Abstract
Detailed power consumption characteristics from experiments and simulations of gas–liquid stirred tanks with shear-thinning power-law liquids are presented. The motion of bubbles was investigated based on the Euler–Euler approach with a bubble cluster concept. The drag coefficient of bubbles with a constant bubble diameter was modeled as the Schiller and Naumann function. The predicted power consumption of a gas–liquid mixture shows reasonable agreement with experimental data with a maximum deviation of 8.9%. For the studied aerated systems, a qualitatively new power reduction correction equation was derived and demonstrated a reasonable agreement with experimental results compared with the literature-reported equations. The effect of the concentrations and gas flow rates on power consumption was presented. It was found that the power consumption of different mixtures is related to the change in the critical generalized Reynolds number, which was Reg = 440, 230, 100, 30, and 25 for 0.2%, 0.4%, 0.62%, 0.85%, and 1.25%, respectively.
Highlights
Gas–liquid flow in stirred tanks is widely used in chemical and biological processes, such as waste-water treatment, chemical reactions, and biomass fermentation, owing to its good contact between the phase and liquid stirring
The results indicated that the vortex clinging structure appearance of one and two large cavities and ragged cavities was recognized by the frequency transformation of the time-domain structure–function
It is concluded that gas could be escaped from the tank with higher gas flow rates when the impeller is at a lower rotation speed
Summary
Gas–liquid flow in stirred tanks is widely used in chemical and biological processes, such as waste-water treatment, chemical reactions, and biomass fermentation, owing to its good contact between the phase and liquid stirring. Liu et al. investigated the gas–liquid power consumption and mass transfer distribution characteristics with the help of computational fluid dynamics (CFD) as a function of gas superficial velocity, liquid superficial velocity, and magnetic field strength It concluded that the increased gas flow rate and reducing surface tension result in improved gas–liquid mass transfer performance. Wei et al. investigated the two-phase flow based on the single-phase simulation flow field and obtained good predicted results They utilized a CFD model implemented with the population balance model (Sauter mean bubble diameter) to simulated gas hold-up and the gas–liquid mass transfer coefficient of a 3 l stirred vessel by using a pitched blade impeller. In contrast to modeling an ungassed mixer with Newtonian and non-Newtonian fluids, studies regarding experimental and numerical simulations of gassed power reduction characteristics that result from the gas–liquid and cavity structures behind the curved impeller blades are not found in the open literature.. An attempt was made to develop a new correlation equation to model the power characteristics between gassed and ungassed cases, which was validated with the experimental results and literature correlations
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