Experimental investigation of mixing phenomena in a gas stirred liquid bath

Mixing phenomena in a room temperature water bath, agitated by injecting air through a straight circular nozzle fitted axially at the bottom of the vessel, were characterized by experimentally measuring mixing time(t _mix) by electrical conductivity technique. It was found thatt _mix defined at 99.5 pct homogenization did not depend on location and size of conductivity probe, location of tracer injection, and the amount of tracer injected. tpet decreased with increasing gas flow rate and bath height, but decreasing nozzle diameter. Visual observations of the two-phase plume and flow conditions in the bath revealed that the plume swirled above a certain gas flow rate which enhanced the mixing rates in the bath. The transitions in Int _mix vs In ε_b curves were found to correspond to onset of swirling; ε_b is the rate of buoyancy energy input per unit bath volume. Systematic analysis of experimental data revealed that a fraction of gas kinetic energy contributed to mixing in the bath. It was a function of bath height, being negligible at lower bath heights and almost 1 at larger bath heights. Further, it was experimentally found thatt _mix decreased with increasing bath height only up to a certain value, beyond which it started increasing. Visual observations of the bath revealed that the height at whicht _mix started increasing corresponded to a transition in which the bath was converted into a bubble column. The experimental data, for a particular bath height, were fitted into two separate straight lines of the formt _mix =cε ⁻ⁿ wherec andn are empirical constants and ε is the rate of energy input per unit bath volume. Formerly Graduate Student in the Department of Metallurgical Engineering at the Indian Institute of Technology, Kanpur, India