涡流空气分级机转笼结构对分级性能的影响
本文选题:涡流空气分级机 + 转笼内外半径 ; 参考:《北京化工大学》2015年硕士论文
【摘要】:粉体物料的分级是粉体材料生产过程中重要的单元操作之一,涡流空气分级机则是该单元操作中经常使用的一种分级设备。随着粉体技术的发展,对粉体分级设备的要求越来越高,因此对分级机的改进研究一直在进行。分级机的内部结构是影响分级性能的重要因素,近年来对其结构的优化研究取得了显著的成果,为分级机的结构改进提供了理论基础。本文主要从转笼内外半径的尺寸以及转笼叶片间距的大小两方面对涡流空气分级机的结构进行改进,采用FLUENT对改进前后的涡流空气分级机内部流场进行了数值模拟,得到了使环形区以及转笼叶片间流场稳定的转笼内外半径尺寸以及转笼叶片间距,并对转笼内外半径改进前后的涡流空气分级机进行了物料实验以验证模拟结果。为研究转笼叶片宽度不变时,转笼内外半径对涡流空气分级机分级性能的影响,采用FLUENT对具有不同内外半径转笼的涡流空气分级机内部流场进行模拟,模拟结果表明:转笼内外半径同时减小18 mm,环形区宽度增加18 mm时,环形区气流切向速度增大,有利于物料的分散,切向速度在单位宽度内的变化率由0.208 m·s-1·mm-1减小到0.149m·s-1·mm-1,说明环形区流场分布的均匀性有所提高;同时转笼入口附近切向速度波动从2.7 m·s-1减小到O.8 m·s-1,进入转笼的细粉产品的粒径分布变窄;此时,由于转笼叶片间距减小,使得叶片间惯性反旋涡强度明显减弱,径向速度分布均匀,细粉能够迅速进入转笼内部实现分级,降低了细粉颗粒返混到粗粉的可能性,使分级精度提高。碳酸钙物料实验表明:转笼内外半径同时减小18mm时,分级精度提高3.3%-25.4%,同时细粉产率增加27.8%-76.2%,物料实验结果与模拟结果相符。转笼叶片数的改变使叶片间距发生变化,在转笼内外半径一定的情况下,存在一个使叶片间流场最稳定的转笼叶片间距。对不同转笼在不同叶片间距下的流场进行研究表明:当叶片间距与叶片宽度之比为0.23时,叶片通道内的径向速度分布最均匀;对颗粒在不同间距的叶片通道中的运动轨迹进行模拟后发现,当叶片间距与叶片宽度之比为0.23时,颗粒在叶片通道内的运动轨迹简单,且不易与叶片壁面发生碰撞,细颗粒能够快速地进入转笼内部实现分级,避免了细粉颗粒的返混,能够明显提高分级精度。
[Abstract]:The classification of powder materials is one of the important unit operations in the production of powder materials, and the eddy current air classifier is a kind of classifying equipment which is often used in the unit operation. With the development of powder technology, the requirement of powder classifier is more and more high, so the improvement of classifier has been carried out all the time. The internal structure of the classifier is an important factor affecting the performance of the classifier. In recent years, remarkable achievements have been made in the optimization of the classifier's structure, which provides a theoretical basis for the structural improvement of the classifier. In this paper, the structure of swirl air classifier is improved from the dimensions of the inner and outer radius of the cage and the distance between the blades of the rotary cage. The internal flow field of the swirl air classifier before and after the improvement is numerically simulated by FLUENT. The size of the inner and outer radius of the rotating cage and the distance between the rotor blades are obtained to stabilize the flow field in the annular region and between the blades of the cage. The material experiments of the swirl air classifier before and after the improvement of the inner and outer radius of the cage are carried out to verify the simulation results. In order to study the influence of the inner and outer radius of the cage on the classification performance of the swirl air classifier, the flow field of the swirl air classifier with different inner and outer radii was simulated by FLUENT. The simulation results show that when the inner and outer radius of the rotating cage decreases 18 mm and the width of the annular region increases 18 mm, the tangential velocity increases in the annular region, which is beneficial to the dispersion of materials. The change rate of tangential velocity in the unit width is reduced from 0.208 m s -1 mm-1 to 0 149 m s -1 m m -1, which indicates that the uniformity of the flow field distribution in the annular region has been improved. At the same time, the tangential velocity fluctuation near the inlet of the cage decreases from 2.7 m s ~ (-1) to O. 8 m ~ (-1), and the particle size distribution of the fine powder product entering the cage becomes narrower. At this time, due to the decrease of the rotor blade spacing, the strength of the inertia counter-vortex between the blades is obviously weakened. The radial velocity distribution is uniform, the fine powder can quickly enter the inner of the cage to realize the classification, which reduces the possibility of the fine powder particles mixing back to the coarse powder, and improves the classification accuracy. The experiment of calcium carbonate material shows that when the inner and outer radius of the cage is reduced simultaneously, the classification accuracy is increased by 3.3- 25.4and the yield of fine powder is increased by 27.8-76.2.The results of the material experiment are in agreement with the simulation results. The change of the number of rotor blades makes the blade spacing change. In the case of a certain radius inside and outside of the cage there exists a rotor blade spacing which makes the flow field between the blades the most stable. The flow field of different cages with different blade spacing is studied. The results show that when the ratio of blade spacing to blade width is 0.23, the radial velocity distribution in the blade passage is the most uniform. After simulating the movement trajectory of particles in the blade passage with different spacing, it is found that when the ratio of blade spacing to blade width is 0.23, the particle movement path in the blade passage is simple, and it is not easy to collide with the blade wall. The fine particles can quickly enter the inner of the cage to realize the classification, avoid the backmixing of the fine particles, and can obviously improve the classification accuracy.
【学位授予单位】:北京化工大学
【学位级别】:硕士
【学位授予年份】:2015
【分类号】:TQ051.8
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