.

with the following boundary conditions:

at , ,

at , ,

Here is the pore length and is the surface concentration of species . The second boundary condition specifies that there is no flux of material through the interior end of the cylindrical catalyst pores. The concentration of reactant within a pore is given by , where is the Thiele modulus and .

This Demonstration plots the dimensionless concentration versus the dimensionless distance within the pores for user-set values of the Thiele modulus. It also gives the value of the effectiveness factor , where is the average concentration of species in the catalyst pores.