Mass transfer in aerated vibrated beds

Abstract

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.