Rushton桨搅拌槽内平均流场的二维PIV试验研究

用粒子图像测速技术(Particle image velocimetry,简称PIV)对带有Rushton桨叶的,无挡板搅拌槽内的流场进行研究。在叶轮转速240 r/min下,流动的雷诺数Re=1 527时,获取了桨叶处以及桨叶转过5个不同角度处的粒子图像。在对粒子图像进行处理和计算后,得到了相平均速度场和系综平均速度场,并给出了速度分布剖面图。结果表明,所研究的Rushton桨搅拌槽内径向喷射流动沿桨叶垂直方向是非对称的,而是向下方倾斜。在桨叶附近,径向流动速度高。随着流动远离桨叶,径向速度在降低。因此径向喷射流动作用就相当于自由射流:叶轮桨叶喷射出的流体进入周围大量低速运动的流体中,卷吸周围流体,并沿轴向和径向扩散,从而使更多的流体参与混合和反应。所作研究对于深入了解搅拌槽内流场结构具有实际意义。

TWO-DIMENSIONAL PIV EXPERIMENTAL INVESTIGATION OF MEAN FLOW FIELD IN STIRRED TANK WITH RUSHTON TURBINE

Particle image velocimetry(PIV)technique is used to study the flow field in stirred tank with Rushton turbine and without baffles. Particle images are captured at six different blade positions under the conditions of rotating speed and Reynolds number being 240 r/min and 1 527, respectively. By processing and calculating the particle images, phase-averaged and mean velocity fields are obtained, and the velocity distribution profiles are also presented. The results shows that the im-peller stream of the Rushton turbine is not symmetrical, but skewing downwards. Closing to the impeller tip, the radial velocity is higher than other parts. Away from the blade tip, radial velocity is getting smaller and smaller. Therefore, the impeller stream behaves like a free jet: the fluid is ejected from the impeller blades into a mass of slowly-moving fluid and it spread out vertically and entrains a considerable amount of surrounding fluid into it outer parts and make more fluid mix and react.