Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session Z02: Drops: Particle Laden (12:15pm - 1:00pm CST)Interactive On Demand
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Z02.00001: Particle agglomeration through Marangoni Bursting Carola Seyfert, Bryan Verveld, Alvaro Marin Marangoni Bursting occurs when a two-component drop, containing water and alcohol, is deposited on an oil bath (Keiser et al. PRL 118.7 (2017): 074504). The two miscible components water and alcohol have different volatilities and surface tensions, leading to a Marangoni flow from the drop center outwards. The thickened rim of the drop becomes unstable and ejects a myriad of tiny droplets, which evaporate further on top of the oil bath. The alcohol concentration in the initial water-alcohol mixture tunes the droplet size distribution of the bursting, with higher alcohol concentrations leading to smaller droplets. In this work, we add colloidal particles in diluted concentrations to the mother drop. Following the Marangoni Bursting, the tiny droplets dissolve and evaporate, turning into small particle clusters, which sit on top of the oil bath. We elaborate on the influence of parameters like alcohol and particle concentration, as well as particle size, on the final particle clusters. [Preview Abstract] |
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Z02.00002: The effect of spatial variation in the evaporative flux on the deposition from an evaporating droplet Hannah-May D'Ambrosio, Stephen K Wilson, Brian R Duffy, Alexander W Wray The evaporation of sessile droplets occurs in numerous physical contexts, including in nature, industry and biology. Of key interest in many scientific and industrial processes is the deposit that is left behind after evaporation. For applications such as inkjet printing, control over the spatial distribution of solute at the end of the drying process is extremely important, with a particular need to obtain uniform deposits. In recent years there has been an explosion of research into the deposition from an evaporating droplet, particularly regarding the ring-like deposit (the ``coffee-ring'') which often forms at the contact line. We investigate the effect of spatial variation of the evaporative flux on the deposition from an evaporating droplet. We consider a one-parameter family of evaporative fluxes, which includes both diffusion-limited and uniform evaporation, as well as fluxes with a maximum at the centre of the droplet, as special cases. We determine the flow velocity, the concentration of solute inside the droplet and the evolution of the deposit. We show that the deposit depends strongly on the evaporative flux profile, observing ring deposits, paraboloidal deposits and deposits near the centre of the droplet, and examine several interesting cases in detail. [Preview Abstract] |
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Z02.00003: COVID-19 Transmission Dynamics: Trajectories of Virus-Laden Droplet Population Flow Model of Coughing and Sneezing Yasser Aboelkassem, Haithem Taha Transmission of severe acute respiratory syndrome coronavirus (COVID-19) is mainly through virus-laden multiscale population of droplets and aerosols. These expiratory fluid particles can spread between infectious and susceptible individuals during coughing and sneezing, causing deadly respiratory illness. Healthcare authorities are searching for effective metric guidelines to minimally prevent community transmission of this virus. In this study, a mathematical model is developed to study the trajectories of fluid particles induced by a puff (momentum driven flow) of coughing/sneezing in a quiescent environment. Initially, the fluid particles are sampled from a population source of various sizes and velocities. The effects of gravitational, buoyancy, drag and deformation forces on the particles trajectories are considered. The results are validated using a mesh-free Lagrangian numerical technique, namely the smoothed-particle hydrodynamics (SPH) method. [Preview Abstract] |
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Z02.00004: Gravity-induced encapsulation of an armored droplet Alireza Hooshanginejad, Ellen Longmire, Sungyon Lee Droplets coated with a protective armor of particles are relevant in stabilization of emulsions and foams that are widely used in many industrial applications, such as pharmaceutical, food, and cosmetics. These armored droplets can form by rolling droplets on a bed of hydrophobic particles [1] or by destabilizing a granular raft of negatively buoyant particles on a fluid interface [2]. In a series of experiments, we investigate an armored droplet of water-isopropanol mixture settling through oil and approaching an oil-water interface. The armored droplet is observed to undergo either rupture or encapsulation, as we systematically vary key physical parameters, such as particle size, particle density, oil viscosity and interfacial tension. In this talk, we discuss the physical mechanism that leads to the two distinct behaviors and identify the key dimensionless parameters that characterize the transition between the two regimes. [1] P. Aussillous and D. Quere, Nature, 2001, 411, 924--927. [2] M. Abkarian, S. Protiere, J.~Aristoff, and H. Stone, Nature Communications, 2013, 4, 1895. [Preview Abstract] |
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Z02.00005: A mathematical model for multi-modality in droplet dispersion Cathal Cummins, Olayinka Ajayi, Felicity Mehendale, Roman Gabl, Ignazio Maria Viola We present a mathematical model for the dispersion of spherical droplets in the presence of a source-sink pair flow field [\underline {Cummins et al. (2020), Phys. Fluids 32 (8)}]. The dynamics of the droplets is governed by the Maxey--Riley equation with the Basset--Boussinesq term neglected. In the absence of gravity, our model predicts two distinct behaviors for the droplets: small droplets cannot go further than a specific distance from the source before getting pulled into the sink. Larger droplets can travel further from the source before getting pulled into the sink by virtue of their larger inertia. In each case, their maximum traveled distance is determined analytically. In the presence of gravity, we find that there are three distinct droplet behaviors categorized by their sizes: small, intermediate, and large. Counterintuitively, we find that the droplets with a minimum horizontal range are neither small nor large, but of intermediate size. Furthermore, we show that in conditions of human respiration, these intermediate-sized droplets range in size from a few microns to a few hundred microns. The result that such droplets have a very short range could have important implications for our understanding of the spread of airborne diseases. [Preview Abstract] |
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