Abstract:

Feed areas of cyclonic classifier was divided according to air velocity distribution characteristics. The effects of three representative feed positions on particle trajectory and classifying accuracy was investigated and force on 1 μm and 10 μm particles in different areas was analyzed by unsteady discrete particle model and classification experiments. Near-wall feeding mingled fine particle into coarse powder and impaired classification accuracy. Near-center feeding exerted strong centrifuge force on coarse particles and high axial shear force on fine particles by high flow field intensity which reduced particle residence time in classification zone and achieved rapid classification with improved classification efficiency. Center feeding extended classification move distance of coarse particles and increased possibility of coarse particles going into fine fraction, which simulation showed that 11.7% of 15 μm coarse particle by mass was mixed with fine powder. Experimental results showed that near-center feeding at inlet air velocity in a range of 10 m·s^-1 to 22 m·s^-1 minimized overlap between distribution curves of coarse and fine particles and increased average ratio of classified particle diameter by 25.3%. Those results could provide guidance to design feed position of air cyclonic classifiers.

Key words: powder technology, cyclonic classifier, feed position, numerical simulation, particle size distribution

摘要：

根据旋风分级器内气流速度分布特点进行了进料区域划分，运用非稳态离散相模型和分级实验对比了3个代表性进料位置对颗粒运动轨迹及分级精度的影响，分析了1 μm和10 μm颗粒在不同区域内的受力情况。结果表明，边壁区域进料造成粗组分中细粉夹带现象严重，分级精度差；中部进料区域内流场强度大，粗颗粒受离心力强，细颗粒受轴向气流曳力大，有利于减少颗粒在分级区的停留时间，实现粗、细颗粒的快速分级，对改善分级精度有利；中心位置进料延长了粗颗粒的分级运动路程，增加了粗组分跑损的概率，模拟计算15 μm的粗颗粒进入细组分的质量分数达到11.7%。经实验验证，入口气速在10～22 m·s^-1，中部区域进料时分级后粗、细组分粒度分布曲线重合区面积最小，分级粒径比率值平均提高了25.3%，研究结果为离心气流分级设备的进料位置设计提供了一定的指导。

关键词: 粉体技术, 旋风分级器, 进料位置, 数值模拟, 粒径分布