Chemical Engineering Science, Vol.100, 120-136, 2013
Effect of turbulence on particle and bubble slip velocity
In multiphase systems involving a dispersed phase, such as fluidized beds, the interphase exchange of mass, heat and momentum transfer can be very different from those from a single particle, droplet or bubble system under terminal conditions. Such differences need to be correctly predicted for proper design of multiphase reactors. However, most existing methodologies still rely heavily on empirical relationships for parameters such as slip velocity, especially for systems operating under turbulent conditions where there is wide difference in the reported results. In this study the hindered settling/rising (slip) velocity of single steel particles (d(PD)=5-12 mm) and single air bubbles (d(B)=1-4 mm) has been measured in a solid-liquid fluidized bed of uniform size borosilicate glass beads (d(P)=5 and 8 mm) as a function of liquid superficial velocity. The homogeneity and intensity of the turbulence within the fluidized bed has been quantified and directly related to the slip velocity of the foreign (steel or bubble) particle. It was found that the turbulence resulted in an increase in the computed drag coefficient for all of the experimental conditions investigated. (C) 2013 Elsevier Ltd. All rights reserved.