Experimental analysis of bubble velocity in a rotating fluidized bed

The bubble velocity in a two-dimensional rotating fluidized bed (RFB) was experimentally analyzed. The motion of bubbles was observed by means of a high-speed video camera, and the radial and angular components of bubble velocity were experimentally measured. The radial bubble velocity (UBr) and angular bubble velocity (ωB) were expressed as a function of actual centrifugal acceleration acting on the bubble (g′B)(g′B), bubble diameter (Db), and angular velocity of the rotating vessel (ωv): UBr=Kr(g′BDb)0.5UBr=Kr(g′BDb)0.5 and ωB = Kθωv, respectively. The effects of the operating parameters (gas velocity and centrifugal acceleration) on the bubble velocity coefficients (Kr and Kθ) were analyzed experimentally. The distribution of both bubble velocity coefficients could be well correlated by the log-normal distribution function. The distributions of Kr and Kθ showed almost unchanged with the gas velocity and centrifugal acceleration, because the buoyancy force acting on a bubble under high centrifugal force field is so high, and the interaction from other bubbles can be neglected. The bubble velocity coefficients in an RFB could be empirically obtained as Kr = 0.52 and Kθ = 0.96. The experimental mean bubble velocities at the various operating conditions were compared with the predicted ones by using the obtained bubble velocity coefficients and our proposed model for the bubble diameter [H. Nakamura, T. Iwasaki, S. Watano, Modeling and measurement of bubble size in a rotating fluidized bed, AIChE J. 53 (2007) 2795–2803]. The radial and angular bubble velocities could be predicted only by the operating parameters.