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Splashing of a Drop Impacting on a Thin Liquid Film
| Content Provider | Semantic Scholar |
|---|---|
| Author | Rajendran, Sharmen Jog, Milind |
| Copyright Year | 2015 |
| Abstract | When a drop impinges on a thin layer of liquid, there are one of three outcomes: a prompt splash, or a delayed splash, or deposition on the liquid film. Prompt splash occurs at the instant of drop impact, whereas delayed splash occurs with the breakup of the liquid film of the crown at or beyond the maximum expansion of the crown. An experimental and analytical investigation on the onset of delayed splash is reported in this paper. Experiments are carried out with varying drop sizes ranging from 3.5 mm to 5.2 mm and altering the impact velocity from 1 m/s to 3 m/s. Four different liquids are used to study the effect of liquid properties on the phenomena of splashing. A high speed digital camera Hi-D cam – II version 3.0 – (NAC Image technology) is used to capture the phenomena of splashing. The threshold of splashing is found to be related to drop size, impact velocity, liquid properties and thin film thickness. Experimental analysis shows the significance of inertial, viscous and capillary forces in determining the splash/no-splash (or deposition) boundary. The effects of liquid properties and flow parameters on demarcating splash/no-splash regimes are discussed in the paper. * Corresponding Author: Milind.Jog@uc.edu Introduction The significance of drop impact and its subsequent splashing was recognized in studies as early as 1876 by Worthington [1]. Since then, various components of this process have been examined in a number of experimental, numerical and analytical studies. Spray impingement is a common tool used in a multitude of industries to enhance heat and mass transfer. Workers and operators in such industries, that involve spray coating, metal annealing and fertilizer sprays, are in constant danger of contact and/or inhalation of these small drops of toxic chemicals. A means to predict and control the splash occurring, while maintaining the functionality of the process, becomes crucial. Due to the inherent complexities in the drop post impact behavior, understanding of the subject in its entirety, is far from complete. With the exception of a few applications, most spray impingement occurs on a thin film accumulated after impact from previous droplets. The interaction of a liquid drop impinging on a layer of thin film is addressed in the present work. When a drop impinges on a thin liquid film, it leads to different regimes of liquid movement that can broadly be classified under deposition or splashing. Illustrations of these regimes are provided in Table 1. Deposition, post impact of a drop, involves the drop merging with the liquid film without forming secondary drops. Deposition may or may not include capillary surface waves that form a crown of liquid, before merging with the liquid film. Splashing happens when secondary drops are formed as the drop impacts the thin film. At high Weber numbers (We) and high Reynolds numbers (Re) , on impact, an ejected jet is formed at the neck (small region between the drop and the thin film). The ejected jet, spreads out and tilts upwards, forming a crown whose rims are unstable and breakup into secondary drops before merging into the thin film. This was termed crown splashing by Deegan et al. [2] and by Josserand and Zaleski [3]. Table 1. Images showing (a) deposition (no splash), (b) prompt splash and (c) crown (delayed) splash along with respective properties. (a) Liquid: 50% by volume Propylene Glycol (b) Liquid: Water (c) Liquid: 50% by volume |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.ilass.org/2/conferencepapers/11_2015.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
