Transcript Drop Impact on Small Targets David Frankel, Cynthia Ericksen, Paulo E.

Drop Impact on Small Targets
David Frankel, Cynthia Ericksen, Paulo E. Arratia
Franklin Towne Charter High School, Dept. of Mechanical Engineering and Applied Mechanics, University of Pennsylvania
Introduction
Drop impact on solid and liquid surfaces is a rich phenomenon of great
practical and scientific interest [1-5]. Drop impact is central to many
processes used in the petroleum industry including spray painting,
spray coating, and spray cooling of surfaces such as turbine blades
and internal combustion engines. Drop impact on surfaces is often
seen in nature and in everyday life as well. Nail-like jets and bubbles
are familiar spectacles when rain falls on puddles and ponds. Harold
Edgerton [6] captured the beauty and complexity of splashes in the
now famous Milkdrop Coronet (Fig. 1)
An interesting way of simplifying the problem is to consider a situation
in which the typical length scale of the target is of the same order of
magnitude as the drop (L≈d) In this situation, the interaction of the
drop with the target substrate is minimized. Many practical
applications involve substrates that have small surfaces including
spray coating/dispensing technology for applying catalyst inks on
small particles and fuel cell membranes . However, to date, only a
limited number of investigations focus on drop impact in which L≈d.
In fact, there is no published work on numerical simulations of a drop
impacting a small target. Experimental results have shown that, at the
edges of the spreading liquid, free rims are formed and can develop
fingering patterns
Fig.1: Edgerton’s
famous
photograph:
Milkdrop Coronet
– 1957 (Palm
Press, Inc.)
Data/Results
Drop impacting a small target at high velocities. Images are taken at
3000 frames per second. (a) Drop is formed using a syringe pump
and allowed to fall in air. (b) Impact moment – note drop deformation.
(c) A spherical drop spreads into two-dimensions a liquid lamella
sheet. (d) Fingering pattern is observed at the edges of the liquid rim.
(e) Small secondary droplets are formed.
Conclusion
The main goal of this research proposal is to obtain a
fundamental understanding of the drop impact process in a
situation where the length scale of the substrate is of the
same order of magnitude as the impacting drop (L≈d).
Both numerical simulations and experiments will be
performed to investigate the effects of surface tension and
viscoelasticity under low and high Reynolds number
conditions. Experiments will be used to both gain insight
into the impact process and to validate the numerical
simulations. Once validated, simulations will be able to
provide further insight into the impact process.
Future Work
These pictures are taken at 30,000 frames per second, and are then analyzed
using IDL to produce the results below.
Research will continue in this area, with a larger and more
direct focus on taking pictures and videos from above the
drop impact site. This will provide more accurate data
and information for further studies.
Methods
Figure 2: Drop impact conditions. (a) Drop impact
in which the surface length scale (L) is much
larger than the drop size (D). (b) This proposed
work: the drop size (D) is of the same order of
magnitude as the target length scale (L)
The drop height is 40 cm and its diameter is 24 cm. Drops will be
dispensed inside the cylindrical vessel using a precision needle and a
low noise syringe pump, which enable a controlled release of
spherical drops. The drop radius is expected change according
to)/(~grρσ, where g is gravity. The impact velocity (U) is varied by
adjusting the fall height and also by changing the surrounding media
(gas versus liquid). The targets will be inserted in the cylindrical
vessel and will be made of either Delrin® or glass. Different target
diameters will be used such that 1.0 mm<L<5.0 mm.
Qualitative observations of the drop morphology, patterns, and
instabilities will be performed using simple bright lights and a fast
CMOS camera (Photron SA1.1), which will be taking pictures at
30,000 fps and 512x352 pixels. The drop velocity and acceleration
(dU/dt) will be measured using interfacial tracking methods and image
analysis. Measurements will include drop impact and spreading
velocity, drop de-acceleration, and secondary droplet size distribution.
References
P.E. Arratia, J.P. Gollub, and D.J. Durian, "Polymer drop
breakup", Chaos (2007) - Gallery of Nonlinear Images
P.E.Arratia, D. Dragutinovic. Drop Impact on Small Targets:
Exploring Capillary Forces and Viscoelasticity
Bergeron, V.;Bonn, D.;Martin, J.Y.;Vovelle, L. Controlling
drop deposition with polymer additives. Nature 2000, 405,
772-775.
[2] de Gennes, P.G. Wetting: statics and dynamics. Review
of Modern Physics 1985, 57, 827-863.
Acknowledgements
National Science Foundation under Grant No. EEC0743111