Jiao Yunlong, Hu Xidong, Zhu Yongqing, Guo Yuhang, Ji Jiawei, Du Yu, Wang Jiaxiang, Liu Xiaojun, Wang Wei, Liu Kun
Institute of Tribology, Hefei University of Technology, Hefei 230009, China.
Langmuir. 2023 Aug 22;39(33):11925-11933. doi: 10.1021/acs.langmuir.3c01905. Epub 2023 Aug 11.
The impact of droplets on particles involves a wide range of complex phenomena and mechanisms, including bubble nucleation, crater formation, fluidization, and more intricate changes in the boiling regime when impacting superheated particles. In this study, we focus on droplet impact behavior on superheated laminar particles at various temperatures and define six typical characteristic patterns of a single droplet impact on superheated laminar particles, including film evaporation, bubbly boiling, immersion boiling, sputter boiling, transition boiling, and film boiling. It is worth noting that the variations of inertial force caused by gravity, the capillary force generated by the pores of the droplets, and the dewetting force by the vapor phase are the main contributors to different evaporation regimes. Interestingly, we find that the Leidenfrost point (LFP) of droplets on the laminar superheated particles decreases with particle size, which is related to the effect of the pore space generated between the laminar particles. Finally, the effect of temperature, particle size, and Weber number () on the dynamic behavior of droplet impact is revealed. Experimental results show that the instantaneous diameter of droplets is inversely proportional to the change of height, with different patterns of maximum spreading diameter and maximum bounce height at different particle sizes, while the maximum spreading velocity and maximum bounce velocity are independent of particle size. We believe the present work would provide a broader knowledge and comprehension of the droplet impact on heated particles and promote the development of the safety and productivity of industrial processes such as fluid catalytic cracking, spray drying, and spray cooling.
液滴对颗粒的冲击涉及广泛的复杂现象和机制，包括气泡成核、坑洼形成、流化，以及冲击过热颗粒时沸腾状态中更复杂的变化。在本研究中，我们聚焦于不同温度下过热层流颗粒上的液滴冲击行为，并定义了单个液滴冲击过热层流颗粒的六种典型特征模式，包括膜状蒸发、气泡沸腾、沉浸式沸腾、溅射沸腾、过渡沸腾和膜态沸腾。值得注意的是，由重力引起的惯性力变化、由液滴孔隙产生的毛细力以及气相的去湿力是不同蒸发状态的主要影响因素。有趣的是，我们发现层流过热颗粒上液滴的莱顿弗罗斯特温度（LFP）随颗粒尺寸减小，这与层流颗粒之间产生的孔隙空间的影响有关。最后，揭示了温度、颗粒尺寸和韦伯数（）对液滴冲击动态行为的影响。实验结果表明，液滴的瞬时直径与高度变化成反比，不同颗粒尺寸下最大铺展直径和最大反弹高度的模式不同，而最大铺展速度和最大反弹速度与颗粒尺寸无关。我们相信本工作将为液滴对加热颗粒的冲击提供更广泛的认识和理解，并促进诸如流化催化裂化、喷雾干燥和喷雾冷却等工业过程的安全性和生产率的发展。
