(304j) On Modification of Mass Transfer Theories Using Finite Speed Diffusion

Different mass transfer theories that can explain the observations in the mass transfer correlations from experimental data such as the film theory, Higbie's penetration theory, Dankwerts surface renewal theory, Dobbins model, surface stretch theory and boundary layer theory were outlined. The generalized Fick's law of mass diffusion was used to modify the results from the penetration and surface renewal theories. The Fick's law of diffusion was found to violate the Onsager microscopic principle of reversibility. There are six reasons to seek a generalized Fick's law of diffusion (Sharma, 2006). The dimensionless group Sharma number was introduced. Sha = (k(tr)/a). Sharma number can be seen to be Sha = (ka/D)(Dtr/a^2 ) which is a product of the Sherwood number and the Maxwell number (mass). It gives the ratio of the mass transfer in bulk to the relaxational transfer during acceleration of molecules. A general 4 step procedure for the design of the different mass transfer operations is described. These are the construction equilibrium line from thermodynamics, operating line from mass balance, rate efects lumped into a parameter called efficiency and stage calculations in sequence. 26 different mass transfer operations are classified according to the nature of the interface.