On the measurement of gas holdup distribution near the region of impeller in a gas–liquid stirred Rushton tank by means of γ-CT

Three flow patterns of flooding, loading and complete recirculation in a gas–liquid stirred Rushton tank were identified based on experimental observation. The gas–liquid system was composed of air and water. Under different operating conditions of gas flow rate and impeller rotating speed, the distribution of gas holdup near the region of impeller was measured using a γ-CT scan method. Both quantitative digital distribution curves of gas holdup and their qualitative color CT images were obtained. At the region of impeller, there was a convex characteristic peak of gas holdup distribution both in radial and in axial directions, and with the region being gradually away from the impeller, the distribution of gas holdup became flatter. The values of gas holdup in S33 regime were a little higher than those in L33 regime. Higher impeller rotating speed had some effect on the increasing of gas holdup at the region of higher axial height. The experimental measurement results were basically consistent with those previously published by Bombač. The hole number and diameter of sparger had little influence on the distribution of gas holdup, while the sparger's installed height had significant influence on them. When the sparger was installed close to the bottom of Rushton tank, a comparatively smoother distribution of gas holdup above the space of impeller could be obtained. The research results in this paper were useful for better understanding of gas holdup distribution near the region of impeller of Rushton tank, and could also provide experimental data for CFD simulation.

► Three gas flow patterns obtained from the current work are in good agreement with the flow regime map published before.
► Gas holdup distributions in ‘3-3’ regimes near the region of impeller were measured using γ-CT scan measuring technology.
► The CT images can accurately reflect the distribution of gas holdup.
► The hole number and diameter of sparger have little influence on the distribution of gas holdup, while the sparger's installed height has significant influence on them.