Solid Ion Model Reference

You use the Solid Ion model for modelling (or transporting) electrochemical species (such as charged ions) in a solid continuum or solid porous phase.

The electrochemical species can participate in an electrochemical reaction with a neighbouring fluid domain. For these cases, the Solid Ion model must be used in the solid continuum as a companion model to the Electrochemical Reactions model which is registered in the fluid domain.

Although it is possible to use the Solid Ion model in a shell region as a companion for the electrochemical reactions, the Solid Ion model does not transport / resolve profiles of molar concentration within the shell. This behavior is as expected for many cases in which thin shells are not able to develop pronounced differences in molar concentration. However, if gradients of molar concentration are expected, use a non-shell region.

Table 1. Solid Ion Model Reference
Theory	The Solid Ion model solves a transport equation for molar concentrations in the same way as the Electrochemical Species model (depending on the settings of the model properties). See Dilute Solutions. See Electrochemical Surface Reactions (Heterogeneous).
Provided By	Either: [physics continuum] > Models > Electrochemistry [solid porous phase] > Models > Electrochemistry
Example Node Path	Either: Continua > [physics continuum] > Models > Solid Ion Continua > [physics continuum] > Models > Porous Media > Porous Phases > [Porous Phase] > Models > Solid Ion
Requires	In a region: Space: any Material: Solid Optional Models: Electrochemistry In a solid porous phase: Material: Solid Optional Models: Electrochemistry
Properties	Key Properties are: Transport. See Solid Ion Model Properties.
Activates	Model Controls (child nodes)	Electrochemical Species Components. See Electrochemical Species Components Reference
	Boundary Inputs	See Boundary Settings.
	Other	Provides the ability to register multi-component liquid or multi-component gas species (as well as electrochemical species) as part of the electrochemical reaction mechanism for corresponding Reacting Surface models in liquid physics continua.

Solid Ion Model Properties

The following properties are available to specify when using the Solid Ion model—except in shell regions.

Convection

In transport equations, you can choose from a range of schemes that calculate the convection term at a cell face. This calculation requires Simcenter STAR-CCM+ to compute the face value of a quantity from the surrounding cell values. The method used for computing this face value has a profound effect on the stability and accuracy of the numerical scheme. For guidance on selecting a convection scheme, see Convective Flux.

1st-order: First-order convection scheme.
2nd-order: Second-order convection scheme.

Secondary Gradients

Neglect or include the boundary secondary gradients for diffusion and/or the interior secondary gradients at mesh faces.

On: Default value. Solves for interior and boundary types of secondary gradient.
Off: Does not solve for either type of secondary gradient.
Interior Only: Solves for the interior secondary gradients only.
Boundaries Only: Solves for the boundary secondary gradients only.

Electroneutrality option

Specifies if the overall ionic charge density is strictly enforced as zero or not. When simulating corrosion applications, maintain the default option (Scaling).

Not Enforced: Not Enforced is the default option when using the Electrostatic Potential model or Solid Ion model. A uniform zero ionic charge density is not enforced. However, depending on the setup of other parameters, the overall ionic charge density may already equal zero. This option is appropriate for non-corrosion related applications which do not require electroneutrality.
Scaling: Scaling is the default option when using the Electrodynamic Potential Model. This method ensures that the overall ionic charge density is equal to zero by scaling the ionic charge densities for each species proportionally. When the species have equal charge numbers, the total concentration is not changed by scaling. Simcenter STAR-CCM+ checks the concentration profiles that are set using the concentration dimension property and provides a warning if they are not electrically neutral. This option is appropriate for applications that feature electroneutrality, such as corrosion and etching. See Eqn. (4077).

Transport

Defines how the Electrochemical Species model / Solid Ion model is coupled to other models and so defines the transport equations that Simcenter STAR-CCM+ solves.

Species <> Electric Potential: Physical two-way coupling of flux contributions between the Electrochemical Species model / Solid Ion model and the Electric Potential model.
Electric Potential > Species: One-way coupling including drift flux / migrative contributions from the Electric Potential model to the Electrochemical Species model / Solid Ion model. The Electrochemical Reaction model does not enforce charge conservation.
Species > Electric Potential: One-way transfer of contributions from the Electrochemical Species model / Solid Ion model to the Electric Potential model.
- When using the Electrostatic Potential model, the contributions are for the space charge density.
- When using the Electrodynamic Potential model, the contributions are for the diffusive current.
No Electric Potential Coupling: The Electrochemical Species model / Solid Ion model and the Electric Potential model act independently. The Electrochemical Reaction model does not enforce charge conservation.

Note	If a charge is specified for one of the Solid Ion species, then to prevent a "Charge does not balance" error, set the Transport property to any option except Species <> Electric Potential.

Boundary Settings

The following boundary settings are available to specify when using the Solid Ion model—except in shell regions.

Wall Boundary

Wall Electrochemical Species Option

The wall electrochemical species option for a boundary allows you to define what happens at that boundary regarding electrochemical species.

Method	Corresponding Physics Value Nodes
Impermeable Specifies zero flux at the boundary.	None
Specified Flux You can specify the Value as a Constant or Composite array. The physics condition, Wall Electrochemical Species Flux Derivative Option also becomes available to specify.	One of the following nodes appears depending on what you set for Concentration Dimension on the Electrochemical Species model. You can specify the Value as a Constant or Composite array. Molar Concentration Flux Number Density Flux
Specified Value	One of the following nodes appears depending on what you set for Concentration Dimension on the Electrochemical Species model. You can specify the Value as a Constant or Composite array. Molar Concentration Number Density

Wall Electrochemical Species Flux Derivative Option

The Wall Electrochemical Species Flux Derivative Option allows you to specify the derivative of the Molar Concentration Flux of species

i

(or Number Density Flux) with respect to the molar concentration of species

i

(or number density) at the wall. The Concentration Flux Derivative represents:

\frac{d N_{n, s, i}}{d c_{i}}

and the Number Density Flux Derivative represents:

\frac{d N_{n, s, i}}{d n_{p}}

where

N_{n, s, i}

is the molar concentration flux of electrochemical species,

i

(or number density) at the wall,

c_{i}

is the molar concentration of electrochemical species

i

at the wall, and

n_{p}

is the number density at the wall.

This derivative is used for linearization.

This option is available when the Wall Electrochemical Species Option boundary condition is set to Specified Flux.

Method	Corresponding Physics Value Nodes
None The derivative of the Concentration Flux is not calculated. This is the default option.	None
Specified Allows you to specify the concentration flux derivative that is used for linearization.	Concentration Flux Derivative Allows you to specify the concentration flux derivative as a Constant or Composite array. For a stable set-up, make sure that the flux derivative has a negative value.

Interface Settings

The following interface settings apply to contact interfaces between a solid and a fluid region containing solid phases.

Electrochemical Species Phase Contact Option

Allows you to couple the electrochemical species defined in a solid region with the electrochemical species defined in the solid phase of a fluid region.

Available when you activate the Solid Ion model in both:

the physics continuum associated with the solid region
the phase models associated with the solid phase within the fluid continuum

Method	Associated Physics Value
None The interface is impermeable between all phases.	none
[Phase n] Available for each solid phase for which the Solid Ion model is activated. Couples the solid porous phase that you select with the solid region.	Electrical Resistance The electrical resistance at the interface between the solid region and the solid phase.