Abstract:

Aiming at the granulation of molten blast furnace slag by spinning disc, the visualization granulation experiment was conducted using water as the substance. The granulation process including film waving and ligament break-up was captured by high-speed camera. A self-compiled MATLAB program was employed to extract the data from the images. The ligament formation and the process of ligament break-up into droplets during centrifugal granulation were analyzed. Variation of ligament formation and droplet formation with operating conditions was investigated. The qualitative relationship between ligament formation and droplet formation was obtained. The impacts of Weber and Reynolds numbers on ligament number, ligament break-up length, droplets diameter distribution and average diameter were discussed. The results revealed that the ligaments were originated from surface instable waves of liquid film on the spinning disc and the droplets were formed by ligament break-up due to symmetric shocking waves spreading from the ends to the middle of ligament. The number of ligament increased with increasing rotary speed and the distribution of droplets became more highly concentrated as well, while the break-up length of ligaments and the average diameter of droplets were decreased as rotary speed increased. With increasing liquid flow rate, the number of ligaments increased, while the distribution of droplets became less concentrated. The break-up length of ligaments and average diameter were increased with higher liquid flow rate. Besides, larger ligament number or shorter ligament break-up length resulted in smaller droplets. Meanwhile, both of the Weber and Reynolds numbers had significant influence on the ligament formation, while only the Weber number had significant effect on droplet formation. By fitting the experimental data, correlations have been obtained to predict the granulation variation with different operational conditions quantitatively.

Key words: granulation, multiphase flow, instability, liquid film, droplets, size distribution

摘要：

针对转盘离心粒化工艺,以水为工质开展可视化实验。采用高速摄影仪对液膜波动、液丝断裂等粒化过程进行了捕捉,并利用MATLAB自编程序对获得的图像进行了处理。分析了离心粒化过程中液丝形成过程以及液丝断裂形成液滴的过程。研究了运行工况对液丝、液滴形成机制的影响。讨论了液丝形成对液滴形成的影响并获得了Weber数、Reynolds数对粒化效果的影响程度。结果表明,表面不稳定波是形成液丝的主要因素,且液丝在Rayleigh不稳定性的作用下断裂形成液滴。升高转速或者减小流量有利于获得均匀的小液滴。Weber数对液丝、液滴形成具有显著影响;Reynolds数仅对液丝数目有显著影响。

关键词: 造粒, 多相流, 不稳定性, 液丝, 液滴, 粒度分布