过渡流搅拌槽内单颗粒悬浮特性的实验研究

Experimental study of single particle suspension in transitional flow in a stirred tank

利用高速摄像技术对过渡流搅拌槽内单颗粒的运动特性进行捕捉,分析了搅拌雷诺数及桨叶离底高度对颗粒悬浮运动的影响规律,并使用二维粒子图像测速技术得到搅拌槽内的流场信息。研究结果表明:颗粒的临界悬浮转速随桨叶离底高度的降低而降低,桨叶离底高度对颗粒在槽底的运动影响较大,颗粒在垂直离底悬浮后,于桨盘下方附近螺旋上升或作持续的螺旋状圆周运动,搅拌雷诺数升高对颗粒垂直上升的最大高度和最大速度影响较小,但会减小垂直上升过程中桨盘的转动圈数,颗粒螺旋上升是由于轴向流场在颗粒停滞位置向两侧产生了分叉,颗粒的悬浮主要是由流体的主体流动引起的。

The characteristics of a single particle suspension under transitional flow in stirred tank have been investigated using high speed camera technology,and the effects of varying Reynolds number and the off-bottom clearance on particle suspension were analyzed.The flow field in the stirred tank was obtained by two-dimensional particle image velocimetry.The results show that: the critical impeller speed of a single particle decreases with decreasing off-bottom clearance;the off-bottom clearance has a great influence on the particle rolling over the bottom;the particle spiral upwards or makes a circular motion under the rotating disk after particle lift off;an increase in the Reynolds number has a minor effect on the maximum height and velocity of the vertical rise of the particle,but decreases the number of rotations of the impeller;the reason for the spiraling motion of the particle is that the axial flow creates a diversion to both sides at the hovering position of the particle;the suspension of the particles is caused by the mean flow of the fluid.