Dear Moderator,

Thanks for your kind reply. I am afraid that the YCYLINDER coordinate system is not enough to model the problem, and I may not clearly explain what I am looking for help and the processes of the problem.

1)What I am looking for help?

A right coordinate system for directly modeling all equations 1, 9 and 10.

2) The processes of the problem

The problem describe pollutants in solution pass through column and also transfer into packed spheres. There are three consecutive processes defining the problem.

i) axial convection-diffusion transfer of pollutants through the packed area inside a column. In a differential section, Adz, as defined by equation 1, corresponding to this process with a constant DL,

ii) pollutants diffuse from bulk solution to the film around the spheres, and then migrate into the outer surface of spheres, which is called film diffusion and defined by equation 9 with a constant kf.

iii) pollutants transfer from their outer surface into the intra-pores inside, called intra-pore diffusion and defined by equation 10 with a constant Dp.

I expect to directly model all the three equations 1, 9 and 10 together and look for help on pointing out the right coordinate system.Restricted by the allowed size of the attachment, I can not upload a clear version describing the problem. Can I post a webpage URL here, which links to a clear PDF version and clearly defines the problem?

http://citeseerx.ist.psu.edu/viewdoc/do ... 1&type=pdf