Basic Research of a New Classification System using an Almost Rigidly Rotating Flow

本文研究了一种新型的湿式离心分级机，它是在一个由壳体和芯体组成的旋转双层壁容器内，利用几乎刚性旋转的通流进行分级。1. Ekman层中分类性能的理论研究（1）得到了Ekman层中粒子运动轨迹的近似解。(2)当各种粒径的进料颗粒在靠近堆芯壁处均匀进料时，切割粒径取决于流动的埃克曼数和罗斯比数（旋转和通流速率），壁梯度和曲率，以及颗粒的真实相对密度和形状，但锐度指数与这些参数无关。2.用二氧化硅颗粒进行亚微米分级的实验考虑（1）当Rossby数≥ 100时，E是8.1*10 - 4<-3>，锐度指数取决于埃克曼数E，并且对于E=6.7*10 - 4获得1.47的高锐度指数值<-5>。(2)3<1.70><-6>.粗粒回收用于连续分级的理论和实验研究（1）当回收率低于<CE>Ekman输运理论分析所得到的阈值K_（1/2）时，锐度指数几乎与不回收时一样好。(2)当抽拉速率大于K_<CE>时，在低于取决于Ekman数和Rossby数的临界抽拉速率K_时，尖锐度指数也很好<CS>，但在高于K_时，尖锐度指数变得很差<CS>。

We have studied a new wet-type centrifugal classification using an almost rigidly rotating through-flow within a rotating doubled-walled container consisting of a housing and a core. Consequently, we have obtained the following main results.1.Theoretical consideration on the classification performance in an Ekman layr(1) We obtained an approximate soluiton of particle trajectories in the Ekman layr.(2) When the feed particles of all sizes are unifomly fed near the core wall, the cut size depends on the Ekman and Rossby numbers of flow (rotation and through-flow rates), the wall gradients and curvatures, and the true relative density and shape of particles, but the sharpness index is independent of these parameters.2.Experimental consideration of sub-micron classification using silica particles(1) When the Rossby number epsilon_E is 8.1*10^<-3>, the sharpness index depends on the Ekman number E,and a high sharpness index value of 1.47 is obtained for E=6.7*10^<-5>.(2) The cut size is propotional to E^<1.70>, and the sub-micron classification is realized for E*6.0*10^<-6>.3.Theoretical and experimental considerations on the withdrawal of coarse particles for application to a continuous classification(1) When the withdrawal rate is below a threshold value K_<CE> obtained by the theoretical analysis of an Ekman transport, the sharpness index is almost as good as in a no-withdrawal case.(2) On the otherhand, when the withdrawal rate is above K_<CE>, the sharpness index is also good below a critical withdrawal rate K_<CS> depending on Ekman and Rossby numbers, but it becomes extremely bad above K_<CS>.