固液搅拌槽内桨叶启动过程中的两相流动特性

将折射率匹配技术与粒子图像测速技术结合，测量了固液搅拌槽内桨叶启动过程中的两相流动特性。实验所用搅拌槽为平底方槽，搅拌桨为45°四斜叶桨，桨叶搅拌雷诺数389~2 332，固体颗粒的最大体积分数15%。实验考察了桨叶操作方式、搅拌转速和固含率对搅拌槽内瞬态颗粒分布和颗粒床层处瞬时流场的影响规律，结果表明：相同转速下桨叶为上提操作时流体对颗粒床层的侵蚀作用强于下压操作，颗粒开始悬浮的时间早，但悬浮高度较低；随着搅拌转速的增加，流体对颗粒床层的侵蚀作用增强，体系达到稳态后搅拌槽内颗粒云的均一度和高度也出现上升趋势；固含率从5%增加至15%时，搅拌槽内悬浮起的颗粒数量增加；流体侵蚀颗粒床层的临界速度范围在0.1~0.25 m/s。

Characteristics of solid-liquid two phase flow during the start-up process of solids suspension in a stirred tank

Particle image velocimetry measurements combined with careful refractive index matching have been used to measure the instantaneous flow characteristics of a solid-liquid system in the start-up period of the suspension process. The experiments were carried out in a flat bottom square tank agitated by a 45° pitched blade turbine. The impeller-based Reynolds number was fixed in the range 389-2 332, and the maximum volume fraction of solids was 15%. The effects of varying the operating mode, impeller speed and solid volume fraction on the instantaneous particle distribution and flow field around the granular bed were investigated. The results showed that when the impeller speed is constant, the erosion by fluid on the granular bed in the upward mode is stronger than that in the downward mode, but the maximum height of the suspended particles in the former mode is lower than that in the latter mode. With increasing of impeller speed, the erosion effect of the fluid acting on the granular bed is enhanced. The homogeneity and the height of the particle cloud also increase when the system is fully developed. The number of suspended particles increases when volume fraction of solids is raised from 5% to 15%. The critical velocity required for the fluid to erode the granular bed is around 0.1-0.25 m/s.