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Impact of droplets on immiscible liquid films†
Soft Matter ( IF 2.9 ) Pub Date : 2018-01-02 00:00:00 , DOI: 10.1039/c7sm02089a
Zhizhao Che 1, 2, 3, 4, 5 , Omar K. Matar 5, 6, 7, 8
Affiliation  

The impact of droplets on liquid films is a ubiquitous phenomenon not only in nature but also in many industrial applications. Compared to the widely-studied impact of droplets on films of identical fluids, the impact of droplets on immiscible films has received far less attention. In the present work, we show using high-speed imaging that immiscibility has a profound effect on the impact dynamics. The impact of a water droplet on an oil film leads to the formation of a compound crown followed by a central jet, whereas that of an oil droplet on a water film results in rapid spreading on the film surface driven by a large, positive spreading factor. In the former scenario, the central jet occurs due to the severe stretching of the droplet during the formation of the crown and then the retraction of the droplet by capillarity, which leads to the collision of fluid at the impact point. A model for the elongation dynamics of the central jet is proposed based on energy conservation. The effects of key parameters controlling the impact process are analysed, including the droplet Ohnesorge and Weber numbers, the viscosity ratio, and the dimensionless film thickness. Different impact outcomes are discussed, such as bouncing, deposition, and oscillation of the impact droplet, the formation and collapse of the compound crown, and the formation and tip-pinching of the central jet. This study not only provides physical insights into the impact dynamics, but could also facilitate the control and optimisation of the droplet impact process in a number of applications as highlighted herein.

中文翻译:

液滴对不溶混液体薄膜的影响

液滴对液膜的影响不仅在自然界而且在许多工业应用中都是普遍存在的现象。与广泛研究的液滴对相同流体的薄膜的影响相比,液滴对不混溶的薄膜的影响受到的关注要少得多。在当前的工作中,我们展示了使用高速成像技术,不相溶性对撞击动力学具有深远的影响。水滴在油膜上的冲击导致形成复合冠,随后形成中心射流,而水滴在油膜上的冲击导致在膜表面上迅速扩散,这是由较大的正扩散因子驱动的。在前一种情况下,由于在冠形成过程中液滴的严重拉伸,然后由于毛细作用而使液滴回缩,因此产生了中心射流,导致流体在撞击点发生碰撞。提出了基于能量守恒的射流伸长动力学模型。分析了控制冲击过程的关键参数的影响,包括液滴的Ohnesorge和Weber数,粘度比和无因次膜厚度。讨论了不同的冲击结果,例如冲击液滴的弹跳,沉积和振荡,复合物冠的形成和塌陷以及中央射流的形成和尖端收缩。这项研究不仅提供了对撞击动力学的物理见解,而且还可以在本文重点介绍的许多应用中促进液滴撞击过程的控制和优化。提出了基于能量守恒的射流伸长动力学模型。分析了控制冲击过程的关键参数的影响,包括液滴的Ohnesorge和Weber数,粘度比和无因次膜厚度。讨论了不同的冲击结果,例如冲击液滴的弹跳,沉积和振荡,复合物冠的形成和塌陷以及中央射流的形成和尖端收缩。这项研究不仅提供了对撞击动力学的物理见解,而且还可以在本文重点介绍的许多应用中促进液滴撞击过程的控制和优化。提出了基于能量守恒的射流伸长动力学模型。分析了控制冲击过程的关键参数的影响,包括液滴的Ohnesorge和Weber数,粘度比和无因次膜厚度。讨论了不同的冲击结果,例如冲击液滴的弹跳,沉积和振荡,复合物冠的形成和塌陷以及中央射流的形成和尖端收缩。这项研究不仅提供了对撞击动力学的物理见解,而且还可以在本文重点介绍的许多应用中促进液滴撞击过程的控制和优化。包括液滴的Ohnesorge和Weber数,粘度比和无因次膜厚度。讨论了不同的冲击结果,例如冲击液滴的弹跳,沉积和振荡,复合物冠的形成和塌陷以及中央射流的形成和尖端收缩。这项研究不仅提供了对撞击动力学的物理见解,而且还可以在本文强调的许多应用中促进液滴撞击过程的控制和优化。包括液滴的Ohnesorge和Weber数,粘度比和无因次膜厚度。讨论了不同的冲击结果,例如冲击液滴的弹跳,沉积和振荡,复合物冠的形成和塌陷以及中央射流的形成和尖端收缩。这项研究不仅提供了对撞击动力学的物理见解,而且还可以在本文重点介绍的许多应用中促进液滴撞击过程的控制和优化。
更新日期:2018-01-02
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