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Go to Editorial ManagerThe hydrodynamics of stirred tanks and bubble breakup are crucial in gas-liquid flows, yet this system has not been well characterized for different operating conditions. In this work, the numerical method was used to investigate the hydrodynamics of six- flat blades impeller (Rushton turbine) and the results were employed to understand the bubble breakup behavior in the stirred tank. Simulation results of predicted flow pattern, power number, and the distribution of turbulence energy generated were performed with COMSOL Multiphysics. Numerical results showed good agreement with the experimental literature. The effect of rotational speed on bubble breakup behavior, such as breakage probability, the average number of daughter bubbles, and the breakage time was investigated using the high-speed imaging method. The main finding is that the breakage process occurs in the high energy area of high turbulence intensity, which is located within a distance equal to the blade width of a radius of (15-35 mm). The breakage probability (Bp) was found to be increased by 12.61 percent for a mother bubble of 4 mm at 340 rpm, with an average fragmentation of up to 22 fragments. Furthermore, the bubble breakage time was found to decrease with increasing impeller rotational speed, with an average value of 19.8 ms.
An experimental study on single bubble breakage in the stirred tank in oil as a continuous phase was carried out for a range of stirring speeds (220 to 430 rpm). The results are compared with bubble breakage in water that was conducted by Hasan et al. (2021) to investigate the effect of physical properties of continuous phase on the breakage rate. The breakage events in the impeller were captured and analyzed using a high speed camera. It was found that the breakage rate represented by breakage probability and a number of produced daughter bubbles (fragments) are directly proportional with the stirring speed. The breakage probability and number of produced daughter bubbles in oil was noticeably lower than that in water indicating the role the continuous phase viscosity plays in reducing the breakage rate.