1 2 0 = entry condition d = dense phase = as seen 10 cm above distributor = as seen 25 cm above distributor = bubble diameter, m = concentration of reactant A, mol/m3 = acceleration due to gravity, m/sz = height at which bubble is fully formed, m = reaction rate constant from packed bed data, s-l = bubble frequency, Hz = volumetric gas flow rate into expanded dense phase, = volumetric gas flow rate through orifice, m3/s = bubble radius, m = rate of reaction of A, mol/m3.s = bubble formation time, s = bubble equilibration time, s = bubble rise velocity, m/s = minimum fluidization velocity, m/s = visible bubble volume, m3 = fraction of orifice flow forming a visible bubble = dense-phase voidage = dense-phase voidage at minimum fluidization m3/s ACKNOWLEDGMENTS We are grateful to the following students who carried out this experimental work as part of a course on gas fluidization: [This manuscript is dedica fed to the memory of C. Y. Wen]The behavior of bubbles in a cocurrent gas-liquid-solid fluidized bed was in-AKlNORl MATSUURA and LIANG-SHIH FAN Department of Chemical EngineeringThe Ohio State Unlversity Columbus, OH 43210 vestigated in a column of 76.3 mm ID in this study. The particles used were glass beads of 3 and 6 mm and a binary mixture of these particles. A novel dual electrical resistivity probe system was developed and utilized to obtain bubble properties including bubble size and rise velocity. The distributions of the bubble properties in the gas-liquid-solid fluidized bed were evaluated for three flow regimes: the dispersed bubble flow regime; the coalesced bubble flow regime; and the slug flow regime. SCOPEGas-liquidsolid fluidized beds have been fully developed and demonstrated in processing technology; as three-phase reactors, they have been employed in the H-oil process for hydrogenation and hydrodesulfurization of residual oil, the H-coal process for coal liquefaction, and the biwxidation process for waste water treatment.A knowledge of hydrodynamics is of considerable importance in design and operation of a gas-liquid-solid fluidized bed. Among various hydrodynamic properties, bubble size and rise velocity and their distributions are of prime concern, as they are directly responsible for the behavior of other hydrodynamic properties such as liquid flow patterns, solids mixing, and gasliquid interfacial area.Very limited information is available in the literature regarding the in-bed bubble size or rise velocity distributions in the gas-liquidsolid fluidized bed. Page and Harrison (1972) used photographic techniques to examine the size distribution of bubbles leaving a gas-liquid-solid fluidized bed and found that the logarithmic cumulative distribution function varies linearly with bubble size. Using an impedance double-probe, Darton and Harrison (1974) reported that bubble size in a three-phase fluidized bed of 500 pm sand particles follows a lognormal distribution.This study is directed toward a fundamental understanding of in-bed bubble properties including bubble size and bubble rise veloci...

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The axial dispersion in the liquid-phase of a gas-liquid down flow through a packed column was studied with air and water flowing concurrently in a 8.0 cm diameter column with glass spheres of 0.12, 0.26 and 0.43 cm.The impulse response was calculated numerically from the two signals measured at two crosssections in the bed. The response was characterized by both a peak and a very long tail, and could be represented satisfactorily by using the PDEmodel in which the mass transfer between the dynamic and the stagnant holdups in addition to the axial dispersion in the dynamic holdup was taken into account. Four parameters appearing in the PDEmodel were determined by means of the time domain curve fitting method. Peclet number which was based on the actual velocity in the dynamic holdup ud had a constant value of 0.43 for ReX=udpdvl» < 150, increased with Re' and attained another constant value of1.7 for Re >400.The volumetric mass transfer coefficient was correlated as a function of particle size, liquid and gas velocities. The total liquid holdup agreed well with the literature data. The fraction of the dynamic holdup varied in the range of 0.6 to 0.95 depending on the particle size and the gas and the liquid velocities. The correlation of the dynamic liquid holdup was given graphically.

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