reaction inside the porous particle

michael

hi, i do have my own model for reactive combustion where reactant is diffusing inside the pores within the porous coal particle and the process has the concentration and the temperature coupled second order differential equations d2c/d2r+2/r*dc/dr+R=0 and same for the temperature.my diffusivity,porosity and particle diameter are changing with time and temperature as well.i do have some functions for diffusity as well as porosity.is it possible to implement time and temperature dependent porosity in Fluent?if it is so then how i can make this ? is there any predefined model for such kind of problem ? any help would be appreciated by heart.. thanx