Study on a New System of Multi-stage Classification using an Almost Rigidly Rotating Flow

我们研究了一种新的湿式离心式分级系统，它采用了几乎刚性旋转的流动。这种流动由地转内部区域、非地转Stewartson层和Ekman层和/或刚性旋转区组成。在这个离心机系统中。由于离心力和流体阻力的大小不同，可以任意增大离心力而不产生任何湍流波动，很好地控制离心力和流体阻力，因此可以将悬浮在低浓度水中的极细颗粒准确地划分为粗颗粒和细颗粒。因此，该系统适用于精确的亚微米分级。在本研究中，我们处理了一个可以同时将饲料颗粒分为粗、中、细三种产品的双级系统，作为多级系统的基础。对间歇式和半连续式的分级性能进行了实验研究。由此，我们得出如下结论，其中离心力参数表征了作用在颗粒上的离心力与流体阻力之比。(1)半连续型(细粒和中等产品均可连续获得)的中间产物的质量中值直径略大于间歇型(只有细粒可连续获得)，但质量中值直径较小。(2)在间歇型和半连续型中，随着离心力参数的增加，中间产物的质量中值直径和变异系数变小。即中间产物的粒度变得更细小、更均匀。(3)在单级分级性能上，有萃取级的分级精度略低于无萃取级。

We have studied a new wet-type centrifugal classification system that employs an almost rigidly rotating flow. This flow consists of geotropic interior regions, ageostrophic Stewartson and Ekman layers, and/or a rigid-rotation region. In this centrifugal system. we can accurately classify very fine feed-particles suspended in water with a low concentration into coarse and fine products by the difference in the centrifugal force and fluid drag exerting particles due to the difference in particle size, because we can increase the centrifugal force arbitrarily without producing any turbulent fluctuation and well manage the centrifugal force and the fluid drag. Hence, this system is adaptable to an accurate submicron classification.In the present study, we have treated, as the basis of the multi-stage system, a double-stage system that can classify feed particles into coarse, medium and fine products all at once. we have experimentally investigated the classification performance of both batch and semi-continuous types. Consequently, we have drawn the following conclusions, where a centrifugal-effect parameter characterizes the ratio of the centrifugal force acting on a particle to the fluid drag.(1) the semi-continuous type (both fine and medium products are obtainable continuously) shows a slightly greater coefficient of variation of the medium product than the batch type (only a fine product is obtainable continuously), but shows a smaller mass median diameter.(2) In both batch and semi-continuous types, with increasing centrifugal-effect parameter, the mass median diameter and coefficient of variation of the medium product become smaller, i.e. the medium product becomes finer and more uniform in particle size.(3) On the classification performance of each stage as a single-stage classifier, the stage with extraction shows a slightly worse classification accuracy than that without extraction.