A new approach to the identification of transitions in fluidized beds

Earlier work with silica sand has indicated that in a system where a bed of particles is aerated at increasing superficial velocities, the von Neumann ratio, T, based on the bed pressure drop, may be useful in identifying both minimum fluidizing velocity, Umf, and minimum bubbling velocity, Umb. Plots of T− 1 against superficial velocity exhibited significant change at velocities consistent with those where bed height first changed (onset of fluidization), the packed bed pressure drop underwent a transition from a monotonic linear function of superficial velocity to a steady value (onset of fluidization) and standard deviation of bed pressure drop rapidly increased (onset of bubbling). However, the suggestion that T might be a valid indicator of Umf was supported by data for a single material only. In this paper additional data is presented that supports the suggestion that T might be useful in measuring Umf, and also provides additional evidence for the potential utility of T in determining Umb. In principle, this would allow a single campaign of pressure measurements to be used to identify both Umf and Umb.