Regime Transition and Identification

In bubbling fluidization, bubble motion becomes increasingly vigorous as the gas velocity increases. This behavior can be reflected in the increase of the amplitude of the pressure fluctuations in the bed. With further increase in the gas velocity, the fluctuation will reach a maximum, decrease, and then gradually level off, as shown in Fig. 9.16. This fluctuation variation marks the transition from the bubbling to the turbulent regime. 

The onset velocity of the transition to the turbulent regime is commonly defined to be the gas velocity corresponding to the peak, Uc, whereas the leveling point, Ub, may be recognized as the onset of the turbulent regime proper [Yerushalmi and Cankurt, 1979]. 

Examining the variation of bubble behavior across Uc, a criterion for the bubbling-turbulent regime transition is proposed by Cai et al. (1992) as 

to predict the onset velocity for the regime transition using Eq. (9.48), a mechanistic model accounting for NB for a given fluidized bed operation is needed (Problem 9.9). 

The specific flow and transport characteristics of turbulent fluidization, which are distinctly different from those of bubbling fluidization operated at relatively low gas velocities, 

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