Porosity and Kinematic Diffusivity
 

Hi, I have a problem. I am trying to set up a kinematic diffusivity variable, but with different values of porosity (Two subregions). Basically what I want is :

Porosity= a for z<=zo

Porosity= b for z>zo

Since Kinematic Diffusivity = Porosity*Binary Diffusion

Binary diffusion is taken from an empirical formula. Any ideas?

Thank you

Luis