Effect of Taylor vortices on mass transfer from a rotating cylinder

Abstract

AbstractMass transfer from solids, which has important applications in a number of chemical and pharmaceutical industries, has been studied experimentally and semiempirically under turbulent flow conditions, and correlations are available in the literature to calculate the mass‐transfer coefficients from pellets, rotating cylinders and disks etc. However, mass transfer under laminar flow has not been sufficiently addressed. One of the difficulties here is the strong Reynolds number dependence of the flow pattern, for example, due to the onset of Taylor vortices for the case of a rotating cylinder. This problem is circumvented by using a computational fluid dynamics (CFD)‐based solution of the governing equations for the case of a cylinder rotating inside a stationary cylindrical outer vessel filled with liquid. The parameters cover a range of Reynolds number (based on the cylinder diameter, and the tangential speed of the cylinder), Schmidt number and the ratio of the outer to inner cylinder diameters. The results confirm that the circumferential velocity profile is a strong function of the Reynolds number and varies from a nearly Couette‐type flow at very low Reynolds numbers to a boundary layer‐like profile at high Reynolds numbers. The onset of Taylor vortices has a strong effect on the flow field and the mass‐transfer mode. The calculations show that the Sherwood number has a linear dependence on the Reynolds number in the Couette‐flow regime, and roughly square‐root dependence after the onset of Taylor vortices. Correlations have been proposed to calculate the Sherwood number taking account of these effects. © 2005 American Institute of Chemical Engineers AIChE J, 2005