Article contents
Self-propelled jumping upon drop coalescence on Leidenfrost surfaces
Published online by Cambridge University Press: 02 July 2014
Abstract
Self-propelled jumping upon drop coalescence has been observed on a variety of textured superhydrophobic surfaces, where the jumping motion follows the capillary–inertial velocity scaling as long as the drop radius is above a threshold. In this paper, we report an experimental study of the self-propelled jumping on a Leidenfrost surface, where the heated substrate gives rise to a vapour layer on which liquid drops float. For the coalescence of identical water drops, we have tested initial drop radii ranging from 20 to $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}500\ \mu \mathrm{m}$, where the lower bound is related to the spontaneous takeoff of individual drops and the upper bound to gravitational effects. Regardless of the approaching velocity prior to coalescence, the measured jumping velocity is around 0.2 when scaled by the capillary–inertial velocity. This constant non-dimensional velocity holds for the experimentally accessible range of drop radii, and we have found no cutoff radius for the scaling, in contrast to prior experiments on textured superhydrophobic surfaces. The Leidenfrost experiments quantitatively agree with our numerical simulations of drop coalescence on a flat surface with a contact angle of 180°, suggesting that the cutoff is likely to be due to drop–surface interactions unique to the textured superhydrophobic surfaces.
- Type
- Papers
- Information
- Copyright
- © 2014 Cambridge University Press
Footnotes
Present address: Laboratoire de Physique de la Matière Condensée, CNRS UMR 7336, Université de Nice Sophia-Antipolis, Parc Valrose, 06108 Nice CEDEX 2, France.
References
Liu et al. supplementary movie
Coalescence on a Leidenfrost surface (figure3a): r=22um, duration=10ms.
Liu et al. supplementary movie
Coalescence on a Leidenfrost surface (figure 4): r=380um, duration=13.3ms.
Liu et al. supplementary movie
Simulated coalescence on a non-wetting surface (figure 6): r=380um, duration=6.6ms.
Liu et al. supplementary movie
Simulated coalescence on a non-wetting surface (figure 6): r=380um, duration=6.6ms.
- 76
- Cited by