Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E10: Drops: LevitationDrops
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Chair: Vladimir Ajaev, Southern Methodist University Room: 503 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E10.00001: Explosive Leidenfrost droplets Pierre Colinet, Florian Moreau, St\'ephane Dorbolo We show that Leidenfrost droplets made of an aqueous solution of surfactant undergo a violent explosion in a wide range of initial volumes and concentrations. This unexpected behavior turns out to be triggered by the formation of a gel-like shell, followed by a sharp temperature increase. Comparing a simple model of the radial surfactant distribution inside a spherical droplet with experiments allows highlighting the existence of a critical surface concentration for the shell to form. The temperature rise (attributed to boiling point elevation with surface concentration) is a key feature leading to the explosion, instead of the implosion (buckling) scenario reported by other authors. Indeed, under some conditions, this temperature increase is shown to be sufficient to trigger nucleation and growth of vapor bubbles in the highly superheated liquid bulk, stretching the surrounding elastic shell up to its rupture limit. The successive timescales characterizing this explosion sequence are also discussed. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E10.00002: Levitation height for ordered arrays of microdroplets over solid-gas and liquid-gas interfaces Dmitry Zaitsev, Dmitry Kirichenko, Vladimir Ajaev, Oleg Kabov We report novel experimental observations of levitating droplets of liquid condensate which organize themselves into ordered arrays over hot liquid-gas and solid-gas interfaces. Mathematical models are developed that explain the mechanisms of droplet levitation for both configurations and lead to new power laws for the levitation height as a function of droplet size. The predictions of the models are shown to be in good agreement with the experimental data. Using the insights from the models and new experiments, we are able to resolve some long-standing controversies from previous studies of levitating droplets. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E10.00003: Leidenfrost wheels Ambre Bouillant, Timothee Mouterde, Philippe Bourrianne, Christophe Clanet, David Quere The high mobility of Leidenfrost drops is commonly attributed to the lack of contact with the hot substrate, and it makes them sensitive to tiny forces, such as gravity or airflows. However, we observed that drops deposited without initial velocity on strictly horizontal substrates self-propel in random directions. This phenomenon~is triggered by confinement. PIV measurements reveal that, as the drop aspect ratio of the drop becomes of order unity, internal motions of liquid systematically switch from toroidal axisymmetric to~asymmetric~rolling. Such a flow reshapes the vapor thickness and tilts it, as evidenced by interferometric measurement, hence leading to propulsion. Droplets are thus found to generate their own dynamics and self-propel despite the absence of external field, which contributes to their legendary mobility [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E10.00004: Inverse Leidenfrost effect: self-propelling drops on a bath Anais Gauthier, Devaraj van der Meer, Detlef Lohse When deposited on very hot solid, volatile drops can levitate over a cushion of vapor, in the so-called Leidenfrost state. This phenomenon can also be observed on a hot bath and similarly to the solid case, drops are very mobile due to the absence of contact with the substrate that sustains them. We discuss here a situation of `` inverse Leidenfrost effect '' where room-temperature drops levitate on a liquid nitrogen pool - the vapor is generated here by the bath sustaining the relatively hot drop. We show that the drop's movement is not random: the liquid goes across the bath in straight lines, a pattern only disrupted by elastic bouncing on the edges. In addition, the drops are initially self-propelled; first at rest, they accelerate for a few seconds and reach velocities of the order of a few cm/s, before slowing down. We investigate experimentally the parameters that affect their successive acceleration and deceleration, such as the size and nature of the drops and we discuss the origin of this pattern. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E10.00005: Film Levitation of Droplet Impact on Heated Nanotube Surfaces Fei Duan, Wei Tong, Lu Qiu Contact boiling of an impacting droplet impacting on a heated surface can be observed when the surface temperature is able to activate the nucleation and growth of vapor bubbles, the phenomena are related to nature and industrial application. The dynamic boiling patterns us is investigated when a single falling water droplet impacts on a heated titanium (Ti) surface covered with titanium oxide (TiO2) nanotubes. In the experiments, the droplets were generated from a flat-tipped needle connected to a syringe mounted on a syringe pump. The droplet diameter and velocity before impacting on the heated surface are measured by a high-speed camera with the Weber number is varied from 45 to 220. The dynamic wetting length, spreading diameter, levitation distance, and the associated parameter are measured. Interesting film levitation on titanium (Ti) surface has been revealed. The comparison of the phase diagrams on the nanotube surface and bare Ti surface suggests that the dynamic Leidenfrost point of the surface with the TiO2 nanotubes has been significantly delayed as compared to that on a bare Ti surface. The delay is inferred to result from the increase in the surface wettability and the capillary effect by the nanoscale tube structure. The further relation is discussed. [Preview Abstract] |
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