Low Speed Drop Impact Onto Dry Solid Surfaces
The orthogonal impact of a Newtonian liquid drop impact onto dry solid surfaces is studied. The focus was placed on finding the possible outcomes of the drop impact and the time evolution of the impact process. A new phenomenological classification differ
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Institute for Fluid Mechanics and Aerodynamics, Technical University of Darmstadt, Germany
Abstract. The orthogonal impact of a Newtonian liquid drop impact onto dry solid surfaces is studied. The focus was placed on finding the possible outcomes of the drop impact and the time evolution of the impact process. A new phenomenological classification differentiates between six possible outcomes. In order to be able to identify the influencing parameters, changes of drop diameter, impact velocity, surface tension, viscosity, advancing and receding contact angles, roughness amplitude and wavelength have been made. The influences of these impact parameters on the various phases of the impact process has been investigated.
1 Introduction and Description of Experiment Despite a large body of Iiterature on the subject of drop impact onto solid surfaces dating back well over a century, it became apparent in preliminary studies that several possible outcomes observed for certain parameter variations had not yet been documented or classified. The present experimental study therefore, aimed to cover a large range of impact parameters and to identify the possible outcome seenarios of the impact. A first attempt to establish parameter ranges within which each outcome occurs has also been made. Single drops were generated by a precision syringe and allowed to drop onto a prepared target from various heights. A light barrier placed above the target and an electronic delay were used to trigger a high resolution CCD camera (PCO Sensicam), which could take single or multiple exposures (up to 10 images) of the drop impact. Back lighting was used for illumination.
Table 1: Range of parameters: V; Impact velocity; D Drop diameter; vviscosity; uSurface tension; RA & Rw Roughness amplitude & wavelength; Bat~v. & Brec. advancing & receding static contact angles
Min. Max. Min. Max.
Vi (m!s)
D(mm)
v(cS)
u(N/m)
0.7 4.2
1.8
1 1000
0.02 0.073
RA (f,-lm)
Rw(f.-lm) 100 1000
0.003 120
5
Badv.
CO)
0 160
l+ec. CO) 0 135
• We thank the Deutsch Forschungsgemeinshaft for financial support through grant Tr 192/12. M. Rein (ed.), Drop-Surface Interactions © Springer-Verlag Wien 2002
R. Rioboo and C. Tropea
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Both the target material and the liquid were varied allowing the parameter range shown in the Table 1 to be achieved. In the present study, the main results consisted of the recorded images and their classification according to outcome. Quantitative data conceming e.g. the speed of spreading or maximan spreading diameter was extracted from a serie of images.
2 Results Figure 1 summarizes the possible outcomes which have been observed. The two extreme cases are complete deposition or complete rebound, in which the drop experiences no break-up. Breakup occurs however in the other four possible outcomes: prompt splash, corona splash, receding break-up and partial rebound. Deposition
Prompt pla. h orona plash
. ...
-~
-
................, ....
:•.~
Recediog break·up
Partial rebound
Rebound
Figure 1: Outcomes from a drop
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