If Convection is enabled on the interface top node, you can specify the Velocity field (m/s) as user-defined input using analytical expressions or the velocity field variables solved for by a separate physics interface.

The Electrolyte node automatically defines the concentration variables for protons (<name>.cH) and hydroxide ions (<name>.cOH), and the corresponding flux expressions.

In the Proton and Hydroxide Ion Transport Properties section you can modify the Diffusivity–mobility relation either by selecting the Nernst–Einstein relation (default) or entering values manually (No relation).

In the Water Self-Ionization section you can change the default Built in expression for the Water self-ionization constant, pKw (unitless), to any user-defined expression.