Numerical simulation of steady and transient mass transfer to a single drop dominated by external resistance

In a boundary-fitted orthogonal coordinate system, the general governing eq uations for steady and transient axisymmetrical cases of mass transfer in t he external region around single buoyancy-driven drops in steady motion und er low or intermediate Reynolds number were expanded and numerically solved by the control volume formulation. The simulation results for typical case s were presented and compared well with the data and empirical correlations in the literature. It suggests that the developed mathematical formulation of the external mass transfer for a deformable buoyancy-driven drop is rea sonable, and may give reliable simulating results. The analysis of the mass transfer coefficient against the detail of flow near the drop interface sh ed light to the respective contribution of molecular diffusion, convection and recirculating wake, as to provide information on the characteristic tim e scale of decaying Sherwood number, and hence, to be Valuable for analyzin g and optimizing the solvent extraction operation. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.