# Diffusion Coefficient

Written by Jerry Ratzlaff on . Posted in Geotechnical Engineering

Diffusion coefficient, abbreviated as D, also called diffusivity, expresses the transfer rate of a substance by random molecular motion.

## Diffusion Coefficient formula

 $$\large{ D = \frac{ 1 }{ \mu } \; \sigma \; T_a }$$

### Where:

 Units English Metric $$\large{ D }$$ = diffusion coefficient $$\large{\frac{ft^2}{sec}}$$ $$\large{\frac{m^2}{s}}$$ $$\large{ T_a }$$ = absolute temperature $$\large{F}$$ $$\large{K}$$ $$\large{ \sigma }$$  (Greek symbol sigma) = Stefan-Boltzmann constant $$\large{constant}$$ $$\large{ \mu }$$  (Greek symbol mu) = friction coefficient $$\large{dimensionless}$$