COMSOL 6.4 - Transport of Diluted Species

In the Model Builder window, under Component 1 click Transport of Diluted Species

In the Settings window for Transport of Diluted Species, locate the Domain Selection section and in the Selection list choose Orange.

The orange pulp is quiescent so convection can be ignored in the model. Additionally, due to the presence of a lot of other ions in the pulp, acting as supporting electrolyte, we assume the potential gradients to be small and hence also ignore the effect of migrative transport of the zinc ions. Under Transport Mechanisms uncheck the checkboxes for Convection and for Migration in electric field

Electrode Surface Coupling I

For this example we will use the default diffusion coefficient value in the Transport Properties node so no settings are needed on the default domain node. The following steps couple the electrochemical reaction currents to the ion flux at the electrode surface.

In the Physics toolbar, click Boundaries

and choose Electrode Surface Coupling

in which the coupling can be enabled.

In the Settings window for Electrode Surface Coupling, locate the Boundary Selection section and in the Selection list select Zinc nail.

Reaction Coefficients I

In the Model Builder window, expand the Electrode Surface Coupling 1 node and click the Reaction Coefficients 1

node.

In the Reaction Current Density section, the iloc list setting should be that of the Zinc nail. Therefore, choose Local current density, Electrode Reaction 1 (cd/es1/er1).

In the Stoichiometric Coefficients section, enter In the n text field type 2, and in the νc text field type -1. These stoichiometric coefficients refer to the stoichiometric number of the reacting species when written as a reduction reaction.

Initial Values I

The initial zinc ion concentration at the start of the time-dependent simulation is required.

In the Model Builder window, under Component 1 and Transport of Diluted Species click Initial Values 1

Locate the Initial Values section and enter c_Zn20 in the c text field.

The node sequence of the interfaces in the Model Builder should now look like this: