Mass Transfer in Multiparticle Gas-Solid Systems

Substituting the corresponding values for the spouted bed into Eqs. (12.32), (12.68), and (12.69) reveals that the distance required for the gas to travel to achieve a thermal equilibrium with the solids in the annulus region is on the order of magnitude of centimeters, while this distance in the spout region is one or two orders of magnitude larger. 

Compared to the fluidized bed, a spouted bed with immersed heat exchangers is less frequently encountered. Thus, the bed-to-surface heat transfer in a spouted bed mainly is related to bed-to-wall heat transfer. The bed-to-immersed-object heat transfer coefficient reaches a maximum at the spout-annulus interface and increases with the particle diameter [Epstein and Grace, 1997]. 

Since the solid particles in the spouted bed are well mixed, their average temperature in different parts of the annulus can be considered to be the same, just as in the case of a fluidized bed. The maximum value of the heat transfer coefficient in the h-U plot is also similar to that in a dense-phase fluidized bed [Mathur and Epstein, 1974]. 

Values of the mass transfer coefficient for multiphase systems depend on the model which defines this coefficient. Hence, mass transfer coefficients should be used in conjunction with the corresponding model equations. 

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