Mass transfer from a fluid to the surface of particles

4 Mass transfer from a fluid to the surface of particles 

It is necessary to calculate mass transfer coefficients between a fluid and the surface of a particle in a number of important cases, including  

There have been comparatively few experimental studies in this area and the results of different workers do not always show a high degree of consistency. Frequently, estimates of mass transfer coefficients have been made by applying the analogy between heat transfer and mass transfer, and thereby utilising the larger body of information which is available on heaL transfer. 

Interest extends from transfer to single particles to systems in which the particles are in the form of fixed or fluidised beds. The only case for which there is a rigorous analytical solution is that for heat by conduction and mass transfer by diffusion to a sphere. 

Mass transfer from a single spherical drop to still air is controlled by molecular diffusion and. at low concentrations when bulk flow is negligible, the problem is analogous to that of heat transfer by conduction from a sphere, which is considered in Chapter 9, Section 9.3.4. Thus, for steady-state radial diffusion into a large expanse of stationary fluid in which the partial pressure falls off to zero over an infinite distance, the equation for mass transfer will take the same form as that for heat transfer (equation 9.26)  

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