Diffusion – Diffusion is a mass transfer process whereby a solute is transported through a liquid under a concentration gradient. The diffusivity of a solute is defined as the mass of solute transferred per unit time across unit cross-sectional area under a unit concentration gradient. The diffusivity of a solute increases with temperature and reduction in molecular size. At ambient temperatures diffusion is not usually a rapid process and is often accelerated by agitation and by raising the temperature. Due to the parabolic velocity profile of a liquid flowing through a cylindrical tube radial transfer by diffusion can be very slow indeed. It can, however, be enhanced by deforming the regular shape of the cylindrical tube by pinching, coiling or bending and thus introducing radial mixing.

Further Information on this Topic can be found in the books of R.P.W. Scott by following the listed links