Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C24: Drops IILive
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Sponsoring Units: DFD Chair: Vivek Narsimhan, Purdue University Vishal Anand, Purdue Unviersity |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C24.00001: Hydrodynamic Spin Lattices Pedro Saenz, Giuseppe Pucci, Sam E Turton, Alexis Goujon, Rodolfo R Rosales, Jorn Dunkel, John W M Bush We introduce a hydrodynamic analog system that allows us to investigate simultaneously the wave-mediated self-propulsion and interactions of effective spin degrees of freedom in inertial and rotating frames. Millimetric liquid droplets can walk across the surface of a vibrating fluid bath, self-propelled through a resonant interaction with their own guiding wave fields. A walking droplet, or `walker’, may be trapped by a submerged circular well at the bottom of the fluid bath, leading to a clockwise or counter-clockwise angular motion centered at the well. When a collection of such wells is arranged in a 1D or 2D lattice geometry, a thin fluid layer between wells enables wave-mediated interactions between neighboring walkers. For sufficiently strong pair-coupling, wave interactions between neighboring droplets may induce local spin flips leading to the spontaneous emergence of ferromagnetic or antiferromagnetic order. Transitions between these two forms of order can be controlled by tuning the lattice parameters or by imposing a Coriolis force mimicking an external magnetic field. Theoretical predictions based on a generalized Kuramoto model derived from first principles rationalize our experimental observations. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C24.00002: Droplet Dynamics on a Vibrating Vertical Wire Alireza Hooshanginejad, Karl Nicholas Frohlich, Sunghwan Jung Droplet dynamics along a wire is of great fundamental importance in fluid mechanics. From the practical standpoint, using wire mesh to collect droplets or dust particles is a common method in air filtration systems. In this study, we investigate dynamics of a droplet under the effect of vibrations on a vertical wire both experimentally and theoretically. We observe three different behaviors of the drops in experiments: static, sliding, or shedding. We characterize the phase diagram of these distinct behaviors for varying droplet sizes and vibration accelerations. In general, by increasing the vibration acceleration or the drop volume, the drop transitions from static to sliding to shedding. Notably, the sliding velocity in the sliding regime shows a non-monotonic trend as a function of the vibration amplitude under certain frequencies. Finally, we develop a reduced model to rationalize the drop dynamics in the sliding regime. We also develop simple scaling laws to characterize the threshold of shedding behavior. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C24.00003: Capillary flow mediated dynamics of liquid droplet generation from a yarn Bhaskarjyoti Sarma, Amaresh Dalal, Dipankar Narayan Basu The spontaneous capillary imbibition of liquids through the porous netwrok of a yarn is a well studied phenomena and finds its application in numerous industrial processes. Of late, threads/yarns have been used as microfluidic devices, under the name μ-TAD, to study biochemical reactions, mixing of reagents, or as smart bandages. Interestingly, we find that, such an spontaneous flow can also result in the formation of liquid droplets at the freely hanging end of a verticaly placed yarn. However, the dynamics of the liquid droplet formation from a yarn is substantially different than that of a solid non-wettable nozzle. In the former the droplet growth is observed in three distinct modes namely, "radial growth", "axial growth", and "motion" regime. Each of the aforementioned stages exhibit distinct contact line and interfacial dynamics as the droplet grow freely in the yarn. We explore with a range of liquid viscosity to show that these dynamics in each regime are universal and can be elucidated with the help of unified scaling laws. Further, critical droplet volumes for the "motion" stage can also be derived theoretically, which in turn determines the pinch-off liquid volume. Such an system can be exploited as a prototype for the development of porous, wettable nozzles in future. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C24.00004: Atomization regimes in liquid jets due to pressure driven flow in a cylindrical nozzle with MHz frequency acoustic vibration William Connacher, Jeremy Orosco, James R Friend In acoustofluidic atomization, high-frequency oscillation accelerates and destabilizes liquid in contact with a vibrating piezoelectric substrate. This method has an advantage over alternatives that rely on nozzles and high pressure-driven flow. However, these methods may be combined to produce atomization superior to either alone. Nozzles may be machined directly in piezoelectric media, producing predictable Rayleigh jetting at moderate pressure-driven flow rates in the absence of acoustic excitation. Upon application of MHz-order acoustic vibration above a threshold amplitude, however, Taylor-mode-like atomization results in monodisperse, micron-scale droplets. High-speed microvideography indicates that it occurs directly from the nozzle without spreading onto the adjacent substrate. Acoustic streaming is not a factor. Instead, we suggest that the acoustic oscillation induces characteristic structure within the nozzle. We model this flow and perform stability analysis to reveal the effects of system parameters on capillary wave growth. We predict the atomization threshold and the resulting droplet sizes. We then compare these predictions with experiments for a wide range of fluids, flow rates, and acoustic amplitudes and frequencies. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C24.00005: Joint effect of advection, diffusion, and capillary attraction on the spatial structure of particle depositions from evaporating droplets Konstantin Kolegov, Lev Barash A simplified model is developed, which allows us to perform computer simulations of the particles transport in an evaporating droplet with a contact line pinned to a hydrophilic substrate. The model accounts for advection in the droplet, diffusion and particle attraction by capillary forces. The parameters chosen correspond to the experiments of Park and Moon [Langmuir 22, 3506 (2006)], where an annular deposition and snakelike chains of colloid particles have been identified. We find that the annular sediment is formed by advection and diffusion transport. The close packing of the particles in the sediment is possible if the evaporation time exceeds the characteristic time of diffusion-based ordering. The chains are formed by the end of the evaporation process due to capillary attraction of particles in the region bounded by a fixing radius, where the local droplet height is comparable to the particle size. At the beginning of the evaporation, the annular deposition is shown to expand faster than the fixing radius moves. However, by the end of the process, the fixing radius rapidly outreaches the expanding inner front of the ring. The snakelike chains are formed at this final stage. |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C24.00006: How sedimenting droplets grow and stir the fluid Dhrubaditya MITRA, Akshay Bhatnagar, Prasad Perlekar We study sedimenting droplets in binary fluid mixture in the droplet-spinodal regime using direct numerical simulations of the Cahn-Hilliard-Navier-Stokes equation (model H without noise). In zero-gravity, the characteristic length scale follows t1/3 law where t is time. But, we are neither in the regime of Lifshitz-Sloyzov- Wagner scaling nor in the Binder-Stauffer-Siggia scaling. In non-zero gravity, the scaling crosses over to a t2/3 scaling at late times. During the same late times, the sedimenting droplets stir the fluid consequently the kinetic energy of the fluid grows as t5/3 . Both in absence and presence of gravity the energy spectra of the fluid shows a k-4 scaling at intermediate range of scales although in the former case the energy decays in time and in the latter case it grows with time. We construct a scaling theory that help us understand these numerical results. |
Monday, March 15, 2021 4:12PM - 4:24PM Live |
C24.00007: Chiral Emulsions Laura Adams A robust route for the biased production of single-handed chiral structures has been found in generating non-spherical,multi-component double emulsions using microfluidics. The specific type of handedness is determined by the final packing geometry of four different inner drops inside an ultra-thin sheath of oil. Before three-dimensional chiral structures are formed, the quasi-one-dimensional chain re-arranges in two dimensions into either checkerboard or stripe patterns. We derive an analytical model predicting which pattern is more likely and assembles in the least amount of time. Moreover, our model accurately predicts our experimental results and is based on local bending dynamics, rather than global surface energy minimization. This better reflects the underlying self-assembly process which will not, in general, reach a global energy minimum. In summary, using glass microfluidic techniques for channeling aqueous fluids through narrow orifices of multi-bore injection capillaries while encapsulating these fluids as drops inside an ultra-thin sheath of oil is sufficient to produce single-handed chiral structures. |
Monday, March 15, 2021 4:24PM - 4:36PM Live |
C24.00008: How a raindrop gets shattered on biological surfaces Seungho Kim, Zixuan Wu, Ehsan Esmaili, Jason Dombroskie, Sunghwan Jung Many biological surfaces (e.g. bird feathers, insect wings, and plant leaves) are super-hydrophobic with physical morphology at different scales. However, it is not well understood how a raindrop impacts natural super-hydrophobic surfaces, and its significance of biological functions. In this present study, we found that a spreading drop at a high speed can generate wrinkled pattern (including shock-like waves) on a spreading liquid in the presence of surface morphology at the micro scale. Furthermore, the spreading drop is suddenly ruptured by growing holes followed by the shock waves, which leads to a decrease in contact time more than 50%. As a result, heat and momentum transfers are reduced by raindrops, which may lower the hypothermia risk of animals or less affect the stability of insect flights. Additionally, we revealed that the drop fragmentation sheds smaller satellite droplets, which play a crucial role in promoting wet pathogenic dispersal by carrying pathogenic spores along. Therefore, our results shed light on multi-functional aspects of biological super-hydrophobic surfaces. |
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