https://scholars.lib.ntu.edu.tw/handle/123456789/598934
標題: | Transitions of bouncing and coalescence in binary droplet collisions | 作者: | Huang K.-L Pan K.-L. KUO-LONG PAN |
關鍵字: | breakup/coalescence;drops;Drop breakup;Binary droplet collisions;Breakup/coalescence;Droplet diameters;Droplets impact;Governing parameters;Length scale;Mechanism-parameters;Ohnesorge number;Scaling analysis;Weber numbers;Coalescence;coalescence;viscosity | 公開日期: | 2021 | 卷: | 928 | 來源出版物: | Journal of Fluid Mechanics | 摘要: | In droplet impacts, transitions between coalescence and bouncing are determined by complex interplays of multiple mechanisms dominating at various length scales. Here we investigate the mechanisms and governing parameters comprehensively by experiments and scaling analyses, providing a unified framework for understanding and predicting the outcomes when using different fluids. Specifically, while bouncing had not been observed in head-on collisions of water drops under atmospheric conditions, it was found in our experiments to appear on increasing the droplet diameter sufficiently. Contrarily, while bouncing was always observed in head-on impacts of alkane drops, we found it to disappear on decreasing the diameter sufficiently. The variations are related to gas draining dynamics in the inter-droplet film and suggest an easier means for controlling bouncing as compared to alternating the ambient pressure usually sought. The scaling analysis further shows that for a given Weber number, enlarging droplet diameter or fluid viscosities, or lowering surface tension contributes to a larger characteristic minimum thickness of the gas film, thus enhancing bouncing. The key dimensionless group is identified, referred to as the two-phase Ohnesorge number, the Ohnesorge number of liquid and the Hamaker constant, respectively. Our thickness-based model indicates that as 21.1 hcr, where is the maximum value of the characteristic minimum film thickness and is the critical thickness, bouncing occurs in both head-on and off-centre collisions. That is, when [3]A, a fully developed bouncing regime occurs, thereby yielding a lower coalescence efficiency. The transitional Weber number is found universally to be 4. ? 2021 The Author(s). Published by Cambridge University Press. |
URI: | https://www.scopus.com/inward/record.uri?eid=2-s2.0-85117228367&doi=10.1017%2fjfm.2021.797&partnerID=40&md5=1bd1caa3f2ca621cd6281dc67b4971ca https://scholars.lib.ntu.edu.tw/handle/123456789/598934 |
ISSN: | 00221120 | DOI: | 10.1017/jfm.2021.797 |
顯示於: | 機械工程學系 |
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