In the present work, a γ-ray attenuation technique was used to measure gas holdup distribution in stirred tanks. Measurements have been carried out in a 0.57-m-i.d. tank agitated by a pitched blade downflow turbine (PBTD45°) and a disk turbine under two different conditions, namely, surface aeration and sparger aeration beneath the impeller. The measurements have been made at various operating speeds. In both the cases, the average gas holdup calculated by integration of the local gas holdup was found to match well with those obtained by visual observations based on volume expansion. The gas holdup profiles also enable identification of speeds of regime transition. This technique appears to be promising for the characterization of industrial stirred reactors.

In the present work, mixing time measurements have been made with jet mixers over a wide range of jet velocities, liquid levels and tank sizes. The nozzle was kept along the axis of the vessel and the nozzle clearance was varied over a wide range. It was observed that the mixing time decreases with an increase in the jet path length (nozzle clearance) for a given tank size and given amount of liquid. The reasons for this behaviour are explained with the help of CFD modelling. The effect of tank diameter has been studied independent of the jet path length. A correlation has been developed for process design. Jet mixers have been compared with impeller‐stirred tanks in terms of their energy efficiency. Reasons for the observed behaviour have been provided.