. You define solid phases and their models in the fluid physics continuum, under the Porous Media model node.
  2. Define identical electrochemical species in the fluid and solid continua. The species must have identical names and properties.
  3. Create a contact interface between the fluid region that contains the solid phase and the solid region.
  4. Edit the Interfaces > [Solid/Fluid Interface] node and set the following properties:
    Node Property Setting
    Physics Conditions
    Electrodynamic Phase Contact Option Phase Select the solid phase that couples with the solid region.
    Electrochemical Species Phase Contact Option Phase Select the solid phase that couples with the solid region.
    Physics Values
    Electrical Resistance Value Specify the electrical resistance at the interface.
  5. Set up scenes and plots to visualize the solution.
    For example, you can visualize the following field functions in a scalar scene or plot them on an XY plot:
    • boundary specific electric current
    • electric current density
    • electric potential
    • charged species mobility of specific electrochemical species
    • migration flux of specific electrochemical species
    • molecular diffusivity of specific electrochemical species
    • molar concentration of specific electrochemical species
    • number density of specific electrochemical species
    See: Electrochemical Species Field Functions.
  6. Run the simulation.