Breakage Time of Bubble in a Stirred Tank for Different Impeller Geometries, An Experimental Investigation

The successful tank stirring operation requires extensive studies for selecting a suitable impeller design for the dispersion processes in such systems. In this context, the effects of impeller geometry and Reynolds number (Re) on bubble breakage time were investigated to gain a deeper understanding of the breakage phenomena. Three different impeller geometries were investigated: a 4-Twisted blades impeller (4TB), a 4-Flat blades impeller (4FB), and a 2-Flat blades impeller (2FB) For Re range of 18380 to 40830 (based on impeller diameter). Three different time intervals were recognized during the mother bubble’s motion; initial breakage time, final breakage time, and retention time. The initial and final breakage times were calculated by following the injected bubble using a high speed camera at different zones around and in the impeller region. It was found that the breakage time decreases with increasing Reynolds number (or stirring speed) for all geometries. The 4-Flat blades impeller showed the lowest breakage time indicating the highest breakage rate. For 4-FB impeller, it decreases by about 20% when the Re increases from 18380 to 40830. The breaking interval increases with increasing Re and is lowest for 4FB impeller. The increase is for 4FB is 65%.