Abstract:

The separation efficiency of cyclone separator for fine particles under 5 μm needs to be improved. In this paper, the concentration distribution of 1 μm particles in cyclone was studied by Reynolds stress model and stochastic trajectory model. The results showed that fine particles were gathered in the annular region where the upstream and quasi-free vortex overlap, forming a concentration peak. By analyzing the radial distribution of particles at different axial positions and at different times, it was found that there were two formation mechanisms. Firstly, the mismatch between the height of separation space and the nature vortex length led to the vortex end sweep the particles on the wall, resulting in a strong backmixing of particles. Then, backmixing particles moved outward due to the separation effect of internal swirl. The other mechanism was the convergence effect of downward flow entrained fine particles. Moreover, the former contributed more to the formation of particle concentration peak. Most of the particles in the dense ring would continue to move outward during running up, and then they would be separated by the external swirling flow again after entering the downflow. A few particles escape due to the entrainment of upflow or short-circuit flow. Inhibition of particle backmixing is the key to ameliorate particle dense ring. It can be achieved by optimizing the height or the internals.

Key words: cyclone separator, centrifugation, particle, concentration distribution, motion trajectory, computational fluid dynamics

摘要：

旋风分离器对5 μm以下颗粒的分离效率有待提高。通过雷诺应力模型和随机轨道模型研究1 μm颗粒在超高旋风分离器内的浓度分布。结果表明细颗粒在上行流和准自由涡的重叠区聚集，形成浓度高峰。分析不同轴向位置和不同时刻的颗粒径向分布，发现其形成机制有二：一是高度与自然旋风长不匹配导致旋涡尾端扫壁，引起大量颗粒返混，然后在内旋流的分离作用下向外移动；二是下行流向心汇聚对细颗粒的裹挟作用。机制一对颗粒浓峰的贡献更大。大部分浓环颗粒在上行过程中会继续外移，汇入下行流后再次经受外旋流的分离作用，少部分颗粒在上行流或短路流的裹挟下逃逸。抑制颗粒返混是改善颗粒浓环的关键，可通过优化高度或增加内购件的方式实现。

关键词: 旋风分离器, 离心分离, 颗粒, 浓度分布, 运动轨迹, 计算流体力学