Air Entrainment Phenomenon due to a Free Falling Power Jet

自由落体动力射流引起的空气夹带现象

• 批准号: 09650195
• 负责人: TOMITA Yuji
• 金额: $ 1.92万
• 依托单位: KYUSHU INSTITUTE OF TECHNOLOGY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1997
• 资助国家: 日本
• 起止时间: 1997 至 1998
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650195/
• 关键词: Multi-phase flow; LDV; Powder jet; Air Entrainment; Numerical simulation; Terminal setting velocity; Axial velocity profile; Spreading width; LDV計測; ガラスビーズ; 落下速度; 半径方向速度; 数密度

When powder is discharged from the bottom orifice of vessel under gravity, the ambient atmosphere is entrained into the powder jet. in this research, we experimentally and numerically examine the flow mechanism of the free falling powder jet. A laser Doppler velocimeter is used for the measurement. The particles used are glass beads with a mean diameter of 454 mum .It is found that the free falling velocity of the powder jet is larger than that of the single particle in the still air and increases with an increase in the mass flow rate of powder. This is because there exists a downward air stream in the powder jet by the entrained air. At a long distance from the orifice, the velocity profile of powder jet relative to the local free falling velocity of the single particle is similar to that of a single-phase free turbulent jet. Near the orifice a potential-like profile is observed. Based on the present measurement we estimate the axial velocity profile of powder jet and the entrained air flow rate. The spread of the powder jet is very small as compared with that of the single-phase turbulent jet. The numerical simulation is performed based on Lagrangian modeling for particles and Eulerian modeling for air flow. We consider particle-particle collision, drag force, gravity force and transverse force due to the particle spin and to the velocity gradient of air flow, and apply a laminar flow model. The present simulation well explains our measurement in terms of particle and air velocity profiles and jet spreading.

当粉末在重力作用下从容器的底部孔口排出时，环境大气被夹带到粉末射流中。本文通过实验和数值模拟研究了自由下落粉末射流的流动机理。激光多普勒测速仪用于测量。所使用的颗粒是平均直径为454 μ m的玻璃珠。它被发现，粉末射流的自由下落速度大于单个颗粒在静止空气中的自由下落速度，并随着粉末的质量流量的增加而增加。这是因为在粉末射流中存在由夹带空气引起的向下的空气流。在离喷孔较远的地方，粉末射流相对于单个颗粒局部自由下落速度的速度分布与单相自由湍流射流的速度分布相似。在孔口附近观察到类似电势的轮廓。在现有测量的基础上，我们估计了粉末射流的轴向速度分布和夹带空气流量。与单相湍流射流相比，粉末射流的扩散范围很小。基于拉格朗日模型的颗粒和欧拉模型的空气流动进行数值模拟。考虑了颗粒间的碰撞、阻力、重力以及由于颗粒旋转和气流速度梯度而产生的横向力，并采用层流模型。目前的模拟很好地解释了我们的测量颗粒和空气的速度分布和射流传播。