I have a pretty naive question, though imporant to me. Usually when solving the following PDE in solute transport:$\frac{{\partial C}}{\partial t } = \nabla. (D\nabla C -vC )=0$one can be ask to use a third-type boundary condition (called flux in software like Comsol or Phreeqc):$(D\nabla C -vC )=vCo$where the left side is assume to be the center of the cell and the right the inflow or outflow flux (Am I right about this last sentence?)In some software (Comsol) you do not have to specify Co, therefore I assume that in such cases the boundary condition is reduced to:$D\nabla C = 0$Is that true? Can such boundary condition be considered constant flux boundary conditon? Thanks.
Flux boundary condition in solute transport
boundary conditions;comsol