Mass transfer between flowing fluid and sphere buried in packed bed of inerts

Abstract

The equations describing fluid flow and mass transfer around a sphere buried in a packed bed are presented, with due consideration given to the processes of transverse and longitudinal dispersion. Numerical solution of the equations was undertaken to obtain point values of the Sherwood number as a function of the Peclet and Schmidt numbers over a wide range of values of the relevant parameters. A correlation is proposed that describes accurately the dependence found numerically between the values of the Sherwood number and the values of Peclet and Schmidt numbers. Experiments on the dissolution of solid spheres (benzoic acid and 2-naphthol) buried in packed beds of sand, through which water was forced, at temperatures in the range 293 K to 373 K, gave values of the Sherwood number that were used to test the theoretical results obtained. Excellent agreement was found between theory and experiment, including the large number of available data for naphthalene-air, and this helps establish the proposed correlation as "general" for mass transfer between a buried sphere and the fluid (liquid or gas) flowing around it. (C) 2004 American Institute of Chemical Engineers