Effect of surface roughness and form drag

Gamson et al have successfully used the y-factor method to cocrelate titeir experimental results for heat and mass transfer between a bed of granular solids and a gas stream. 

4 Mass trans from a fluid to the surfiaee of parties 

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 heat 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 analyticai 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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