Puddle jumping: Spontaneous ejection of large liquid droplets from hydrophobic surfaces during drop tower tests

Abstract

Large droplets and puddles jump spontaneously from sufficiently hydrophobic surfaces during routine drop tower tests. The simple low-cost passive mechanism can in turn be used as an experimental device to investigate dynamic droplet phenomena for drops up to 104 times larger than their normal terrestrial counterparts. We provide and/or confirm quick and qualitative design guides for such “drop shooters” as employed in drop tower tests including relationships to predict droplet ejection durations and velocities as functions of drop volume, surface texture, surface contour, wettability pattern, and fluid properties including contact angle. The latter is determined via profile image comparisons with numerical equilibrium interface computations. Water drop volumes of 0.04–400 ml at ejection speeds of −0.007–0.12 m/s are demonstrated herein. A sample application of the drop jump method is made to the classic problem of low-gravity phase change heat transfer for large impinging drops. Many other candidate problems might be identified by the reader.

Electro-drop bouncing in low-gravity

“…with k ≈ 1.3 × 10 −10 F/m. This is also of similar form to the charge found The effect of volume on jump velocity U 0 is not immediately evident in the data despite previous work having establishing this relationship [19]. This likely results from large variance in U 0 due to contact line hysteresis during the drop roll-up.…”

“…The characteristic time scale of the rolling up of the contact line scales as [19], which resembles the contact time, τ ≈ 2.6(ρR The physics of these relatively massive drops (far beyond the 1-g 0 millimetric capillary length scale) at once utterly defy terrestrial expectations about the ways in which liquid 'should' behave, and also are of critical practical importance to space systems design where examples of such large capillary length scale multiphase flows are commonplace.…”

Omni-Gravity Nanophotonic Heating and Leidenfrost-Driven Water Recovery System

“…The Leidenfrost effect has been studied extensively for its relevance to numerous applications, including metal manufacturing, fuel combustion, jet and rocket engine propulsion, spray cooling, nuclear reactor cooling, and others (Itaru and Kunihide, 1978;Avedisian and Koplik, 1987;Bernardin et al, 1997;Rein, 2002;Abramzon and Sazhin, 2005;Tarozzi et al, 2007;Sazhin et al, 2010;Gradeck et al, 2011;Wu and Sirignano, 2011). The progression of a particularly applicable line of research has led to the extreme enhancement of Leidenfrost phenomena in microgravity using superhydrophobic (SH) substrates (Biance et al, 2003;Vakarelski et al, 2012;Orzechowski and Wciślik, 2014;Maquet et al, 2015;Attari et al, 2016;Wollman et al, 2016;Rasheed and Weislogel, 2019a;Rasheed and Weislogel, 2019b;Rasheed, 2019). Though our intended application requires a reduced-gravity environment, our reported research is limited to terrestrial demonstrations.…”

The ejection of large non-oscillating droplets from a hydrophobic wedge in microgravity

“…Several recent investigations 11 , 12 have demonstrated a method for large drop ejection from puddles that jump spontaneously from hydrophobic surfaces during routine 2.1 s drop tower tests—the puddle at 1− g o becomes a drop in 0− g o . Figure 1a–g illustrates such puddle jumping for a 5 mL water puddle on a textured PTFE surface with static contact angle θ = 150°.…”