Abstract
The rim breakup of an impacting drop is experimentally investigated by comparing the impacts on superheated and superhydrophobic surfaces. The objective of the present study is to experimentally examine whether the Bo = 1 criteria holds for the rim breakups of drops impacting on the surfaces. A transparent sapphire plate was heated to achieve the Leidenfrost impact, which enables us to observe with a high-speed camera from below. The characteristics of the rim breakup were evaluated quantitatively using a particle tracking velocimetry method for both the rim and the drops generated. As a result, we clarified that Bo of the rim increases in the spreading phase and marks the highest value of 0.5 on a superheated surface, which is smaller than that on a pillar, where Bo ≈ 1. On a superhydrophobic surface, the highest Bo was 1.2, which is smaller than that on a wettable solid surface, 2.5, but close to the value on a pillar. We also revealed that diameters of generated drops collapse on a master curve when plotted as a function of pinch-off time for both the impacts on superheated and superhydrophobic surfaces.
Highlights
Drop impact is an important fundamental process that determines the quality and the efficiency in many industrial applications including painting, coating, engine combustion, and spray cooling
The objective of the present study is to experimentally examine whether or not the Bo = 1 criteria holds for the rim breakups of drops impacting on a superhydrophobic surface and a superheated one above the Leidenfrost temperature
The rim shrunk on the SHPB surface due to the surface tension of the film surrounded by the rim, while on the SH surface, both the rim and film disintegrated into small pieces
Summary
Drop impact is an important fundamental process that determines the quality and the efficiency in many industrial applications including painting, coating, engine combustion, and spray cooling. The physics of drop impact have been widely investigated. The maximum spreading diameter has been studied in detail. Many theoretical models on the maximum spreading have been derived based on the conservation of energy for the impact of a pancake-shaped drop [1,2,3,4,5,6,7,8,9]. More realistic models for the shape of the impacting drop were derived [10]. Expanding and contracting dynamics of the rim are a target in the study of drop impact [5,10,11,12]
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