In the Pre-Analysis step, we'll review the following:
Since we are neglecting the convection terms, the diffusion equation we want to use looks nearly identical to the heat equation. Therefore, we can solve the heat equation with the flow terms disabled and then simply reinterpret the results as if we had solved the diffusion equation.
The outer boundary will be set to “wall.” Then we will set a temperature boundary condition of 1, which corresponds to concentration as we discussed earlier.
Please see the hand out below for more details: