Experimental Correlation for Splashing Condition of Droplets on Solid Substrates

Yukihiro Yonemoto,Minori Yamashita,Tomoaki Kunugi,Kanta Tashiro

doi:10.3390/fluids7010038

Yukihiro Yonemoto, Minori Yamashita + Show 2 more

Open Access

https://doi.org/10.3390/fluids7010038

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Abstract

Droplet splashing behaviors of water-ethanol binary mixture liquids on roughened solid surfaces were experimentally observed in order to investigate the effects of surface tension, viscosity, and wettability/surface roughness on the splashing occurrence. The range of the droplet volumes was from 1.7 μL to 32.6 μL. The ranges of the surface tension and the viscosity were from 21.1 mN/m to 71.9 mN/m, and from 1 mPas to 2.91 mPas, respectively. The surface roughness range was from 0.03 μm to 1.25 μm for Ra. The present experimental data were evaluated on the basis of the existing models. Resulting from these experiments, a simple model using the Ohnesorge number evaluated by the capillary length was proposed and the accuracy of the predicted critical values such as the critical Weber and Reynolds numbers were discussed. The result indicated that the liquid properties and the quantification of the surface condition such as surface roughness are important factors for the prediction of the splashing behavior.

Highlights

Droplet impingement behavior is related to inkjet printing [1], spray cooling [2,3], spray painting [4], fuel injection [5], and pesticide spray in agriculture [6]
As to the deposition process, at the present time, there are many studies for the prediction of the dimensionless maximum spreading diameter called the spreading factor βm (= dmax /d0 : dmax is the maximum spreading diameter, d0 is the initial droplet diameter) from the experimental, numerical, and theoretical [8,9,10,11,12,13,14,15,16,17] point of views, βm includes the definition of both contact area diameter and the diameter between the rim edges in some literature [18]
The prediction of the droplet splashing behavior depends on the empirical approach and is still an open question

Summary

Introduction

In such applications, the precise predictions of the droplet behaviors such as the spreading size of the droplet, the contact time between liquid and solid surface during the impingement process and splashing or not are very important for an estimation of effective heat transfer, efficient consumption of the pesticide, coating material, and the inkjet process. The behavior is mainly classified into three processes such as the deposition, spreading with surface instability such as a finger, and splash with a secondary droplet from the tip of the liquid film [7]. The prediction of the droplet splashing behavior depends on the empirical approach and is still an open question

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