A vibrated bed is a mobile layer of solid particles contained in a vessel that is vertically vibrated. When a flow of gas is maintained through it , the bed is called an aerated vibrated bed and a vibrated gas-fluidized bed if the gas stream is greater than the minimum fluidization velocity of the particles. Mass transfer rates from solid particles coated with naphthalene to a nitrogen stream, the fluidizing gas, are determined using a gas chromatographic technique. Two kinds of coated beads of different densities are used: Master Beads and low-density glass beads. The investigation is done using a cylindrical vessel with bed depths of 24 mm, 12.7 mm, and 1 mm (ultra-shallow bed). A range of solid particles from 125 to 841 microns of geometric mean size is employed. Using a vibrational frequency of 25 Hz, the particle bed is vibrated at different intensities up to four times the gravitational acceleration. Vibrations increase the mass transfer rate to some extent depending on the bed depth. The mass transfer process is more important in shallow beds, where strong solid mixing occurs, than in deeper beds, where bulk-circulation patterns affect the naphthalene sublimation. Higher mass transfer rates are obtained with larger as well as heavier particles. / Master of Science

A vibrated bed is a mobile layer of solid particles contained in a vessel that is vibrated vertically. This study investigates bed dynamics and heat transfer from a vertical surface in shallow vibrated beds in absence of aeration. In general, "shallow" means a depth-to-width ratio less than one. In this study, bed depth is 30 mm, and this ratio is about 0.2. All experiments are at 25 hertz and at vibrational amplitudes affording peak accelerations between 2 and 7 times gravity. The study uses spherical glass beads of two densities and "Master Beads," nearly spherical particles of a crude, dense alumina, in size fractions from 63 to 707 micrometers. A disc embedded in the vessel floor, vibrated at 4.5 kilohertz, gives data on bed-vessel separation, showing it to occur later than predicted by plastic, single-mass models. The delay is attributed to bed expansion, monitored by piezoelectric force gauges mounted on floor and wall of the vessel. In large-particle beds, bed-vessel collision occurs simultaneously everywhere. In small-particle beds, exhibiting an uneven top surface, collision occurs first at the side walls and moves toward the center. In small-particle beds, pressure gradients appearing during the bed's free flight drive a horizontal component of particle circulation from the vessel's side walls toward its center. An apparent viscosity of the bed, estimated crudely by pulling a rod through it, influences this component's velocity. In beds of large particles, circulation is almost entirely vertical, a layer of two or three particles moving downward at a wall, and a slow return flow moving upward elsewhere. The study confirms the downward wall motion to be driven by friction. Heat transfer closely follows trends in rate of circulation. Greater dependence upon vibrational intensity is seen in small-particle beds. Values as high as 578 W/m²-K are measured. Comparison of vertical-surface heater geometry with an earlier horizontal tube shows the former to be generally superior for surface-to-bed heat transfer. / Ph. D.