Dispersive mass transfer, in fluid dynamics, is the spreading of mass from highly concentrated areas to less concentrated areas.
[1] Dispersive mass flux is analogous to diffusion, and it can also be described using Fick's first law: where c is mass concentration of the species being dispersed, E is the dispersion coefficient, and x is the position in the direction of the concentration gradient.
Dispersion can be differentiated from diffusion in that it is caused by non-ideal flow patterns[1] (i.e. deviations from plug flow) and is a macroscopic phenomenon, whereas diffusion is caused by random molecular motions (i.e. Brownian motion) and is a microscopic phenomenon.
Dispersion is often more significant than diffusion in convection-diffusion problems.
The dispersion coefficient is frequently modeled as the product of the fluid velocity, U, and some characteristic length scale, α: This fluid dynamics–related article is a stub.