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 Solvent node automatically defines the concentration variables and for protons (<name>.cH) and hydroxide ions (<name>.cOH), and the corresponding flux expressions. See Diffusion and Migration Settings for how to set up the transport parameters for the proton and hydroxide ions.

In the Solvent Properties section you can modify the Dynamic viscosity (Pa·s) and Relative permittivity (unitless) values. The Built in and default values are applicable to water. These parameters are used when calculating mobilities according to the Debye–Hückel–Henry relation in the species nodes.

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.