Experimental investigation of air entrainment in free-falling particle plumes
Experimental investigation of air entrainment in free-falling particle plumes
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DOI：
10.1080/02726350701484006
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发表时间：
2007-01-01
影响因子：
2.5
通讯作者：
Wypych, P. W.
中科院分区：
文献类型：
--
作者：
Liu, Z.;Cooper, P.;Wypych, P. W.
粉末和颗粒状固体广泛用于工业散装固体储存、处理和运输系统中。这种散装材料处理操作经常涉及材料的下落流。在这样的过程中，周围的空气被诱导与下落的颗粒流一起流动，形成颗粒驱动的羽流。在这里，实验研究结果报告在这个基本问题上，特别是集中在由自由下落的颗粒夹带的空气的速度分布。研究表明，诱导空气的速度分布可以模拟为高斯分布。颗粒羽流的半径被发现线性增加，增加下降的高度，它也随着增加散装固体质量流量。与其他夹带流，如射流和羽流进行了比较，发现空气夹带，因此颗粒驱动的羽流的传播角度远小于其他夹带流。例如，粒子驱动羽流的传播角在1.3度< theta（s）< 1.8度范围内，而热源产生的混溶羽流的theta（s）约为5.7度。此外，中心线速度的诱导空气中的颗粒羽流被发现显着增加与增加下降的高度。从高速数字视频记录的结果表明，散装材料并不以均匀的方式膨胀，因为它的福尔斯，和一系列不同的粒子云的核心形成的粒子驱动的羽流。这些云最终在足够大的下落高度上消散。
Powders and granulated solids are widely used in industrial bulk solids storage, handling, and transportation systems. Such bulk materials handling operations frequently involve a falling stream of material. During such a process, the surrounding air is induced to flow with the falling particle stream, forming a particle-driven plume. Herein, experimental research results are reported on this fundamental problem, focusing in particular on the velocity profile of air entrained by the free-falling particles. This investigation shows that the velocity profile of the induced air can be modeled as a Gaussian distribution. The radius of the particle plume is found to increase linearly with increasing drop height, and it also increases with increasing bulk solid mass flow rate. Comparisons are made with other entrainment flows, such as jets and plumes, and it was found that air entrainment and hence the angle of spread of the particle-driven plumes was much less than for the other entrainment flows. The angles of spread of the particle-driven plumes were found to be in the range 1.3 degrees < theta(s) < 1.8 degrees as compared to theta(s) approximate to 5.7 degrees for miscible plumes arising from sources of heat, for example. In addition, the centerline velocity of the induced air in the particle plumes was found to increase significantly with increasing drop height. Results from high-speed digital video records show that the bulk material does not dilate in a uniform manner as it falls, and a series of distinct particle clouds form in the core of the particle-driven plume. These clouds eventually disperse over a sufficiently large drop height.