Unsteady-state diffusion, convection, and chemical reaction in a fluid film (gas or liquid) obeys the following PDE:

,

where is the bulk flow velocity and is the diffusion coefficient of through the stagnant nondiffusing . The boundary conditions are

at ,

at ,

at .

This Demonstration plots the concentration profile of versus time and position in the fluid film for various values of the bulk flow velocity, diffusion coefficient and reaction rate constant.

You can try the following particular cases of interest:

: reaction and convection without diffusion

: diffusion and convection without reaction

: diffusion and reaction without convection