Artykuły w czasopismach na temat „Droplets”
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Xu, Jinzhu, Li Jia, Chao Dang, Xinyuan Liu i Yi Ding. "Effects of solid–liquid interaction and mixture concentration on wettability of nano-droplets: Molecular dynamics simulations". AIP Advances 12, nr 10 (1.10.2022): 105313. http://dx.doi.org/10.1063/5.0120656.
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The wetting of droplets plays a critical role in engineering applications. Intensive study on nano-droplets is of great significance in revealing the wetting characteristics of droplets. The wetting behavior of ethanol/water mixture nano-droplets on a smooth substrate was investigated through molecular dynamics simulation in this paper. Five nano-droplets of the ethanol/water mixture with different mass fractions placed on a copper surface with different surface energies were simulated to equilibrium at 298.15 K. The contract angle, wetting limit (the minimum and the maximum surface tension of droplets make the surface completely wetted or completely non-wetted by the droplet), and density distribution at the solid–liquid interface of the nano-droplet were analyzed. The effects of ethanol concentration and solid–liquid interaction (corresponding to the droplet’s surface tension and the substrate’s surface energy, respectively) on droplet wettability were intensely discussed. Results revealed that the contact angle of nano-droplets decreased with the increase in ethanol concentration and the interaction between droplets and the substrate. In addition, the critical and ultimate surface tension increased with the increase in the substrate surface energy. The peak density values of the droplets were proportional to the interaction between the droplets and substrate and not related to the droplet concentration. The research also indicated that solid substrates with different surface energies and droplets with various components affected the contact angle of droplets in different ways: the former not only increased the surface tension of droplets at the solid–liquid interface but also increased the separation energy of solids and droplets, while the latter only had a great influence on the surface tension of droplets at the solid–liquid interface.
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Choi, Woorak, i Sungchan Yun. "Behavior of Compound Materials on Superhydrophobic Cylinders: Effects of Droplet’s Size and Interface Angle". Korean Journal of Metals and Materials 62, nr 3 (5.03.2024): 222–28. http://dx.doi.org/10.3365/kjmm.2024.62.3.222.
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Compound droplets can consist of two or more immiscible substances sharing an interface. Among such droplets, the low-viscosity component of Janus droplets can exhibit peculiar bouncing behavior on nonwettable surfaces. There have been recent advances in droplet control technologies, however the impact dynamics of droplets on complex surfaces, and strategies to control their behavior, have not been extensively studied. This study employs the volume of fluid method to analyze the effects of Janus droplet size and the initial interface angle on the dynamics of the two fluidic components in droplets on superhydrophobic cylinders. Janus droplets are composed of low-viscosity (W-) and high-viscosity liquid (G-component). The dynamic characteristics of Janus droplets are investigated as a function of Weber number (<i>We</i>), initial interface angle, the ratio of the droplet’s diameter to the cylinder’s diameter, and viscosity ratio (α). Numerical models provide a regime map of the separation ratio of Janus droplets based on We and α, and the influence of droplet size on asymmetric bouncing is discussed. This study also examines the threshold We at which separation begins after impact, varying with droplet size and α. In addition, the shape evolutions of the droplets are discussed for various initial interface angles to understand the bouncing behavior and separation efficiency. This study is expected to provide valuable strategies for controlling droplet behavior and separation in applications such as liquid purification, rheology, and solidification.
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Hasegawa, Koji, Ayumu Watanabe, Akiko Kaneko i Yutaka Abe. "Coalescence Dynamics of Acoustically Levitated Droplets". Micromachines 11, nr 4 (26.03.2020): 343. http://dx.doi.org/10.3390/mi11040343.
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The contactless coalescence of a droplet is of paramount importance for physical and industrial applications. This paper describes a coalescence method to be used mid-air via acoustic levitation using an ultrasonic phased array system. Acoustic levitation using ultrasonic phased arrays provides promising lab-on-a-drop applications, such as transportation, coalescence, mixing, separation, evaporation, and extraction in a continuous operation. The mechanism of droplet coalescence in mid-air may be better understood by experimentally and numerically exploring the droplet dynamics immediately before the coalescence. In this study, water droplets were experimentally levitated, transported, and coalesced by controlled acoustic fields. We observed that the edges of droplets deformed and attracted each other immediately before the coalescence. Through image processing, the radii of curvature of the droplets were quantified and the pressure difference between the inside and outside a droplet was simulated to obtain the pressure and velocity information on the droplet’s surface. The results revealed that the sound pressure acting on the droplet clearly decreased before the impact of the droplets. This pressure on the droplets was quantitatively analyzed from the experimental data. Our experimental and numerical results provide deeper physical insights into contactless droplet manipulation for futuristic lab-on-a-drop applications.
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Zhang, Yixin, Ruolin Dong, Honghui Shi i Jinhong Liu. "Experimental Investigations on the Deformation and Breakup of Hundred-Micron Droplet Driven by Shock Wave". Applied Sciences 13, nr 9 (29.04.2023): 5555. http://dx.doi.org/10.3390/app13095555.
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This study examines the process of a 240 µm droplet breakup under a shock wave through experiments using a double-pulse laser holographic test technique on a shock tube. The technique allowed for high-resolution data to be obtained at the micron-nanosecond level, including the Weber number distribution of deformation and breakup modes for droplets of different sizes and loads. Results were compared with larger droplets at the same Weber number, revealing that higher Weber numbers result in more difficulty in droplet breakup, longer deformation times, and increased deformation behavior. At low Weber numbers within the critical range, changes in droplet diameter affect the Rayleigh–Taylor waves and alter the droplet’s characteristics. The study also investigates the laws and reasons behind windward displacement variation for hundred-micron droplets at different Weber numbers over time.
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Theodorou, Nicolas T., Alexandros G. Sourais i Athanasios G. Papathanasiou. "Simulation of Electrowetting-Induced Droplet Detachment: A Study of Droplet Oscillations on Solid Surfaces". Materials 16, nr 23 (23.11.2023): 7284. http://dx.doi.org/10.3390/ma16237284.
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The electrowetting-induced detachment of droplets from solid surfaces is important for numerous applications in the fields of heat transfer and fluid mechanics. The forced oscillations of droplets on solid surfaces and their ability to detach are studied. In this study, the process is efficiently simulated by implementing a powerful methodology developed by our team. Our results agree with experiments showing that optimal detachment, in terms of actuation energy, is achieved when the application of voltage is synchronized with the spreading time of the droplet. Under these conditions, the droplet oscillates with a period close to that of a mirrored Rayleigh droplet. The relationship between the droplet’s oscillation period and its physical properties is examined. During voltage-droplet synchronization, the droplet’s ability to detach depends mostly on its contact angle, its viscosity, and the applied voltage. An energy analysis is also conducted, revealing how energy is supplied to the droplet by electrowetting-induced detachment.
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Dembia, Christopher Lee, Yu Cheng Liu i C. Thomas Avedisian. "AUTOMATED DATA ANALYSIS FOR CONSECUTIVE IMAGES FROM DROPLET COMBUSTION EXPERIMENTS". Image Analysis & Stereology 31, nr 3 (5.09.2012): 137. http://dx.doi.org/10.5566/ias.v31.p137-148.
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A simple automated image analysis algorithm has been developed that processes consecutive images from high speed, high resolution digital images of burning fuel droplets. The droplets burn under conditions that promote spherical symmetry. The algorithm performs the tasks of edge detection of the droplet’s boundary using a grayscale intensity threshold, and shape fitting either a circle or ellipse to the droplet’s boundary. The results are compared to manual measurements of droplet diameters done with commercial software. Results show that it is possible to automate data analysis for consecutive droplet burning images even in the presence of a significant amount of noise from soot formation. An adaptive grayscale intensity threshold provides the ability to extract droplet diameters for the wide range of noise encountered. In instances where soot blocks portions of the droplet, the algorithm manages to provide accurate measurements if a circle fit is used instead of an ellipse fit, as an ellipse can be too accommodating to the disturbance.
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Lyu, Sijia, Varghese Mathai, Yujie Wang, Benjamin Sobac, Pierre Colinet, Detlef Lohse i Chao Sun. "Final fate of a Leidenfrost droplet: Explosion or takeoff". Science Advances 5, nr 5 (maj 2019): eaav8081. http://dx.doi.org/10.1126/sciadv.aav8081.
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When a liquid droplet is placed on a very hot solid, it levitates on its own vapor layer, a phenomenon called the Leidenfrost effect. Although the mechanisms governing the droplet’s levitation have been explored, not much is known about the fate of the Leidenfrost droplet. Here we report on the final stages of evaporation of Leidenfrost droplets. While initially small droplets tend to take off, unexpectedly, the initially large ones explode with a crack sound. We interpret these in the context of unavoidable droplet contaminants, which accumulate at the droplet-air interface, resulting in reduced evaporation rate, and contact with the substrate. We validate this hypothesis by introducing controlled amounts of microparticles and reveal a universal 1/3-scaling law for the dimensionless explosion radius versus contaminant fraction. Our findings open up new opportunities for controlling the duration and rate of Leidenfrost heat transfer and propulsion by tuning the droplet’s size and contamination.
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Yoon, Dong, Daiki Tanaka, Tetsushi Sekiguchi i Shuichi Shoji. "Size-Dependent and Property-Independent Passive Microdroplet Sorting by Droplet Transfer on Dot Rails". Micromachines 9, nr 10 (11.10.2018): 513. http://dx.doi.org/10.3390/mi9100513.
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A fully passive microdroplet sorting method is presented in this paper. On the rails with dot patterns, the droplets were sorted in different ways depending on their size. However, the effect of droplet properties on the threshold size of the sorting was eliminated. The droplet positions on two railways and the Laplace pressure of the droplets on the dot patterns allowed selective droplet transfer according to size. Different gaps between the rails altered the threshold size of the transfer. However, the threshold size was independent of the droplet’s surface tension and viscosity because the droplet transfer utilized only the droplet position and Laplace pressure without lateral flow to sort targets. This feature has a high potential for bio/chemical applications requiring categorization of droplet targets consisting of various mixtures as pre- or post-elements.
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Hein, Michael, Michael Moskopp i Ralf Seemann. "Flow field induced particle accumulation inside droplets in rectangular channels". Lab on a Chip 15, nr 13 (2015): 2879–86. http://dx.doi.org/10.1039/c5lc00420a.
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We present accumulation of sedimenting particles/cells within elongated droplets. Particle patterns evolve with droplet velocity, as explained by a topological change of the internal flow and the droplet's outer shape.
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Ochowiak, Marek, Zdzisław Bielecki, Michał Bielecki, Sylwia Włodarczak, Andżelika Krupińska, Magdalena Matuszak, Dariusz Choiński, Robert Lewtak i Ivan Pavlenko. "The D2-Law of Droplet Evaporation When Calculating the Droplet Evaporation Process of Liquid Containing Solid State Catalyst Particles". Energies 15, nr 20 (16.10.2022): 7642. http://dx.doi.org/10.3390/en15207642.
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The review presents the D2-law of droplet evaporation, which is used to describe the spraying process involving the evaporation of droplets. This law, the subject of numerous publications, can be successfully applied to describe the droplet evaporation process under various conditions, including the calculations of the process of feeding the boiler with a liquid that contains catalyst particles. To date, not a lot of work has been devoted to this issue. The paper is a continuation of previous research concerning the spraying of liquids with a catalyst, which improves the efficiency of the process. The conducted analysis showed that the experimental data from previously published work are very compatible with the data obtained from the D2-law of droplet evaporation. At the standard speed of about 20 m/s of an aerosol flowing through a dust duct, droplets in the stream should be observed up to a distance of 1 m from the outlet of the apparatus supplying the system. Under such flow conditions, a droplet’s lifetime must be above 0.05 s. The dependence between a droplet’s lifetime and its diameter and temperature was determined. The obtained results confirmed that the effective droplet diameter is above 30 µm. Such droplets must be generated and then fed to the boiler for the catalyst to work properly. This law is an engineering approach to the problem, which uses relatively simple model equations in order to determine the evaporation time of a droplet.
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Zamboni, R., A. Zaltron, D. Ferraro i C. Sada. "Droplet transition from non-axisymmetric to axisymmetric shape: Dynamic role of lubrication film in a rectangular microfluidic channel". Physics of Fluids 34, nr 12 (grudzień 2022): 122014. http://dx.doi.org/10.1063/5.0123900.
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In the past 20 years, droplet microfluidics is burgeoning in many chemical and biological applications due to the unique capability of droplets to act as confined containers. Confinement is ensured even in the case of squeezed droplets within microchannels much smaller than droplet volumes due to the presence of a lubrication thin film that prevents contact between droplets and the channel walls. The thickness of the lubrication film depends on the dynamics of the entire microfluidic system, affecting the actual droplet's shape and velocity. Therefore, this film is extensively studied to obtain insight into the dynamics of flowing droplets, especially when confined in small channels. Circular cross section channels are the most studied for their axial symmetry, but practical applications present most likely non-axisymmetric channels, as a result of fabrication processes, such as soft lithographic rectangular channels. The latter showed unique transitional morphological behavior of droplets, which assumes an axisymmetric or non-axisymmetric shape during their flow inside a non-axisymmetric channel, depending on the lubrication film. This work gives a comprehensive experimental characterization of the dynamics of the lubrication film during the droplet shape transition. We settled on a novel approach based on the optical diffraction of a localized light beam provided by two-facing optical waveguides integrated with the microfluidics circuit. The technique allows for studying the dynamics of flowing droplets and their relationship with the lubrication film thickness. Additionally, this experimental system enables a precise definition of two regimes of lubrication film, and the critical capillary number at which the transition occurs.
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Parmigiani, Andrea, Paolo Roberto Di Palma, Sébastien Leclaire, Faraz Habib i Xiang-Zhao Kong. "Characterization of Transport-Enhanced Phase Separation in Porous Media Using a Lattice-Boltzmann Method". Geofluids 2019 (14.05.2019): 1–13. http://dx.doi.org/10.1155/2019/5176410.
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Phase separation of formation fluids in the subsurface introduces hydrodynamic perturbations which are critical for mass and energy transport of geofluids. Here, we present pore-scale lattice-Boltzmann simulations to investigate the hydrodynamical response of a porous system to the emergence of non-wetting droplets under background hydraulic gradients. A wide parameter space of capillary number and fluid saturation is explored to characterize the droplet evolution, the droplet size and shape distribution, and the capillary-clogging patterns. We find that clogging is favored by high capillary stress; nonetheless, clogging occurs at high non-wetting saturation (larger than 0.3), denoting the importance of convective transport on droplet growth and permeability. Moreover, droplets are more sheared at low capillary number; however, solid matrix plays a key role on droplet’s volume-to-surface ratio.
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Ma, Yu Po, Xiang Rong Li, Xiang Yuan Wang i Fu Shui Liu. "An Experimental Study on Diesel Fuel Droplets Coupling Evaporation". Advanced Materials Research 383-390 (listopad 2011): 3068–76. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.3068.
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With the continuous improvement of power density,in the process of diesel fuel evaporation in cylinder, the interaction between droplets continues to grow. In order to study the mutual influence in the process of droplets evaporation, the evaporation phenomenas of single droplet, double-droplet and multi-droplet were studied experimentally in this paper. Firstly the influence of background temperature on single droplet evaporation rate was contrasted to verify the reasonableness of the experimental system. And then the influence of number of droplets and distance between droplets was compared and elicited the value of evaporation rate for each experimental condition. It can be found that when the number of droplets increases, the evaporation rate of droplets decreases; when the distance between droplets decreases, the evaporation rate of droplets also reduced.
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HUANG, S., J. POTVIN i C. REBBI. "SURFACE FREE ENERGY OF HADRONIC AND GLUONIC DROPLETS FROM LATTICE QCD". International Journal of Modern Physics C 03, nr 05 (październik 1992): 931–38. http://dx.doi.org/10.1142/s0129183192000592.
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We present the results of a computation of the surface tension on hadronic and gluonic droplets in finite temperature quenched lattice QCD. The surface free energy was obtained by integrating the average action along a path in coupling space corresponding to growing and melting a spherical droplet of a given radius. So far droplets of radius 4, 5 and 8 (in lattice units) have been considered. After discussing ambiguities in the definition of the surface tension due to a droplet’s finite size and thick interface, we compare our results with the Bag model study of Mardor and Svetitsky. Our calculations appear to confirm qualitatively their prediction of a negative surface tension for hadronic droplets with small radii. A similar result is found for gluonic droplets, in contrast however with the Bag model. We also compare our results with the recent lattice simulation of Kajantie, Karkkainen and Rummukainen.
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Duchamp, Margaux, Marion Arnaud, Sara Bobisse, George Coukos, Alexandre Harari i Philippe Renaud. "Microfluidic Device for Droplet Pairing by Combining Droplet Railing and Floating Trap Arrays". Micromachines 12, nr 9 (6.09.2021): 1076. http://dx.doi.org/10.3390/mi12091076.
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Droplet microfluidics are characterized by the generation and manipulation of discrete volumes of solutions, generated with the use of immiscible phases. Those droplets can then be controlled, transported, analyzed or their content modified. In this wide droplet microfluidic toolbox, no means are available to generate, in a controlled manner, droplets co-encapsulating to aqueous phases. Indeed, current methods rely on random co-encapsulation of two aqueous phases during droplet generation or the merging of two random droplets containing different aqueous phases. In this study, we present a novel droplet microfluidic device to reliably and efficiently co-encapsulate two different aqueous phases in micro-droplets. In order to achieve this, we combined existing droplet microfluidic modules in a novel way. The different aqueous phases are individually encapsulated in droplets of different sizes. Those droplet populations are then filtered in order to position each droplet type towards its adequate trapping compartment in traps of a floating trap array. Single droplets, each containing a different aqueous phase, are thus paired and then merged. This pairing at high efficiency is achieved thanks to a unique combination of floating trap arrays, a droplet railing system and a droplet size-based filtering mechanism. The microfluidic chip design presented here provides a filtering threshold with droplets larger than 35 μm (big droplets) being deviated to the lower rail while droplets smaller than 20 μm (small droplets) remain on the upper rail. The effects of the rail height and the distance between the two (upper and lower) rails were investigated. The optimal trap dimensions provide a trapping efficiency of 100% for small and big droplets with a limited double trapping (both compartments of the traps filled with the same droplet type) of 5%. The use of electrocoalescence enables the generation of a droplet while co-encapsulating two aqueous phases. Using the presented microfluidic device libraries of 300 droplets, dual aqueous content can be generated in less than 30 min.
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Jiang, Tsung Leo, i Huei-Huang Chiu. "Combustion of a Fuel Droplet Surrounded by Oxidizer Droplets". Journal of Heat Transfer 113, nr 4 (1.11.1991): 959–65. http://dx.doi.org/10.1115/1.2911228.
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The interaction between a burning fuel droplet and satellite oxidizer droplets is studied analytically. The effects of droplet spacing and droplet size ratio on the flame configuration of a burning fuel droplet with a satellite oxidizer droplet are analyzed in a high-temperature oxidizing environment by using the bispherical coordinate system. Three combustion modes including normal combustion, conjugate combustion, and composite combustion are identified at appropriate droplet size ratio and droplet spacing. The burning rate of the fuel droplet is found to be greater than that of an isolated burning fuel droplet, and to increase with the decreasing distance between two droplets. This result has shown a positive effect on the interaction between fuel and oxidizer droplets, in contrast to that of two interacting fuel droplets where the burning rate decreases with decreasing droplet spacing. The combustion configuration of a fuel droplet surrounded by six satellite oxidizer droplets symmetrically is also examined by the method of images. The flame that encloses the fuel droplet is found to be “compressed” and distorted to a nonspherical shape due not only to the group effect among oxidizer droplets but also to the interaction of bipropellant droplets. The results indicate that the burning rate of a fuel droplet increases and the flame size decreases significantly as a result of an increased supply of oxidizer vapor provided by the surrounding oxidizer droplets. Therefore properly optimized bipropellant combustion is potentially able to achieve a desired combustion performance with a much smaller combustor than a conventional spray burner.
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Jin, Yi, Zhuqing Ren, Yanjie Tan, Pengxiang Zhao i Jian Wu. "Motility Plays an Important Role in the Lifetime of Mammalian Lipid Droplets". International Journal of Molecular Sciences 22, nr 8 (7.04.2021): 3802. http://dx.doi.org/10.3390/ijms22083802.
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The lipid droplet is a kind of organelle that stores neutral lipids in cells. Recent studies have found that in addition to energy storage, lipid droplets also play an important role in biological processes such as resistance to stress, immunity, cell proliferation, apoptosis, and signal transduction. Lipid droplets are formed at the endoplasmic reticulum, and mature lipid droplets participate in various cellular processes. Lipid droplets are decomposed by lipase and lysosomes. In the life of a lipid droplet, the most important thing is to interact with other organelles, including the endoplasmic reticulum, mitochondria, peroxisomes, and autophagic lysosomes. The interaction between lipid droplets and other organelles requires them to be close to each other, which inevitably involves the motility of lipid droplets. In fact, through many microscopic observation techniques, researchers have discovered that lipid droplets are highly dynamic organelles that move quickly. This paper reviews the process of lipid droplet motility, focusing on explaining the molecular basis of lipid droplet motility, the factors that regulate lipid droplet motility, and the influence of motility on the formation and decomposition of lipid droplets. In addition, this paper also proposes several unresolved problems for lipid droplet motility. Finally, this paper makes predictions about the future research of lipid droplet motility.
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Biferale, L., C. Meneveau i R. Verzicco. "Deformation statistics of sub-Kolmogorov-scale ellipsoidal neutrally buoyant drops in isotropic turbulence". Journal of Fluid Mechanics 754 (30.07.2014): 184–207. http://dx.doi.org/10.1017/jfm.2014.366.
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AbstractSmall droplets in turbulent flows can undergo highly variable deformations and orientational dynamics. For neutrally buoyant droplets smaller than the Kolmogorov scale, the dominant effects from the surrounding turbulent flow arise through Lagrangian time histories of the velocity gradient tensor. Here we study the evolution of representative droplets using a model that includes rotation and stretching effects from the surrounding fluid, and restoration effects from surface tension including a constant droplet volume constraint, while assuming that the droplets maintain an ellipsoidal shape. The model is combined with Lagrangian time histories of the velocity gradient tensor extracted from direct numerical simulations (DNS) of turbulence to obtain simulated droplet evolutions. These are used to characterize the size, shape and orientation statistics of small droplets in turbulence. A critical capillary number is identified associated with unbounded growth of one or two of the droplet’s semi-axes. Exploiting analogies with dynamics of polymers in turbulence, the critical capillary number can be predicted based on the large deviation theory for the largest finite-time Lyapunov exponent quantifying the chaotic separation of particle trajectories. Also, for subcritical capillary numbers near the critical value, the theory enables predictions of the slope of the power-law tails of droplet size distributions in turbulence. For cases when the viscosities of droplet and outer fluid differ in a way that enables vorticity to decorrelate the shape from the straining directions, the large deviation formalism based on the stretching properties of the velocity gradient tensor loses validity and its predictions fail. Even considering the limitations of the assumed ellipsoidal droplet shape, the results highlight the complex coupling between droplet deformation, orientation and the local fluid velocity gradient tensor to be expected when small viscous drops interact with turbulent flows. The results also underscore the usefulness of large deviation theory to model these highly complex couplings and fluctuations in turbulence that result from time integrated effects of fluid deformations.
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Dobson, Chandler, Claudia Zielke, Ching Pan, Cameron Feit i Paul Abbyad. "Method for Passive Droplet Sorting after Photo-Tagging". Micromachines 11, nr 11 (28.10.2020): 964. http://dx.doi.org/10.3390/mi11110964.
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We present a method to photo-tag individual microfluidic droplets for latter selection by passive sorting. The use of a specific surfactant leads to the interfacial tension to be very sensitive to droplet pH. The photoexcitation of droplets containing a photoacid, pyranine, leads to a decrease in droplet pH. The concurrent increase in droplet interfacial tension enables the passive selection of irradiated droplets. The technique is used to select individual droplets within a droplet array as illuminated droplets remain in the wells while other droplets are eluted by the flow of the external oil. This method was used to select droplets in an array containing cells at a specific stage of apoptosis. The technique is also adaptable to continuous-flow sorting. By passing confined droplets over a microfabricated trench positioned diagonally in relation to the direction of flow, photo-tagged droplets were directed toward a different chip exit based on their lateral movement. The technique can be performed on a conventional fluorescence microscope and uncouples the observation and selection of droplets, thus enabling the selection on a large variety of signals, or based on qualitative user-defined features.
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Chen, Shengde, Yubin Lan, Zhiyan Zhou, Fan Ouyang, Guobin Wang, Xiaoyu Huang, Xiaoling Deng i Shengnan Cheng. "Effect of Droplet Size Parameters on Droplet Deposition and Drift of Aerial Spraying by Using Plant Protection UAV". Agronomy 10, nr 2 (1.02.2020): 195. http://dx.doi.org/10.3390/agronomy10020195.
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In the field of pesticide spraying, droplet size is one of the most important factors affecting droplet deposition and drift. In order to study the effect of different droplet size parameters on droplet deposition distribution and drift of aerial spraying by using plant protection UAV, an aerial spraying test with the same spraying rate and different size droplets in rice canopy was carried out by using multi-rotor unmanned aerial vehicles (UAV) and four TEEJET nozzles with different orifice sizes (these droplets with a volume median diameter (VMD) of 95.21, 121.43, 147.28, and 185.09 μm, respectively), and the deposition distribution and penetration of droplets in the target area and the drift distribution of droplets in the non-target area were compared and analyzed. The results showed that the deposition distribution and penetration of droplets in the target area and the drift distribution of droplets in the non-target area were influenced by the droplet size. The droplet deposition rate in the upper and lower rice canopies were increased in the target area with the increase of droplet size. The penetration results of droplets also increased with the increase of droplet size, and that of droplets with a VMD of 185.09 μm was the best, reaching 38.13%. The average values of the cumulative drift rate of droplets in the rice canopy in the four tests were 73.87%, 50.26%, 35.91%, and 23.06%, respectively, and the cumulative drift rate and the drift distance of droplets decreased with the increase of droplet size, which indicated that the increase of droplet size can effectively reduce droplet drift. It demonstrated that the droplet size is one of the most important factors affecting droplet deposition and drift for pesticide spraying by plant protection UAV, and for the application of plant protection UAV with extra-low volume spraying, the use of droplets with VMD less than 160 μm should be avoided and a more than 10 m buffer zone should be considered downwind of the spraying field to avoid drug damage caused by pesticide drift. The results have fully revealed the effect of droplet size parameters on droplet deposition and drift of aerial spraying. Moreover, the influence of the wind field below the rotors on the distribution of droplet deposition was surmised and analyzed from the perspective of plant protection UAV. It is important for optimizing the droplet parameters of aerial spraying, increasing the spraying efficiency, and realizing precision agricultural aviation spray.
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Cheng, Yonghong, Xu Zhao, Michael Danikas, Despoina Christantoni i Pavlos Zairis. "A Study of the Behaviour of Water Droplets Under the Influence of Uniform Electric Field in Epoxy Resin Samples". Journal of Electrical Engineering 63, nr 3 (1.05.2012): 196–200. http://dx.doi.org/10.2478/v10187-012-0029-3.
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A Study of the Behaviour of Water Droplets Under the Influence of Uniform Electric Field in Epoxy Resin SamplesWater droplets on the surface of epoxy resin samples were investigated under the influence of uniform electric fields. Several parameters of water droplets were investigatedwrtthe flashover voltage of the epoxy resin samples, such as water conductivity, droplet volume, number of droplets as well as the positioning of the droplets regarding the electrodes. The droplet behavior is affected by the above mentioned parameters. Perhaps the most striking conclusion is that the flashover voltage depends more on the positioning of the dropletswrtthe electrodes than on the droplet volume and/or number of droplets.
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Chi, Baihong, Zhiwei Jiao i Weimin Yang. "Design and experimental study on the freeform fabrication with polymer melt droplet deposition". Rapid Prototyping Journal 23, nr 3 (18.04.2017): 633–41. http://dx.doi.org/10.1108/rpj-03-2015-0028.
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Purpose 3D printing based on additive manufacturing has advantages in manufacturing products with high geometrical complexity. However, there are many limitations to print plastic products with the existing commercial 3D printers. The polymer materials processing industry needs new devices which can satisfy the trend of processing individual units and small batch sizes of plastic parts. Design/methodology/approach In this study, a freeform fabrication system with the method of polymer melt droplet deposition is proposed. The performance of this system under different conditions was studied by changing the operating parameters. Furthermore, the dimensional uniformity of droplets and their deposition process are analyzed, and a plastic sample was fabricated with this system as an example. Findings The results show a clear correlation between the processing parameters and the droplet diameter. In the experiment for examining the dimensional uniformity of the droplet, the droplets become spindles, and there appears a melt filament between the droplets. The variation of the droplet’s diameters is within 5 per cent. Furthermore, a successfully processed rectangular plastic sample verified the feasibility of this technology for the printing of plastic products. Originality/value A freeform fabrication system with polymer melt droplet deposition is proposed, which can process a wide variety of materials in the form of standard granulates like injection molding or extrusion. Based on the principle of droplet deposition, multi-component or colorful materials can be printed.
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Morozov, Matvey, i Sébastien Michelin. "Self-propulsion near the onset of Marangoni instability of deformable active droplets". Journal of Fluid Mechanics 860 (11.12.2018): 711–38. http://dx.doi.org/10.1017/jfm.2018.853.
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Experimental observations indicate that chemically active droplets suspended in a surfactant-laden fluid can self-propel spontaneously. The onset of this motion is attributed to a symmetry-breaking Marangoni instability resulting from the nonlinear advective coupling of the distribution of surfactant to the hydrodynamic flow generated by Marangoni stresses at the droplet’s surface. Here, we use a weakly nonlinear analysis to characterize the self-propulsion near the instability threshold and the influence of the droplet’s deformability. We report that, in the vicinity of the threshold, deformability enhances self-propulsion of viscous droplets, but hinders propulsion of drops that are roughly less viscous than the surrounding fluid. Our asymptotics further reveals that droplet deformability may alter the type of bifurcation leading to symmetry breaking: for moderately deformable droplets, the onset of self-propulsion is transcritical and a regime of steady self-propulsion is stable; while in the case of highly deformable drops, no steady flows can be found within the asymptotic limit considered in this paper, suggesting that the bifurcation is subcritical.
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Han, Zhirong, Jiangtao Si i Dawei Wu. "Contrast Icing Wind Tunnel Tests between Normal Droplets and Supercooled Large Droplets". Aerospace 9, nr 12 (18.12.2022): 844. http://dx.doi.org/10.3390/aerospace9120844.
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In order to compare and analyze the similarities and differences between normal droplet icing shapes and supercooled large droplet icing shapes, SADRI carried out normal droplet and supercooled large droplet icing wind tunnel tests in the NRC−AIWT icing wind tunnel. Taking the typical glaze ice in normal droplet icing conditions as the reference, the freezing drizzle and freezing rain icing tests under the supercooled large droplet conditions were carried out. The test results show that compared with normal droplets, the ice horn height of supercooled large droplets decreases with the increase in droplet particle size, and even the ice horn characteristics are not obvious when the icing condition is freezing rain. At the same time, the range and height of rough element ice shape after the main ice horn of supercooled large droplets are significantly larger and higher than those of the normal droplets, while the difference in the rough element in different supercooled large droplet icing conditions is small.
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Chen, Yanyan, Yusheng Liang i Mengyuan Chen. "The deformation and breakup of a droplet under the combined influence of electric field and shear flow". Fluid Dynamics Research 53, nr 6 (1.12.2021): 065504. http://dx.doi.org/10.1088/1873-7005/ac3893.
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Abstract A lattice Boltzmann and finite-difference hybrid method is used to simulate the droplet deformation and breakup under the combined action of shear flow and electric field. The hybrid method is first used to validate for the droplet deformation in the combined action of shear flow and electric field. It is then used to simulate the droplet deformation and breakup in two different electric systems. Results of prolate droplets show that the droplet height and deformation both increase with increasing electric capillary number ( C a E ). In addition, for the breakup mode of prolate droplets, increasing C a E makes the long axis of the droplet incline more towards the wall electrodes and droplet breaks up into more daughter droplets. Results of oblate droplets show that the droplet height decreases with increasing C a E . However, the droplet deformation first decreases and then increases with increasing C a E , and its minima occurs at C a E = 0.01 . For the breakup mode of oblate droplets, the droplet deforms into a more oblate shape with a longer neck and finally breakup into more daughter droplets with increasing C a E .
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Zhu, Zhongrui, Delan Zhu i Maosheng Ge. "The Spatial Variation Mechanism of Size, Velocity, and the Landing Angle of Throughfall Droplets under Maize Canopy". Water 13, nr 15 (30.07.2021): 2083. http://dx.doi.org/10.3390/w13152083.
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Larger diameter and velocity and smaller landing angle of sprinkler irrigation droplets are more likely to cause soil splash and erosion. However, the mechanism of crop canopy influence on the physical parameters of sprinkler droplets is unknown. In this study, with the landing angle of sprinkler irrigation droplets as the independent variable and maize plants (Zea mays L.) as the research object, an indoor sprinkler irrigation experiment was carried out. The effects of maize canopy and variation in sprinkler irrigation droplets landing angle on the value and spatial distribution pattern of size, the velocity, and the landing angle of throughfall droplets was analyzed. In addition, the spatial variation patterns of throughfall droplets size, velocities’ distribution, and individual droplet’s speed, kinetic energy were also explored. The results showed that maize canopy and the decreasing of the sprinkler irrigation droplet landing angle had a positive and obvious effect on reducing the size and velocity of penetrating rain droplets. However, the throughfall droplets’ landing angles were only small variations. When the landing angle of sprinkler irrigation droplets was >45°, the spatial distribution of throughfall droplets size and velocity corresponded well with the canopy structure and leaf projection area of maize, i.e., the further away from the maize stalk, the larger the size and velocity of throughfall droplets. Nevertheless, if the landing angle of sprinkler irrigation droplets was <45°, the spatial distribution mentioned above was mainly affected by droplets landing angle. The spatial variation of throughfall droplets’ size and velocities at different measurement points was attributed to the change of the larger droplets’ volume proportion and the equivalent velocity. Although the maize leaves had a certain degree of perturbation effect on the velocities and kinetic energy of the larger kinetic energy droplets, the flight path of these drops did not alter significantly. The results of this research will be of practical value in guiding the development of a new sprayer and the optimum selection of sprinkler heads.
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Egley, Grant H., James E. Hanks i C. Douglas Boyette. "Invert Emulsion Droplet Size and Mycoherbicidal Activity ofColletotrichum truncatum". Weed Technology 7, nr 2 (czerwiec 1993): 417–24. http://dx.doi.org/10.1017/s0890037x00027822.
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When formulated and sprayed in an invert emulsion (IE), conidia of the mycoherbicide,Colletotrichum truncatum, controlled hemp sesbania in the absence of dew. To optimize hemp sesbania control, formulation droplet size influence upon the pathogen's germination and pathogenicity was investigated. Conidia germination in manually produced IE droplets decreased from 46% to 5% as droplet diameter decreased from 2700 to 900μm. Droplet size did not affect appressoria formation. On a per conidium basis, 900-μm droplets were more pathogenic to detached hemp sesbania leaves than were 2100-μm droplets. An air-assist spray system produced droplet spectra with volume median diameters of 421 and 104μm, respectively. The spectrum of smaller droplets covered the target better than did that of larger droplets. When applied to whole hemp sesbania plants in greenhouse trials, conidia in the smaller and larger droplet spectra gave 90 and 94% control, respectively. Sufficient conidia germinated in IE droplets of a variety of sizes to control hemp sesbania excellently.
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Wang, Zixiong, Xiaoyi Wang, Guotao Zhang i Fangling Liang. "Numerical study of the seepage behavior of droplets in porous materials". Journal of Physics: Conference Series 2760, nr 1 (1.05.2024): 012069. http://dx.doi.org/10.1088/1742-6596/2760/1/012069.
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Abstract This article analyzes the spread and infiltration dynamic process of liquid droplets on the surface of porous materials and establishes a mathematical model of dynamic changes in droplets. To accurately describe the dynamic effects of droplet flow, a mathematical model of droplet dynamics was developed by applying the level-set method, and the seepage process of the droplets was also analyzed numerically. The effects of a series of control parameters on the droplet percolation process are analyzed, and the pore degree of porous materials performed a numerical study of the droplet deformation process. We observe the spread and infiltration process of liquid droplets in porous materials models. It was found that there is a competitive relationship between diffusion and penetration of droplets. The depth of penetration of droplets decreases with increasing viscosity and increases with increasing porosity. The results of the study help to understand the seepage behavior of the droplet on the surface of the porous material.
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Khain, A., V. Arkhipov, M. Pinsky, Y. Feldman i Ya Ryabov. "Rain Enhancement and Fog Elimination by Seeding with Charged Droplets. Part I: Theory and Numerical Simulations". Journal of Applied Meteorology 43, nr 10 (1.10.2004): 1513–29. http://dx.doi.org/10.1175/jam2131.1.
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Abstract A new method of droplet collision acceleration, with the purpose of rain enhancement and fog elimination, is proposed. According to the method, some fraction of the droplets is taken from clouds (or fog) themselves, charged, and then injected back into clouds (or fog). To verify the efficiency of the method, a novel model has been developed, allowing simulation of droplet spectrum evolution by collision in case a certain fraction of the droplets in a droplet spectrum is charged. Simulations of droplet spectra evolution include several steps: (a) The forces arising between charged and neutral droplets, as well as between charged droplets, are calculated as the function of the value of the charges, droplet size, and distance between droplets. It is shown that because of the induction effect, significant attraction forces arise between charged and neutral droplets. (b) The results obtained have been used to calculate the collision efficiencies between charged and neutral, as well between charged droplets. As a result, a “four dimensional” table of the collision efficiencies (the collision efficiency is the function of the droplet size and charge) was calculated. The collision efficiencies between charged and neutral droplets turn out to be significantly higher than the pure gravity-induced values. (c) To accomplish these simulations, a novel numerical method of solving the stochastic collision equation has been developed. Cloud droplets are described by a two-dimensional size distribution function in which droplets are characterized by both their mass and charge. (d) This model, with the implemented table of the collision efficiencies, has been used to simulate droplet spectra evolution in clouds and fog in case some fraction of these droplets was charged. Simulations of the effects of seeding by charged droplets have been performed. Evolution of initially narrow droplet size spectra (typical of extremely continental clouds in highly smoky air), in the case of seeding and under natural conditions, has been simulated. It was shown that although a natural droplet spectrum does not develop and no raindrops are formed, the injection of just a small fraction of charged particles rapidly triggered the collision process and lead to raindrop formation a few minutes after the injection. Significant acceleration of raindrop formation has been found in the case of a maritime wide-droplet spectrum. Simulations of fog seeding were conducted using droplet spectra distributions of typical fog. Seeding by charged fog droplets of one or both polarities was simulated. In both cases a significant increase in fog visibility was found. The advantages of the seeding method proposed are discussed.
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Wang, Zhibin, Tianli Sun, Zhongwei Yang, Guo Zhu i Hongyan Shi. "Interactions between Two Deformable Droplets in Tandem Fixed in a Gas Flow Field of a Gas Well". Applied Sciences 11, nr 23 (25.11.2021): 11220. http://dx.doi.org/10.3390/app112311220.
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Knowing the droplet-deformation conditions, the droplet-breakup conditions, and the drag force in the interaction between two droplets with a high Reynolds number is of importance for tracking droplet movement in the annular flow field of a gas well. The interactions between two droplets with a high Reynolds number in a tandem arrangement fixed in flowing gas was investigated. The volume of fluid (VOF) method was used to model the droplets’ surface structure. Two different body forces were exerted on both droplets to hold them suspended at a fixed location, which eliminated the effect of droplet acceleration or deceleration on the drag and decreased the amount of computation required. The exerted body forces were calculated using the Newton iteration procedure. The interactions between the two droplets were analyzed by comparison with the simulation results of a single isolated droplet. The effect of the separation distance on the drag force was investigated by changing the separation spacing. The simulation results showed that for droplets with a small separating space between them, the dynamics of the downstream droplet were influenced significantly by the upstream droplet. The drag coefficient of the downstream droplet decreased considerably to a small, even negative, value, especially for droplets with higher Weber numbers and smaller initial separating spaces between them, while the drag force of the upstream droplet was influenced only slightly. In addition, a formula for predicting the final drag coefficient of the downstream droplet was devised.
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Pei, Xiangyu, Yikan Meng, Yueling Chen, Huichao Liu, Yao Song, Zhengning Xu, Fei Zhang, Thomas C. Preston i Zhibin Wang. "Technical note: Characterization of a single-beam gradient force aerosol optical tweezer for droplet trapping, phase transition monitoring, and morphology studies". Atmospheric Chemistry and Physics 24, nr 9 (6.05.2024): 5235–46. http://dx.doi.org/10.5194/acp-24-5235-2024.
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Abstract. Single particle analysis is essential for a better understanding of the particle transformation process and to predict its environmental impact. In this study, we developed an aerosol optical tweezer (AOT) Raman spectroscopy system to investigate the phase state and morphology of suspended aerosol droplets in real time. The system comprises four modules: optical trapping, reaction, illumination and imaging, and detection. The optical trapping module utilizes a 532 nm laser and a 100 × oil immersion objective to stably trap aerosol droplets within 30 s. The reaction module allows us to adjust relative humidity (RH) and introduce reaction gases into the droplet levitation chamber, facilitating experiments to study liquid–liquid phase transitions. The illumination and imaging module employs a high-speed camera to monitor the trapped droplets, while the detector module records Raman scattering light. We trapped sodium chloride (NaCl) and 3-methyl glutaric acid (3-MGA) mixed droplets to examine RH-dependent morphology changes. Liquid–liquid phase separation (LLPS) occurred when RH was decreased. Additionally, we introduced ozone and limonene/pinene to generate secondary organic aerosol (SOA) particles in situ, which collided with the trapped droplet and dissolved in it. To determine the trapped droplet's characteristics, we utilized an open-source program based on Mie theory to retrieve diameter and refractive index from the observed whispering gallery modes (WGMs) in Raman spectra. It is found that mixed droplets formed core–shell morphology when RH was decreased, and the RH dependence of the droplets' phase transitions generated by different SOA precursors varied. Our AOT system serves as an essential experimental platform for in situ assessment of morphology and phase state during dynamic atmospheric processes.
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Stilianakis, Nikolaos I., i Yannis Drossinos. "Dynamics of infectious disease transmission by inhalable respiratory droplets". Journal of The Royal Society Interface 7, nr 50 (29.04.2010): 1355–66. http://dx.doi.org/10.1098/rsif.2010.0026.
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Transmission of respiratory infectious diseases in humans, for instance influenza, occurs by several modes. Respiratory droplets provide a vector of transmission of an infectious pathogen that may contribute to different transmission modes. An epidemiological model incorporating the dynamics of inhalable respiratory droplets is developed to assess their relevance in the infectious process. Inhalable respiratory droplets are divided into respirable droplets, with droplet diameter less than 10 µm, and inspirable droplets, with diameter in the range 10–100 µm: both droplet classes may be inhaled or settle. Droplet dynamics is determined by their physical properties (size), whereas population dynamics is determined by, among other parameters, the pathogen infectivity and the host contact rates. Three model influenza epidemic scenarios, mediated by different airborne or settled droplet classes, are analysed. The scenarios are distinguished by the characteristic times associated with breathing at contact and with hand-to-face contact. The scenarios suggest that airborne transmission, mediated by respirable droplets, provides the dominant transmission mode in middle and long-term epidemics, whereas inspirable droplets, be they airborne or settled, characterize short-term epidemics with high attack rates. The model neglects close-contact transmission by droplet sprays (direct projection onto facial mucous membranes), retaining close-contact transmission by inspirable droplets.
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Lin, Jeng-Liang, i Heping Zhu. "Fading Activities of Herbicidal Droplets Amended with Emulsifiable Spray Adjuvants on Cucurbitaceous Leaves". Transactions of the ASABE 61, nr 6 (2018): 1881–88. http://dx.doi.org/10.13031/trans.13061.
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Abstract. Understanding reactions of surfactant-amended droplets on difficult-to-wet weed surfaces could help develop application strategies to increase herbicide efficacy. Behaviors of herbicidal droplets containing different emulsifiable anti-evaporation spray adjuvants were investigated by characterizing 250 and 450 µm herbicidal droplet dispersion and fading time on cucurbitaceous leaves placed inside a 20°C chamber at 30% and 60% relative humidity (RH). Droplet maximum coverage area increased with droplet size but not with RH, while droplet fading time increased with both droplet size and RH. Despite 450 µm droplets having greater maximum coverage area than 250 µm droplets, the larger droplets had higher fading rates and lower ratios of maximum coverage area to droplet volume. Droplet maximum coverage area and fading time on leaves were affected by adding spray adjuvants to the herbicide-only solution. The Uptake surfactant was more effective than the other two surfactants (AntiEvap+BS1000 and Enhance) in increasing droplet maximum coverage area and fading time. Compared to the herbicide-only solution, addition of Uptake surfactant to the herbicide solution could increase maximum coverage area by 68% and 52% for 250 and 450 µm droplets, respectively, but addition of AntiEvap+BS1000 or Enhance surfactants did not show significant increase. Similarly, addition of Uptake surfactant to the herbicide-only solution increased droplet fading times by 11.1% and 13.2% at 30% and 60% RH, respectively, for 250 µm droplets and by 34.7% and 2.8% at 30% and 60% RH, respectively, for 450 µm droplets. In contrast, addition of AntiEvap+BS1000 surfactant reduced fading time, and addition of Enhance surfactant did not significantly affect fading time. Therefore, appropriate selection of spray adjuvants for herbicide applications could significantly influence droplet deposit behaviors on cucurbitaceous leaves, leading to improved effectiveness of weed control. Keywords: Herbicide application, Spray deposition, Spray droplet, Surfactant, Weed control.
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Huang, Zheng Yong, Jian Li, Fei Peng Wang, Huan Huan Xia i Mao Chang Li. "The Collision Behavior of Droplets Splitted from a Droplet that Rebounded on Super-Hydrophobic Surface". Applied Mechanics and Materials 723 (styczeń 2015): 968–71. http://dx.doi.org/10.4028/www.scientific.net/amm.723.968.
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Droplet rebounding on super-hydrophobic surfaces is critical to suppress pollution flashover (i.e. enhancement of pollution flashover-voltage) and to reduce ice accumulation on insulators. This paper presents a novel way to reduce water accumulation on surface via the elastic collision between droplets splitted from a droplet that has rebounded from super-hydrophobic surface. The water-mass that contacted with surface will be reduced resultantly. The influence of hydrophobicity of the surface on contact time and spreading time of water droplets are discussed. The collision behavior between the splitted droplets is indicated by the surface charge that was induced by the rebounding droplets on super-hydrophobic surface. Experimental results show that the super-hydrophobic surface endows water droplets with shorter contact time, spreading time than those values obtained on a bare glass. Specific Web and Reynolds numbers can lead to the elastic rebounding between water droplets, delaying the water contact with the super-hydrophobic surface. The contact electrification between the rebounded droplet and the super-hydrophobic surface renders the droplet charged, thus determines the collision behavior of the splitted droplets that born from the rebounded droplet.
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Imani, Gloire, Lei Zhang, Chao Xu, Munezero Ntibahanana, Hai Sun i Jun Yao. "Finite droplets vs long droplets: Discrepancy in release conditions in a microscopic constricted channel". Physics of Fluids 35, nr 3 (marzec 2023): 032101. http://dx.doi.org/10.1063/5.0139025.
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Conditions of release of trapped droplets in constricted channels are of great significance in various domains, including microfluidic development and enhanced oil recovery. In our previous studies, a detailed and quantitative analysis of the threshold pressure needed to release a droplet from a constricted channel has been performed. However, droplets may exist in real applications as long droplets, which may exhibit different behavior than finite droplets. Therefore, in this study, direct numerical simulations, combining the fluid flow equations and the phase-field method, have been conducted on three-dimensional constrained channels to investigate discrepancies in release conditions of finite droplets and long droplets. The results have shown that for a finite droplet, the maximum pressure increases with the increase in the contact angle, whereas for a long droplet, the maximum pressure is almost the same both in the water-wet and neutral-wet conditions. Effects of droplet size on the release pressure have also been studied. For the finite droplet and at the water-wet condition (θ = 45°), the minimum release pressure increases linearly with the droplet length, while for the long droplet at similar conditions, the minimum release pressure does not change much as the length of the droplet increases. Furthermore, the release pressure decreases with the increased tapering angle.
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Zhong, Yuan, Haicun Du, Ying Zhang, Yue Chen, Qiang Liu i Jie Huang. "Experimental research on dynamic characteristics of viscous droplets impacting rough solid surfaces at different temperatures". Canadian Journal of Physics 97, nr 12 (grudzień 2019): 1288–300. http://dx.doi.org/10.1139/cjp-2018-0494.
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In view of different factors that influence dynamic behavior of a droplet impacting a solid surface, high-speed photography technology was used to capture oscillation processes and splash forms after changing seven kinds of physical properties, droplets impacting different roughness and temperature walls, and with different velocities and sizes. A physical model was established, and the theoretical value correlation of maximum spreading factor was derived to compare the theoretical analysis with experimental results. The effects of viscosity, surface tension, impact velocity, diameter of droplet, roughness, and temperature of the substrates on movement characteristics during the droplet’s impact on the wall surface were investigated. As the research indicates, the rebound and oscillatory phenomena of the fluid become more obvious with an increase in surface tension, and viscous force restricts the spreading of droplets. The higher the impact velocity, the greater the spreading factor at the same time, and the more pronounced the splashing phenomenon will be. The growth rate of maximum spreading factor (βmax) increases at first and then decreases with increasing initial diameter (d0) of the droplets. The smaller the d0, the more consistent the experimental results with the analytical solutions. The equilibrium contact angle (θe) of the droplet increases with surface roughness (Ra), whereas the surface wettability degrades. θe decreases with rising wall temperature. The increase of Ra promotes the “finger-like edge” and the splash motion of droplets; moreover, the critical velocity of splash declines with Ra. The optimum temperature (Tc) of a droplet impacting the high-temperature wall reduces with a decrease of Re. Furthermore, the greater the difference between wall temperature and Tc, the more significantly βmax changes. Droplet spreading is hindered on the low-temperature wall, and the lower Re is, the smaller the decrease in amplitude of βmax with dropping wall temperature.
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Malinowski, Robert, Ivan P. Parkin i Giorgio Volpe. "Nonmonotonic contactless manipulation of binary droplets via sensing of localized vapor sources on pristine substrates". Science Advances 6, nr 40 (wrzesień 2020): eaba3636. http://dx.doi.org/10.1126/sciadv.aba3636.
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Droplet motion on surfaces influences phenomena as diverse as microfluidic liquid handling, printing technology, and energy harvesting. Typically, droplets are set in motion by inducing energy gradients on a substrate or flow on their free surface. Current configurations for controllable droplet manipulation have limited applicability as they rely on carefully tailored wettability gradients and/or bespoke substrates. Here, we demonstrate the nonmonotonic contactless long-range manipulation of binary droplets on pristine substrates due to the sensing of localized water vapor sources. The droplet-source system presents an unexpected off-centered equilibrium position. We capture the underlying mechanism behind this symmetry breaking with a simplified model based on the full two-dimensional functional form of the surface tension gradient induced by the source on the droplet’s free surface. This insight on the transport mechanism enables us to demonstrate its versatility for applications by printing, aligning, and reacting materials controllably in space and time on pristine substrates.
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Huang, Qiaogao, Ya Zhang i Guang Pan. "Dynamic Behaviors and Energy Transition Mechanism of Droplets Impacting on Hydrophobic Surfaces". Discrete Dynamics in Nature and Society 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/8517309.
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The wettability of hydrophobic surfaces and the dynamic behaviors of droplets impacting on hydrophobic surfaces are simulated using a lattice Boltzmann method, and the condition for the rebound phenomenon of droplets impacting on solid surfaces is analyzed. The results show that there is a linear relationship between the intrinsic contact angle and the interaction strength of fluid-wall particles. For hydrophobic surfaces with the same intrinsic contact angle, the micromorphology can increase the surface hydrophobicity, especially the hierarchical micromorphology. The dynamic behaviors of droplets impacting on solid surfaces are affected by the wettability. The surface hydrophobicity is stronger, and the rebound phenomenon occurs easier. If the droplet’s kinetic energy is greater than the sum of the surface energy and the minimum conversion gravitational potential energy when the spreading and shrinking finish, the rebound phenomenon will occur. As the hydrophobic surface’s viscous dissipation is much smaller than the hydrophilic surface’s, the droplet still has high kinetic energy after the spreading and shrinking, which is advantageous to rebound for droplets.
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He, Guo, Xiao Chuan Wang i Yan Fei Li. "Effects of Droplets' Collision on Heat and Mass Transfer between High-Temperature Gas and Micron Water Droplets". Key Engineering Materials 609-610 (kwiecień 2014): 1386–91. http://dx.doi.org/10.4028/www.scientific.net/kem.609-610.1386.
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The heat and mass transfer process between gas and micron water droplets is complicated. During the process, the collision of droplets can affect the evaporation rate of droplets, and the heat and mass transfer between two phases as well. Unsteady numerical simulation was done in this paper to investigate the effect of droplets collision on the heat and mass transfer. The results show that after the water droplets collide and combine together, the total heat transfer area decreases, thus the accelerated rate of droplet temperature drops. As a result, the unsteady time of droplet temperature rising with considering droplets collision in calculation is longer than that of without considering droplets collision. After droplets collide and combine together, the evaporation rate drops, thus the droplets survival time and time for evaporating completely are extended. The steady gas temperature with droplets collision is higher slightly than that without droplets collision, which indicates that the droplets collision affect the results by using numerical prediction. Against the experimental data, the predicted results with droplets collision are more believable than that without collision. Considering the droplets collision and combination, the change rate of the droplets diameter drops, thus the gas velocity picks up slowly.
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Balakirev S. V., Kirichenko D. V., Chernenko N. E., Shandyba N. A., Eremenko M. M. i Solodovnik M. S. "Study of the effect of ultra-low arsenic flux on the formation of In(As)/GaAs nanostructures by droplet epitaxy". Physics of the Solid State 64, nr 8 (2022): 949. http://dx.doi.org/10.21883/pss.2022.08.54609.345.
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In this paper, we present the results of studying the influence of arsenic pressure in the range of ultra-low values (10-7-10-6 Pa) on the processes of modification of In/GaAs(001) droplets with various initial sizes obtained by droplet epitaxy. We experimentally demonstrate that exposure of droplets to the ultralow arsenic flux makes it possible to reduce the droplet size to subcritical sizes while maintaining the initially specified surface density. The exposure of droplet nanostructures in the arsenic flux can be accompanied only by a decrease in their size, which is more typical for droplets obtained at large amounts of indium deposited material. For droplets with a smaller initial size, the formation of rings along the perimeter of the initial droplets and holes inside the rings is typical along with the droplet reduction. We also reveal that the dependence of the relative volume of droplets subjected to diffusion decay in the arsenic flux becomes more significant with a decrease in their initial size. Keywords: droplet epitaxy, nanostructures, In(As)/GaAs, arsenic flux.
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Балакирев, С. В., Д. В. Кириченко, Н. Е. Черненко, Н. А. Шандыба, М. М. Ерёменко i М. С. Солодовник. "Исследование влияния ультрамалого потока мышьяка на процессы формирования наноструктур In(As)/GaAs методом капельной эпитаксии". Физика твердого тела 64, nr 8 (2022): 943. http://dx.doi.org/10.21883/ftt.2022.08.52688.345.
Pełny tekst źródłaStreszczenie:
In this paper, we present the results of studying the influence of arsenic pressure in the range of ultra-low values (10^-7-10^-6 Pa) on the processes of modification of In/GaAs(001) droplets with various initial sizes obtained by droplet epitaxy. We experimentally demonstrate that exposure of droplets to the ultralow arsenic flux makes it possible to reduce the droplet size to subcritical sizes while maintaining the initially specified surface density. The exposure of droplet nanostructures in the arsenic flux can be accompanied only by a decrease in their size, which is more typical for droplets obtained at large amounts of indium deposited material. For droplets with a smaller initial size, the formation of rings along the perimeter of the initial droplets and holes inside the rings is typical along with the droplet reduction. We also reveal that the dependence of the relative volume of droplets subjected to diffusion decay in the arsenic flux becomes more significant with a decrease in their initial size.
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Yao, S. C., L. E. Hochreiter i K. Y. Cai. "Dynamics of Droplets Impacting on Thin Heated Strips". Journal of Heat Transfer 110, nr 1 (1.02.1988): 214–20. http://dx.doi.org/10.1115/1.3250454.
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Experiments were conducted with water droplets impacting on the edge of thin steel strips that were heated to beyond the Leidenfrost temperature. High-speed movies were taken and analyzed and showed that the shattered droplets were generally bimodal in size distribution. The volume ratio of these two size groups of generated droplets, the mean diameter of droplets, and the ejection angles and velocities of shattered droplets are shown as a function of incoming droplet Weber number, the ratio of incoming droplet diameter to strip thickness, and the offset of the droplet relative to the strip. The data are presented in nondimensional form and correlations are provided for the mean diameter of the shattered droplets. The theoretical limiting conditions of a droplet impacting normally to a large plate and cutting by a strip of zero thickness are analyzed. The present results are compared with those of the limiting conditions. The application to a nuclear reactor spacer grid behavior during two-phase dispersed flow is discussed.
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Wang, Yiting, Lijuan Qian, Zhongli Chen i Fang Zhou. "Coalescence of Binary Droplets in the Transformer Oil Based on Small Amounts of Polymer: Effects of Initial Droplet Diameter and Collision Parameter". Polymers 12, nr 9 (9.09.2020): 2054. http://dx.doi.org/10.3390/polym12092054.
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In engineering applications, the coalescence of droplets in the oil phase dominates the efficiency of water-oil separation. To improve the efficiency of water-oil separation, many studies have been devoted to exploring the process of water droplets colliding in the oil phase. In this paper, the volume of fluid (VOF) method is employed to simulate the coalescence of water droplets in the transformer oil based on small amounts of polymer. The influences of the initial diameter and collision parameter of two equal droplets on droplet deformation and coalescence time are investigated. The time evolution curves of the dimensionless maximum deformation diameter of the droplets indicate that the larger the droplet diameter, the more obvious the deformation from central collisions. As the collision parameter increases, the contact area of the two droplets, as well as the kinetic energy that is converted into surface energy, decreases, resulting in an increase in droplet deformation. Furthermore, the effects of the initial droplet diameter and collision parameter on coalescence time are also investigated and discussed. The results reveal that as the initial droplet diameter and collision parameter increase, the droplet coalescence time increases.
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Xu, Jinzhu, Li Jia, Xinyuan Liu, Chao Dang i Yi Ding. "Pseudo-Leidenfrost phenomenon of low surface tension droplet induced by external aerodynamic field". AIP Advances 13, nr 4 (1.04.2023): 045114. http://dx.doi.org/10.1063/5.0138821.
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Droplet regulation has significant application potential in many fields; however, conventional controlling methods make it difficult to effectively control low surface tension droplets. Inspired by the Leidenfrost phenomenon, a pseudo-Leidenfrost system was established innovatively through micro-airflow rather than evaporated vapor to lift a droplet. Both experimental and numerical studies were carried out to investigate the pseudo-Leidenfrost effect of the FC3283 (perfluorotripropylamine) droplet. By FC3283, it is an extremely low surface tension working medium with thermal stability at room temperature. The oscillation of the droplet in the vertical direction was analyzed by tracking the position of the droplet centroid. The velocity of micro-airflow and pressure distributions at the bottom surface of the droplet, which were similar to the Leidenfrost phenomenon, were revealed. The mechanical analysis of the FC3283 droplet in a pseudo-Leidenfrost period was analyzed. Besides, the pseudo-Leidenfrost phenomenon of FC40 [FC-40 FluorinertTM Electronic Liquid] droplets with various Weber number was investigated. Weber number conditions for droplets triggering the pseudo-Leidenfrost phenomenon were revealed. The results showed that the motion of pseudo-Leidenfrost droplets in a period could be divided into three stages: falling, hovering, and rising. In the hovering stage, the Laplace force played an important role, which was the main reason for the rebound of the droplet, while the role of the aerodynamic force was to keep the droplet on the surface of the gas film. The Weber number had a significant influence on the pseudo-Leidenfrost phenomenon: droplets with a small Weber number tended to be absorbed by the micropores, while a too large Weber number would cause droplets to suspend or even leave. This study is helpful for controlling low surface tension droplets and laying a foundation for the transportation of low surface tension droplets.
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Sawaguchi, Erina, Ayumi Matsuda, Kai Hama, Masafumi Saito i Yoshiyuki Tagawa. "Droplet levitation over a moving wall with a steady air film". Journal of Fluid Mechanics 862 (8.01.2019): 261–82. http://dx.doi.org/10.1017/jfm.2018.952.
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In isothermal non-coalescence behaviours of a droplet against a wall, an air film of micrometre thickness plays a crucial role. We experimentally study this phenomenon by letting a droplet levitate over a moving glass wall. The three-dimensional shape of the air film is measured using an interferometric method. The mean curvature distribution of the deformed free surface and the distributions of the lubrication pressure are derived from the experimental measurements. We vary experimental parameters, namely wall velocity, droplet diameter and viscosity of the droplets, over a wide range; for example, the droplet viscosity is varied over two orders of magnitude. For the same wall velocity, the air film of low-viscosity droplets shows little shape oscillation with constant film thickness (defined as the steady state), while that of highly viscous droplets shows a significant shape oscillation with varying film thickness (defined as the unsteady state). The droplet viscosity also affects the surface velocity of a droplet. Under our experimental conditions, where the air film shape can be assumed to be steady, we present experimental evidence showing that the lift force generated inside the air film balances with the droplet’s weight. We also verify that the lubrication pressure locally balances with the surface tension and hydrostatic pressures. This indicates that lubrication pressure and the shape of the free surface are mutually determined. Based on the local pressure balance, we discuss a process of determining the steady shape of an air film that has two areas of minimum thickness in the vicinity of the downstream rim.
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Chang, Feixiang, Hongliang Luo, Panpan Dong, Keiya Nishida, Yoichi Ogata, Ryosuke Hara, Kenji Uchida i Wu Zhang. "Characteristics of Droplet Behaviors during Spray Breakup Process". Sustainability 15, nr 12 (9.06.2023): 9356. http://dx.doi.org/10.3390/su15129356.
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The variation of droplet parameters during the spray breakup process affects the droplet deposition behavior and accurate application. The aim of this study was to experimentally investigate droplet behaviors along the penetration direction with respect to spray propagation. Particle image analysis (PIA) was applied to obtain the characteristics of droplets at three representative stages (namely, initial, quasi-steady, and end stages) after the start of injection (ASOI). The effects of timing and location on the spray characteristics were thoroughly investigated. First, different morphological changes of spray (droplets, ligaments, and bags) during spray breakup were observed. The experimental results show that droplet size and velocity distinctly increase from upstream to downstream at the initial stage. However, at the quasi-steady and end stages, droplet velocities are similar, and the effects of location are not evident. This indicates that location has a significant effect on droplet behaviors at the initial stage. The mean minimum distance (MD) of droplets first increases considerably and then decreases from upstream to downstream, suggesting that the droplets disperse better at midstream. Moreover, the mean MD at the initial stage exceeds that at the quasi-steady and end stages, denoting that the droplets disperse better with time. Finally, the geometric parameter of droplets and the key stage selection are important for predicting the interaction between the droplets and surfaces.
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Ki, Sunghyun, i Dong-Ku Kang. "Gas Crosstalk between PFPE–PEG–PFPE Triblock Copolymer Surfactant-Based Microdroplets and Monitoring Bacterial Gas Metabolism with Droplet-Based Microfluidics". Biosensors 10, nr 11 (11.11.2020): 172. http://dx.doi.org/10.3390/bios10110172.
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The PFPE–PEG–PFPE (Perfluoropolyether-polyethylene glycol-perfluoropolyether) surfactant has been used in droplet-based microfluidics and is known to provide high droplet stability and biocompatibility. Since this surfactant ensures the stability of droplets, droplet-based microfluidic systems have been widely used to encapsulate and analyze various biological components at the single-molecule scale, including viruses, bacteria, nucleic acids and proteins. In this study, we experimentally confirmed that gas crosstalk occurred between droplets formed by fluorinated oil and the PFPE–PEG–PFPE surfactant. E. coli K-12 bacterial cells were encapsulated with Luria–Bertani broth within droplets for the cultivation, and gas crosstalk was identified with neighboring droplets that contain phenol red. Since bacteria produce ammonia gas during its metabolism, penetration of ammonia gas initiates a color change of phenol red-containing droplets. Ammonia gas exchange was also confirmed by reacting ammonium chloride and sodium hydroxide within droplets that encapsulated. Herein, we demonstrate the gas crosstalk issue between droplets when it is formed using the PFPE–PEG–PFPE surfactant and also confirm that the density of droplet barrier has effects on gas crosstalk. Our results also suggest that droplet-based microfluidics can be used for the monitoring of living bacteria by the determination of bacterial metabolites during cultivation.
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Qian, Lijuan, Jingqi Liu, Hongchuan Cong, Fang Zhou i Fubing Bao. "A Numerical Investigation on the Collision Behavior of Unequal-Sized Micro-Nano Droplets". Nanomaterials 10, nr 9 (3.09.2020): 1746. http://dx.doi.org/10.3390/nano10091746.
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Micro-nano droplet collisions are fundamental phenomena in the applications of nanocoating, nano spray, and microfluidics. Detailed investigations of the process of the droplet collisions under higher Weber are still lacking when compared with previous research studies under a low Weber number below 120. Collision dynamics of unequal-sized micro-nano droplets are simulated by a coupled level-set and volume of fluid (CLSVOF) method with adaptive mesh refinement (AMR). The effects of the size ratio (from 0.25 to 0.75) and different initial collision velocities on the head-on collision process of two unequal-sized droplets at We = 210 are studied. Complex droplets will form the filament structure and break up with satellite droplets under higher Weber. The filament structure is easier to disengage from the complex droplet as the size ratio increases. The surface energy converting from kinetic energy increases with the size ratio, which promotes a better spreading effect. When two droplets keep the constant relative velocity, the motion tendency of the droplets after the collision is mainly dominated by the large droplet. On one hand, compared with binary equal-sized droplet collisions, a hole-like structure can be observed more clearly since the initial velocity of a large droplet decreases in the deformation process of binary unequal-sized droplets. On the other hand, the rim spreads outward as the initial velocity of the larger droplet increases, which leads to its thickening.
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Zhang, Jian, Xinhai Yu i Shan-Tung Tu. "Lattice Boltzmann Simulation on Droplet Flow through 3D Metal Foam". Processes 7, nr 12 (22.11.2019): 877. http://dx.doi.org/10.3390/pr7120877.
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The hydrodynamics of droplets passing through metal foam is investigated using the lattice Boltzmann method (LBM). The accurate 3D porous structure for the simulation is generated by X-ray micro-computed tomography. The simulated results are in good agreement with the experimental ones using high-speed video. The simulated results show that for droplets passing metal foam, there is a critical capillary number, Cac (around 0.061), above which the droplet continues to deform until it breaks up. The simulated results show that the capillary number, droplet size, pores diameter, and thickness of metal foam have the significant effect of droplets deforming and breaking up when the droplets pass through the metal foam. To avoid the calescence of two droplets at the inlet zone of the metal foam, the distance between droplets should be larger than three times the diameter of the droplet.
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Fallast, A., A. R. Rapf, A. Tramposch i W. Hassler. "Kinetic and thermal simulation of water droplets in icing wind tunnels". CEAS Aeronautical Journal 13, nr 1 (13.11.2021): 181–98. http://dx.doi.org/10.1007/s13272-021-00558-y.
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AbstractWithin the certification process of aircraft, tests under specific icing conditions are required. For such safety relevant tests—which are performed under defined and repeatable test conditions—specially equipped Icing Wind Tunnels (IWT) are required. In such IWTs, supercooled water droplets are created with the aid of a spray system injecting pre-tempered water droplets of specific diameters into the free stream air flow. Especially tests with a droplet size up to 2mm (Supercooled Large Droplets - SLDs) are of great importance. SLDs are difficult to generate under laboratory conditions in IWT since usually the available droplet flight time from the injection location to the impact position on the test object is insufficient to reliably cool down a droplet at least to freezing temperature. To investigate the limitations associated with the application of SLD, the current work provides a method to allow detailed insight into the behavior of droplets on the path from the injection spray nozzle to the test section. In this work a state space model of a single droplet is derived that combines the kinetic aspects, thermal properties as well as the governing differential equations for motion, convective heat transfer at the droplet surface and heat conduction inside the droplet. Beside the states for the droplet’s position and velocity in space, the state space vector comprises various fluid and thermodynamic parameters. The droplet-internal temperature distribution is modelled by a discrete one-dimensional spherical shell model that also incorporates the aggregate phase (freezing mass fraction) at each shell node. This approach allows, therefore, the simulation of potential droplet phase change processes (freezing/melting) as well. With the model at hand, the influence of various boundary conditions (initial droplet temperature, flow field, ambient air temperature, etc.) can be determined and evaluated. As a result, concrete measures to achieve a desired operating condition (e.g. droplet temperature at the test object) for various model assumptions can be derived. In addition, the simulation model facilitates the prediction of the droplet diameter threshold for ensuring a supercooled state upon the impact on the test object. The governing theoretical influences are described, and various simulation results for representative test conditions that occur at the Rail-Tec-Arsenal (RTA) in Vienna are presented.