Grazing impact of continuous droplet streams with a superhydrophobic surface

• Published in: Experiments in fluids Vol. 49; no. 5; pp. 1109 - 1119
• Main Authors: Chiarot, Paul R., Jones, T. B.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.11.2010; Springer
• Subjects: Circulation; Condensed matter: structure, mechanical and thermal properties; Correlation; Droplets; Drops and bubbles; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Exact sciences and technology; Fluid dynamics; Fluid- and Aerodynamics; Fundamental areas of phenomenology (including applications); Grazing; Heat and Mass Transfer; Instrumentation for fluid dynamics; Kinetic energy; Nonhomogeneous flows; Oscillations; Physics; Research Article; Solid-fluid interfaces; Streams; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Weber number; Wetting; Energy Audit; Individual Droplet; Droplet Impact; Superhydrophobic Surface; Heating Pulse; Test facilities; CCD camera; Wetting; Stroboscopy; Grazing incidence; Impact phenomena; Droplets; Hydrophobicity; Experimental study
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-010-0860-x

When high-velocity droplets make grazing impact with a superhydrophobic surface, the droplets undergo significant deformation before recoiling and rebounding from the surface. Two distinct operating regimes describe the response of the reflected droplet stream after impact. In the first regime, the droplets remain discrete and uniform after the impact, but exhibit rotation and significant oscillations. This regime dominates if each droplet can clear the impact region before the next droplet arrives. In the second regime, droplets cannot avoid coalescing into a puddle at the surface. A secondary jet is ejected from the puddle which breaks up into a random droplet stream after traveling a short distance due to the lack of a forced unstable perturbation. The droplet-to-droplet spacing in the incoming stream determines which regime rules, with the critical value correlated by a Weber number. In the first regime, a detailed accounting of the kinetic and potential energies reveals that neither droplet oscillation nor rotation can fully account for the loss of translational kinetic energy, indicating significant internal circulation must occur in the droplets at impact. An application of droplet rebound from a superhydrophobic surface is proposed.