Heat and Mass Transfer in Fluidized Catalyst Beds

Heat and mass transfer constitute fundamentally important transport properties for design of a fluidized catalyst bed. Intense mixing of emulsion phase with a large heat capacity results in uniform temperature at a level determined by the balance between the rates of heat generation from reaction and heat removal through wall heat transfer, and by the heat capacity of feed gas. However, thermal stability of the dilute phase depends also on the heat-diffusive power of the phase (Section IX). The mechanism by which a reactant gas is transferred from the bubble phase to the emulsion phase is part of the basic information needed to formulate the design equation for the bed (Sections VII-IX). These properties are closely related to the flow behavior of the bed (Sections II-V) and to the bubble dynamics. 

Although gas bubbles ascending through the emulsion of fine catalyst particles are constantly splitting and coalescing (Sections II, III, and V), they are largely free of particles (H14, K13, T19). Such a bubble, may be pictured as essentially spherical, with the lower of its volume occupied 

It follows that as the bubble rises more quickly, the gas which emerges from its roof will penetrate outward a smaller distance before being swept downward i.e., the limit of penetration will be nearer to the bubble wall. The total volume enclosed by the limit of penetration is called the cloud. 

These physical pictures of bubble dynamics have been developed by Davidson and Harrison (D3), Murray (M46, M47), Pyle and Rose (P9), Rowe et al. (R17) and others. Jackson (Jl) considered that a mantle of bed with increased voidage exists near the roof of the bubble. Most of the work on fluid-mechanical theories of aggregative fluidization have been reviewed by Jackson (in D5). 

The radius of the cloud has been given by Davidson and Harrison (D3) 

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VI. Heat and Mass Transfer in Fluidized Catalyst Beds. 360... 

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