Atomization and Sprays Journal of the International Institutes for Liquid Atomization and Spray Systems

ISSN for PRINT: 1045-5110

For Online Access

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2005, Volume15

Issue 1

122 pages

DOI: 10.1615/AtomizSpr.v15.i1

Issue price - $92.00

S. Nigen
Department of Mathematics, University of Wales Aberystwyth, Ceredigion, UK

This experimental study concerns the impact of droplets of yield-stress materials onto flat surfaces. A commercial vaseline was selected to undertake the study. This fluid exhibits a measurable yield stress and permits the development of a droplet. Its basic characteristics (density, static surface tension) were determined and its rheology characterized. The viscosity data have been modeled using a Cross model, modified to build in a yield stress.
Droplets of the fluid were impacted upon a dry, smooth Plexiglas surface. Their deformations after impact were visualized using a high-speed video camera operating at acquisition rates of 9000 or 13,500 frames a second.
For low-impact velocities, the droplets first behave like deformable solids. Then a long-time-scale creeping flow takes place. For high-impact velocities, each droplet is seen to start spreading onto the surface. As it spreads, its velocity decreases and the stresses decrease until they eventually fall below their yield value. When the limit is reached, the spreading stops suddenly. Then, surface tension is not strong enough to overcome the yield stress and the recoil of the droplet is prevented.
Consequently, the final shape of the droplet depends on when the yield-stress limit is reached in the spreading phase. When increasing the impact velocity, the maximum spreading increases and the flow stops sooner.

DOI: 10.1615/AtomizSpr.v15.i1.60 Download article, 103-118 pages

Article price - $35.00

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