Conditions under which dispersion of a solute in a stream of solvent can be used to measure molecular diffusion

Abstract It is shown that an assumption made in the author’s previous discussion (Taylor 1953) can be presented as a result of analysis. The conditions under which an approximate solution of the equations for diffusion in a moving fluid can be used to interpret longitudinal dispersion of a solute in a stream of solvent flowing through a tube is given as 4L/a - a Ua /D 6.9. Here U is the mean velocity, a the radius of the tube, D the coefficient of molecular diffusion. L is the length of tube over which appreciable changes of concentration occur.