用电导探针测定气-液多层桨搅拌槽内气泡尺寸分布

Bubble Size Distributions Measurement in a Gas-Liquid Multi-Impeller Stirred Tank by Using Dual-Conductivity Probe

在直径0.48 m的椭圆底三层组合桨搅拌槽中,使用双电导探针测定常温24℃及热态81℃通气条件下,空气-去离子水体系的局部气泡尺寸分布,分别利用标定法及数学重构法进行数据处理,得出适宜方法为数值解析的重构法。采用以半椭圆管盘式涡轮(HEDT)为底桨,上两层分别为四叶轴流桨下压(WHD)及上提(WHU)操作的HEDT+2WHD及HEDT+2WHU组合桨,测定槽内沿径向和轴向的气泡尺寸分布。结果表明:采用HEDT+2WHU的气泡尺寸较HEDT+2WHD大,在底桨附近及上层桨以上区域气泡尺寸差异较大;平均气泡直径前者约为后者的1.13倍。热态时气泡尺寸分布规律与常温相近,但气泡尺寸显著增大:热态与常温相比,采用下压及上提组合桨时全槽气泡直径平均值分别增加29%及26%,结果与文献吻合良好。

In a multi-impeller stirred tank with 0.48 m diameter,the local bubble size distributions（BSD） in the sparged air-water system were measured at 24℃ and 81℃ by using the dual electric conductivity probe.The agitators including a hollow blade dispersing turbine below and two down-pumping or up-pumping hydrofoils above were identified as HEDT＋2WHD and HEDT＋2WHU,respectively.Both the calibration method and reconstruction model were used to convert the measured bubble chord length to the bubble size.The results show that the bubble sizes of using HEDT＋2WHU are larger than those of HEDT＋2WHD,and the difference is obvious in the regions near the bottom impeller and above the top impeller.The average bubble size of using HEDT＋2WHU is 1.13 times of that of using HEDT＋2WHD.The BSD measured at 81℃ is similar as that measured at room temperature 24℃,but the average Sauter bubble size measured in hot system by using HEDT＋2WHU is about 29% greater than that measured in cold system;and when using HEDT＋2WHD,the average Sauter bubble size measured in hot system is about 26% greater than that measured in cold system.The measured bubble size values are in good agreement with those predicted by using the correlation published in literature.