新型旋风分级器流场特性及颗粒分级性能

针对传统旋风分级器分级效率较低的难题，本文设计了一种中部进风、顶部重力进料式新型旋风分级器，利用数值模拟和试验手段对其流场特征及分级性能进行了研究。模拟结果表明，新型旋风分级器内存在若干旋涡，主气流进入分级器后形成由上、下两个旋涡构成的主分级流场，上部旋涡均为上行气流，下部旋涡为切流返转形式；二次气流形成的细颗粒淘洗旋涡具有近壁面处高转速、中心区快速上升的特点，最大轴向速度达16.5m/s，可强化对边壁处浓集颗粒的剪切分散和淘洗作用，对主分级流场切向速度影响较小，但可使其轴向速度值最大增加100%，这将缩短细颗粒的停留时间；主分级流场与淘洗流场相互作用形成分区流动，具有较明显的动态边界，为粗、细颗粒的定向分离提供了力场基础。试验表明，二次气量占比约20%，主、二次气流气速分别为14m/s和20m/s时，牛顿分级效率可达88%，分级精度指数K值最小为1.84，此时新型旋风分级器具有较高的分级精度。

Flow field characteristics and particle classification performance of a new cyclonic classifier

The traditional cyclonic classifiers with a top tangential air-solid inlet currently have low particle classification efficiency. For this problem, a new cyclonic classifier with middle tangential air inlets and feed tube was designed. The flow field characteristic and classification performance were investigated numerically and experimentally respectively. The simulated results showed that several vortexes were created in the classifier. The main flow was characterized by an upper upward vortex and a downer reverse-flow vortex. The secondary air formed another vortex with high tangential velocity near the wall and axial velocity at the center, which forms the washing effect for the fine particles mixed into the coarse fraction. The maximum axial velocity reached 16.5m/s. This secondary air enhances the dispersion of particles gathered near the wall due to the strong shear effect. The injection of secondary air had less effect on the tangential velocity of the main flow, but increased the central axial velocity with a maximum increasing rate of 100%. Thus the fine particle residence time chould be shortened. The primary and secondary air occupied the separated space with an obvious dynamic border despite of the air inlet velocities, which provided steady centrifugal field for the particle classification. The experimental results showed that the new classifier had a maximum Newton efficiency of 88% and the minimum K value of 1.84 when the secondary air volume accounted for about 20% of the total air volume and the primary and secondary air velocity was 14m/s and 20m/s respectively, indicating that the new cyclonic classifier has good classification performance.