Particle movement due to bubble motion

Based upon these observations, Rowe (1977) derived an expression for the average particle circulation time t around a bed in terms of excess gas velocity and bed height at minimum fluidization 

Although this expression may not accurately predict circulation time, and in any case particles do not follow a simple predetermined circuit around the bed, it serves to illustrate the significance of the excess gas velocity in determining particle mixing rates. The excess gas flow rate, proportional to the excess gas velocity, is essentially the bubble flow rate. A greater bubble flow generates more bubbles and therefore 

Parficle mixing is covered at greater length in Chapter 2. 

Generally the pressure drop across the plate should be high to promote even gas distribution and is usually some fraction of the pressure drop across the fluidized bed porous distributors tend to have much higher pressure drops than other types of plate. 

Porous or sintered plates are the ideal and are used in small-scale studies of fluidized bed behaviour (Kunii and Levenspiel, 1991) and form a highly expanded unstable gas-solid dispersion directly above the distributor which rapidly divides into a large number of small bubbles plus an emulsion phase. Bubbles grow rapidly thereafter by coalescence. Kunii and Levenspiel (1991) also suggest that other 

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