Influence of the Top Impeller Diameter on the Gas Dispersion in a Sparged Multi-impeller Stirred Tank

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• 作者：Yuyun Bao ; Jie Yang ; Lei Chen ; Zhengming Gao
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2012
• 出版时间：September 26, 2012
• 年：2012
• 卷：51
• 期：38
• 页码：12411-12420
• 全文大小：562K
• 年卷期：v.51,no.38(September 26, 2012)
• ISSN：1520-5045

文摘

The impeller configuration with a hollow half-elliptical blade dispersing turbine below two up-pumping wide-blade hydrofoils, identified as HEDT+2WH_U and recommended in previous work, was used in this study. The effect of the top impeller diameter, ranging from 0.33T to 0.50T, on gas鈥搇iquid flow in a stirred tank of 0.48 m diameter was investigated by experimental and CFD methods. Power consumption, total gas holdup, and local void fraction were measured for the impeller configurations with different top impeller diameters. Results show that while the ratio of top impeller diameter to tank diameter (D_top/T) increases from 0.33 to 0.50, the relative power demand (RPD) in a gas鈥搇iquid system decreases slightly. The increase of total gas holdup with rising gas flow rate becomes less evident as D_top/T increases from 0.33 to 0.50. Local void fractions at the measurement points above the height of 0.8T increase significantly with the increase of top impeller diameter. When D_top/T = 0.50, there is an extremely large voidage of about 50% just above the top impeller. The maximum voidage decreases with the decrease of top impeller diameter and almost disappears when D_top/T = 0.33. CFD simulation based on the two-fluid model along with the population balance model (PBM) was used to investigate the effect of top impeller diameter on the gas鈥搇iquid flows. The power consumption, total gas holdup, and local void fraction predicted by the CFD approach were in reasonably good agreement with the experimental data.