Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session A12: Drops: General |
Hide Abstracts |
Chair: Sushant Anand, University of Illinois, Chicago Room: North 126 ABC |
Sunday, November 21, 2021 8:00AM - 8:13AM |
A12.00001: Size distribution of drop diameters in natural rain Maksim Mezhericher, Howard A Stone For more than 100 years scientists have systematically studied diameters of raindrops and discussed which type of distribution function is best able to reflect the physical picture of natural rain. Currently the size distributions of raindrops are fitted to the experimental data using different laws, including Marshall–Palmer's equation, gamma, beta, Weibull, lognormal, exponential, and other distribution functions. Here we show from first principles that in equilibrium the mass and number fractions of raindrop diameters follow lognormal distribution law. From our theory we derived analytical equations describing the probability density function of raindrop diameters and the dependence of mass and count median diameters of raindrops on the rain intensity. Furthermore, we developed a map for the graphical determination of the range of possible diameters and expected median diameter of raindrops at different values of rain intensity. Our results demonstrate good agreement with experimental data obtained by different research groups at various ground locations around the globe for convective and stratiform rains with overall range of rain intensities 0.4-40 mm/h. |
Sunday, November 21, 2021 8:13AM - 8:26AM |
A12.00002: Stability of axisymmetric pendant drops Sravya Sasetty, Thomas Ward This talk focuses on pendant drop experiments conducted to study the stability at Bond numbers, $0.3 < Bo = (L/\lambda_{c})^{2} < 5$, where $R$ is the characteristic length and $\lambda_{c}$ is the capillary length. To determine the characteristic length, we used needle OD for thin-walled needles and ID for thick-walled needles. The fluid drops were generated using a syringe that was mounted on a vertically oriented syringe pump. The syringe pump drove the syringe's plunger at a very low flow rate (1 $\mu$l/min - 50 $\mu$l/min). Images of a pendant drop were captured using a CCD camera. Experiments were performed at room temperature and typically lasted between 5 - 35 min, where evaporation of drops is significant. We used needle diameter of range $0.3$ mm $\leq$ $2R$ $\leq$ $7.9$ mm, and fluids water, ethanol, 5 cSt silicone oil, and glycerol for these experiments. The maximum pendant drop volume just before break-off was measured using an in-house MATLAB code. We plot dimensionless volume ($V^{*} = V/(\pi R)^{3}$) versus Bond number ($Bo$) for the performed experiments. Experiment results were also compared with drop profiles computed at their stability limit using an eigenvalue analysis. The results show good agreement. |
Sunday, November 21, 2021 8:26AM - 8:39AM |
A12.00003: Modeling shear-influenced deformation of drops in a converging channel using lubrication theory Aditya Sangli, David Bigio Fluid flows at low Reynolds number through planar converging channels impose extensional strain on suspended particles along the centerline of the flow. However, when the particles are near the wall, the no-slip condition for the velocity imposes an additional shear component to the total strain. If the suspended particles are deformable -- like drops -- their shape and size can be tuned by simply controlling the flow rate. In this study, we apply concepts from lubrication theory and kinematics of mixing to describe the deformation of drops undergoing shear-influenced deformation. The model considers the initial location of the drop and time spent by it in the flow and generates a space-time phase space that predicts all possible particle trajectories. We show how to calculate the drop deformation from the phase space and experimentally validate the model by tracking the deformation of Silicone oil drops in a flow of Castor oil through a converging channel. Our model accurately predicts the net drop deformation for different combinations of initial drop location and time spent in the flow by the drop. The model can be conveniently used to calculate drop deformation in flows where the single-phase flow solution is available. |
Sunday, November 21, 2021 8:39AM - 8:52AM |
A12.00004: Droplets with Slippery Interfaces David Salac, Afsoun Rahnama Falavarjani Physical systems such as surfactant laden-droplets or those with polymeric interfaces exhibit interfacial slip at the multiphase fluid interface. This slip can dramatically alter the dynamics of these systems in the presence of fluid flow. In this work, the dynamics of such a system are numerically investigated via a novel mixed continuous/discontinuous fluid model, whereby material properties are assumed to smoothly change across the interface while the fluid velocity is discontinuous. After a brief discussion of the numerical methods involved, including the full coupling between the fluid velocity and the velocity slip, the influence of interfacial slip on the resulting dynamics, including droplet breakup, will be explored and compared to available experiments. |
Sunday, November 21, 2021 8:52AM - 9:05AM |
A12.00005: Two-layer viscous drops on inclined surfaces Kasturi Shah, Samuel S Pegler, Brent M Minchew We present a theoretical and experimental study of the dynamics of two-layer viscous drops driven by gravity on inclined surfaces, motivated by natural, biological and industrial phenomena involving the interactions between two fluid layers, e.g. lubrication. A model describing the evolution of two fluids on an inclined substrate is developed and explored to reveal a variety of flow regimes for different modes of release. The asymptotic reduction of this problem due to the dominance of the along-slope component of gravity is shown to yield significant analytical inroads compared to previous studies of multi-layer flow configurations, which have focused exclusively on the case of horizontal beds. For the canonical example in which two fluids are introduced at a constant flux, the flow forms two regions: an upstream region containing both fluids, and a downstream region comprised purely of the lighter fluid, with a sharp intervening jump in thicknesses between the two. By constructing similarity solutions, we establish a full regime diagram of the possible configurations over all asymptotic limits of the viscosity, flux and density ratios. For the release of two fixed volumes of fluid, the layers separate completely into two disjoint but connected drops, contrasting in essential structure from the constant-flux case. Even a small volume of the heavier drop is able to significantly accelerate the propagation of the lighter drop in front of it. Excellent agreement is found between our theoretical predictions and the results of a series of laboratory experiments. |
Sunday, November 21, 2021 9:05AM - 9:18AM Not Participating |
A12.00006: Computational Investigation of Drop Behavior and Breakup in Peristaltic Flow Kathleen Feigl, Franz X Tanner The deformation and breakup behavior of liquid drops in the retropulsive jet produced by a peristaltic wave is investigated computationally. This study is motivated by recent experimental work on drop breakup in antral contraction wave flow in a model stomach. The goal is to expand the insights obtained in these experiments by considering a wider range of conditions, and to classify drop breakup more precisely. The computational geometry consists of a tube that is closed at one end; the peristaltic wave that deforms the tube boundary is modeled as a traveling wave moving toward the closed end. For these simulations, an OpenFOAM solver was developed which combines adaptive mesh refinement around deforming and moving drops with dynamic meshing techniques for domains with deforming boundaries. The new solver is first validated, where good agreement is found with experimental data. A parametric study is then performed where the interfacial tension, viscosity ratio, relative occlusion, and initial drop position are varied. The effects of these parameters on the drop's transit time, deformation, and breakup characteristics are determined. In particular, breakup regimes on graphs of capillary number versus viscosity ratio are found for each initial drop position and relative occlusion. |
Sunday, November 21, 2021 9:18AM - 9:31AM |
A12.00007: Sessile drops in weightlessness: an ideal playground for challenging Young's equation Marc Médale, David Brutin Sessile drop creation in weightlessness is critical for designing scientific instruments for space applications and for manipulating organic or biological liquids, such as whole human blood or DNA drops. It requires perfect control of injection, spreading, and wetting; however, the simple act of creating a drop on a substrate is more complex than it appears. A new macroscopic model is derived to better understand this related behaviour. We find that, for a given set of substrate, liquid, and surrounding gas properties, when the ratio of surface free energies to contact line free energy is on the macroscopic scale, the macroscopic contact angle can vary at static equilibrium over a broad volume range. It can increase or decrease against volume depending on the sign of this ratio up to an asymptotic value. Consequently, our model aims to explore configurations that challenge the faithful representativity of the classical Young's equation and extends the present understanding of wetting |
Sunday, November 21, 2021 9:31AM - 9:44AM |
A12.00008: Shape-tunable synthesis of alginate particles Sima Asadi, Arif Z. Nelson, Patrick Doyle Alginate microparticles are extensively used in pharmaceutical, cosmetic, and food industries due to their biocompatibility, biodegradability, and non-toxicity. Non-spherical alginate particles offer several advantageous features important to controlled drug release and cell encapsulation, including higher surface to volume ratio and a shorter diffusion path. Here, we synthesize shape-tunable alginate particles by dripping a sodium alginate solution with various concentrations of a yield-stress fluid, such as Carbopol, into an aqueous CaCl2 bath where the droplet is subsequently ionically crosslinked. We take advantage of the yield stress property of Carbopol to tune the shape of the resulting particles. We identify several distinct regimes of alginate particle formation, ranging from symmetrical, spherical beads to asymmetric, anisotropic morphologies. Our results suggest that droplet deformation is initially (before bath entry) determined by the relative strength of yield-stress and surface forces. After the bath entry, a competition between the time scales of the yield-stress fluid relaxation and the crosslinking reaction determines the overall shape |
Sunday, November 21, 2021 9:44AM - 9:57AM |
A12.00009: Statistics of drops generated from ensembles of randomly corrugated ligaments Sagar Pal, Stephane L Zaleski, Marco Crialesi-Esposito, Daniel Fuster The size of drops generated by the capillary-driven disintegration of liquid ligaments plays a fundamental role in several important natural and industrial phenomena. The inherent non-linearities of the equations governing ligament destabilization lead to significant differences in the resulting drop sizes, owing to small fluctuations in the myriad initial conditions. Previous experiments and simulations reveal a variety of drop size distributions, corresponding to competing underlying physical interpretations. Here, we perform numerical simulations of individual ligaments, the deterministic breakup of which is triggered by random initial surface corrugations. Stochasticity is incorporated by simulating a large ensemble of such ligaments, each realization corresponding to a random but unique initial configuration. The resulting probability distributions reveal three stable drop sizes, generated via a sequence of two distinct breakup stages. The probability of the large sizes is described by volume-weighted Poisson and Log-Normal distributions for the first and second breakup stages, respectively. The study demonstrates a quantitatively precise, statistically robust and reproducible framework for studying drop sizes resulting from complex liquid fragmentation phenomena. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700