Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F11: Spreading and Evaporation of Binary Drops |
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Chair: Justin Burton, Emory University Room: Georgia World Congress Center B216 |
Monday, November 19, 2018 8:00AM - 8:13AM |
F11.00001: Development of stereoscopic three-dimensional particle tracking velocimetry using machine learning technique Han Seo Ko, Yeonghyeon Gim, Dong Kyu Jang, Dong Kee Sohn, Hyoungsoo Kim A three-dimensional Particle Tracking Velocimetry (3D-PTV) technique is a method to extract velocity data inside target fluid. Unlike a three-dimensional Particle Image Velocimetry (3D-PIV) technique, the 3D-PTV technique focuses on three-dimensional movement of particles inside the target. Thus, it is appropriate to analyze sedimentation patterns during droplet evaporation phenomena. In this study, the 3D-PTV technique was applied to visualize evaporation flow pattern inside a binary mixture droplet. The technique was developed by a machine learning technique and verified by a numerical simulation. Then, the three-dimensional flow structure inside the droplet was obtained. The droplet consists of DI water, ethanol, and particles with a diameter of 15 µm. The images of particles inside the droplet were captured by two high-speed cameras. The images were revised by the image processing procedure, and successfully used for reconstructing the three-dimensional trajectories of the particles inside the droplet. |
Monday, November 19, 2018 8:13AM - 8:26AM |
F11.00002: Analysis of self-assembled microstructures from evaporated drops of bourbon whiskey Adam D. Carrithers, Martin J. Brown VI, Stuart J. Williams A web-like pattern of self-assembled microstructures remain after the evaporation of drop of diluted bourbon whiskey. Interestingly, these patterns are different for each bourbon brand as these “fingerprints” are a function of bourbon intrinsic properties (maturation, mash bill, etc.). This presentation will discuss the influence of varying environmental factors such as temperature and humidity on the repeatability of these patterns. Digital image analysis is used to measure the influence of these extrinsic properties. Findings will be used to correlate the pattern with the bourbon’s authenticity. Results will guide future work for in-the-field counterfeit tests as well as a crude measure of maturation. |
Monday, November 19, 2018 8:26AM - 8:39AM |
F11.00003: Particles disappear, phase segregation is shown Hyoungsoo Kim, Howard A. Stone In fluid dynamics, tracer particles are commonly used for flow visualization because many fluids are transparent. In this study, we introduce a unusual experiment where seeded fluorescent polystyrene particles are dissolved at a specific concentration ratio between two liquid components, which we use to identify molecular segregation in a binary mixture droplet during evaporation. This selective evaporation phenomenon has never been observed in experimental results. In addition, we develop a theoretical model in good agreement with the experimental results. We expect that understanding of the evaporation mechanism of a multi-component liquid droplet will provide some insights to construct mixture components depending upon various physicochemical applications, such as ink-jet printing, spray coating, and droplet-based microfluidics for biochemical and biomedical applications. |
Monday, November 19, 2018 8:39AM - 8:52AM |
F11.00004: Experimental Study of Substrate Temperature Effect on the Behavior of Droplet Evaporation of Binary Mixtures Ali Alshehri, Hossein P Kavehpour Evaporation of droplets has caught a lot of scientific attention due to its significance in numerous industrial applications, such as heat pipes, evaporative self-assembly, and capillary tubes to name a few. Many researchers have shown that the maximum evaporation rate takes place very close to the three-phase contact line. The evaporation rate of the droplet plays an important role to control the evolution of the droplet, i.e. base diameter as well as contact angle change with time. Literature survey showed that very few papers have examined the substrate temperature and therefore the evaporation rate effect on the droplet evolution. This work investigates experimentally the droplet evolution of binary mixtures under different substrate temperatures. Infrared thermography is utilized as a tool to study the temperature variation of the droplet surface as evaporation takes place. |
Monday, November 19, 2018 8:52AM - 9:05AM |
F11.00005: Evaporating binary droplets: significant impact of natural convection below the millimeter scale Christian Diddens, Yaxing Li, Herman Wijshoff, Michel Versluis, Detlef Lohse While the evaporation of pure sessile droplets is well understood, the situation drastically changes when the droplet composition is constituted by a mixture of different liquids, as e.g. in typical applications like inkjet printing. On the basis of finite element simulations and experiments, we investigate the possible flow types. Finally, we are able to predict the flow in the droplets by phase-diagrams in terms of the Rayleigh and Marangoni numbers. |
Monday, November 19, 2018 9:05AM - 9:18AM |
F11.00006: Density-Driven Flows in Evaporating Binary Liquid Droplets Fouzia F. Ouali, Andrew M.J. Edwards, Patrick S. Atkinson, Sammy Cheung, Haida Liang, David J. Fairhurst We report a pioneering development of rotatable optical coherence tomography to image the flow patterns in tilted evaporating binary liquid droplets deposited on substrates with contact angles between 20ο and 100ο. The evaporation of the droplets proceeds in three distinct stages: chaotic (Stage I), convective (Stage II) and outward radial flow (Stage III). Stage I is characterised by random and strongly circulating vortices, attributed to solutal Marangoni flows driven by the preferential evaporation of the more volatile component (ethanol). Stage III is characterised by an outward capillary flow of the less volatile single component droplet (water). Our measurements conclusively demonstrate that, in contrast to the accepted view and conventional calculations of the Marangoni and Rayleigh numbers, the convective flow (Stage II) is driven by density-driven solutal Rayleigh convection. We also use gas chromatography to determine the time evolution of the concentration of the more volatile component within the droplet and confirm that a simple analysis of volume data provides the same information. Finally, we establish a flow phase diagram demonstrating the conditions under which the different stages occur. |
Monday, November 19, 2018 9:18AM - 9:31AM |
F11.00007: Spreading and evaporation of sessile drops comprising binary mixtures Adam G L Williams, George Karapetsas, Pedro J Saenz, Omar K Matar, Khellil Sefiane, Prashant Valluri Spreading and evaporation of a binary mixture sessile drop from a heated substrate is a complex process governed by the delicate balance between capillary stresses, evaporation, hydrodynamic flow, mass diffusion and surface tension, with both thermal and solutal Marangoni stresses present. We examine the behaviour and stability of volatile wetting ethanol-water drops deposited onto heated substrates using both experimental and modelling approaches. Our one-sided model uses lubrication theory to obtain a base state which we then perturb and assess the stability using a linear stability analysis evoking the quasi-steady-state approximation. Evolution equations are derived for the film height, temperature and concentration field assuming that the mixture comprises two ideally mixed volatile components with surface tension linearly dependent on temperature and concentration. Contact line movement is permitted by releasing the drop over a precursor film, avoiding the singularity at the contact line. Our simulations and experiments indicate that concentration gradients give rise to super-spreading and contact line instabilities, not previously seen in pure fluids. Results from our model qualitatively and quantitatively agree with experiments. |
Monday, November 19, 2018 9:31AM - 9:44AM |
F11.00008: Evaporation-Triggered Segregation of Sessile Binary Droplets Yaxing Li, Pengyu Lv, Christian Diddens, Huanshu Tan, Herman Wijshoff, Michel Versluis, Detlef Lohse Droplet evaporation of multicomponent droplets is essential for various physiochemical applications, e.g., in inkjet printing, spray cooling, and microfabrication. In this work, we observe and study the phase segregation of an evaporating sessile binary droplet, consisting of a miscible mixture of water and a surfactantlike liquid (1,2-hexanediol). The phase segregation (i.e., demixing) leads to a reduced water evaporation rate of the droplet, and eventually the evaporation process ceases due to shielding of the water by the nonvolatile 1,2-hexanediol. Visualizations of the flow field by particle image velocimetry and numerical simulations reveal that the timescale of water evaporation at the droplet rim is faster than that of the Marangoni flow, which originates from the surface tension difference between water and 1,2-hexanediol, eventually leading to segregation. |
Monday, November 19, 2018 9:44AM - 9:57AM |
F11.00009: Vapour transfer into ethanol drops drying in a humid atmosphere Yutaku Kita, Daniel Orejon, Yasuyuki Takata, Khellil Sefiane We report adsorption-absorption and/or condensation of water vapour into ethanol drops during their evaporation in humid air. Combining drop profile measurements with Gas Chromatography allows to directly quantify the amounts of ethanol evaporated and of water intake over time. Increases in the rate of ethanol evaporation and in that of the water intake are observed at higher relative humidity (RH). The increase in ethanol evaporation at higher RH is attributed to the greater diffusion coefficient of ethanol into moist air than dry air. Moreover, the drop surface temperature is found to fall below the dew point due to evaporative cooling in at higher RH, leading to more water condensation onto the drop. The heat released by the water vapour intake gives rise to a higher temperature at the drop surface and hence a greater driving force for evaporation. Based on the experiments, we propose an empirical correlation of the water intake combined with the diffusion model for drop evaporation, which agrees remarkably well with experimental observations. |
Monday, November 19, 2018 9:57AM - 10:10AM |
F11.00010: Coupled thermal transport and mass diffusion during vapor absorption at the droplet scale Zhenying Wang, Daniel Orejon, Prashant Valluri, Yasuyuki Takata, Khellil Sefiane This study focuses on the coupled heat and mass transfer during vapor absorption at the droplet scale. Driven by the vapor pressure difference between the ambient and the droplet surface, desiccant droplets expand due to water uptake. The droplet growth rate and expansion ratio depend on the ambient temperature and humidity. When looking into the infrared thermography, droplets experience the highest surface temperature right after being deposited. Then drops gradually cool down as heat transfers into the substrate and ambient atmosphere, coupled with the decrease in the vapor absorption rate. The initial temperature rise is due to the fast vapor absorption which proceeds during droplet deposition, and is verified by the order of absorption heat flux in the six conditions. The vapor pressure at the droplet surface is further evaluated taking account of the concentration variation and surface temperature variation, which demonstrates the evolution of driving force for vapor diffusion along with time. Contrast experiments with water droplets show different profile evolution, inverse contact line dynamics, and opposite evaporation cooling effect. Conclusions here help to understand the dehumidification process in more details. |
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