轴流桨搅拌槽内轴向流动速度的研究

Study of axial flow velocity in axially stirred tank

为研究轴流桨搅拌槽内轴向速度的分布,在直径为300 mm的平底圆筒搅拌槽内,采用相位多普勒粒子分析仪(PDPA)对轴流式搅拌器主流区的流场进行测量。在不同转速和离底间隙条件下,对挡板前轴向时均速度在径向和轴向的分布进行分析和研究,采用壁面射流理论,建立搅拌槽内壁面射流流动模型,揭示轴向流动特性。结果表明:轴向速度沿径向的分布具有相似性;轴向最大速度沿轴向衰减;轴向流边界沿轴向线性扩展。研究结果有助于进一步了解搅拌槽内部流动特性,为固-液悬浮操作、过程放大和搅拌设备的优化设计提供理论依据。

To study the distributions of the axial velocities of axial flow impeller stirred tank, the flow in the bulk flow field produced by an axial flow impeller was investigated in a flat bottomed cylindrical stirred tank with a diameter of 300 mm by using Phase Doppler Particle Analyzer （PDPA） measurement technique. The axial and radial distributions of the mean axial velocities were studied at many points in front of the baffle under different rotational speeds and off -bottom clearances. The wall-jet theory was applied to study the characteristics of the axial flow in front of the baffle. A simplified wall jet model in axially stirred tank was established. The results show that the radial profiles of the axial velocity component exhibit the similarity. The maximum values in upward flow decay with the increasing of the distance from the bottom of the tank. As flow moves upwards, the axial flow expands in radial direction. The results are useful for further understanding of the characteristics of bulk flow in a stirred tank, and provide the theoretical basis for solid-liquid suspensions, scale-up and optimal design of agitated equipment.