Bulk Mixing Using Diffused Air in Circular and Rectangular Vessels

Abstract

The use of compressed air for bulk mixing in circular and rectangular vessels has been investigated. A definition for “100% uniformity” has been postulated and correlations between the mixing time, shear gradient, and dimensionless diffuser submergence have been presented. It has been found that the mixing time in a vessel is primarily dependent on the shear gradient, G. A secondary dependence on the diffuser submergence is noted. Mixing times were measured using dye concentration versus time plots of salt and Rhodamine‐B dyes in batch experiments. Salt dye was found to produce longer mixing times for similar operating conditions. The product of the mixing time and the shear gradient has been calculated and compared to the values recommended in the literature for standard water and wastewater treatment operations. The writers' data fall below those recommended values, as expected, since only the time required for bulk uniformity and not chemical reaction, biological activity, floe formation, or gas transfer has been considered. A plot of the degree of uniformity versus the reduction in mixing time is presented. This allows for a reduction in operating time cost, for any degree of nonuniformity of the vessel contents.