# Effective Diffusivity in Porous Media

Written by Jerry Ratzlaff on . Posted in Geotechnical Engineering

Effective diffusivity in porous media, abbreviated as $$D_e$$, is the adequate dispersion of gas or liguid through the voids of soil.

## Effective diffusivity in porous media formula

 $$\large{ D_e = \frac{ D \; n \; \delta }{ \tau } }$$

### Where:

 Units English Metric $$\large{ D_e }$$ = effective diffusivity $$\large{ \frac{ft^2}{sec} }$$ $$\large{ \frac{m^2}{s} }$$ $$\large{ D }$$ = diffusion coefficient in gas or liquid filling the pores $$\large{\frac{ft^2}{sec}}$$ $$\large{\frac{m^2}{s}}$$ $$\large{ n }$$ = porosity available for transportation $$\large{dimensionless}$$ $$\large{ \delta }$$  (Greek symbol delta) = constrictivity $$\large{dimensionless}$$ $$\large{ \tau }$$  (Greek symbol tau) = tortuosity $$\large{dimensionless}$$