The Effect of Secondary Flow in a Curved Pipe on Longitudinal Dispersion

Abstract

When a solute subject to molecular diffusion is convected by fluid in laminar flow through a tube it spreads out longitudinally and the mean cross-sectional concentration satisfies a diffusion equation, for large times, relative to a frame which moves at the mean speed of the flow. This fact leads to the definition of longitudinal diffusion coefficient. The present paper gives an expression for this coefficient in the case of a curved pipe. It is shown that in a curved pipe there is less longitudinal dispersion because of the increased lateral mixing due to the secondary flow.