Artykuły w czasopismach na temat „Droplet”
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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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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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Du, Lin, Yuxin Li, Jie Wang, Zijian Zhou, Tian Lan, Dalei Jing, Wenming Wu i Jia Zhou. "Cost-Effective Droplet Generator for Portable Bio-Applications". Micromachines 14, nr 2 (17.02.2023): 466. http://dx.doi.org/10.3390/mi14020466.
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The convenient division of aqueous samples into droplets is necessary for many biochemical and medical analysis applications. In this article, we propose the design of a cost-effective droplet generator for potential bio-chemical application, featuring two symmetric tubes. The new droplet generator revisits the relationship between capillary components and liquid flow rates. The size of generated droplets by prototype depends only on generator dimensions, without precisely needing to control external flow conditions or driving pressure, even when the relative extreme difference in flow rate for generating nL level droplets is over 57.79%, and the relative standard deviation (RSD) of the volume of droplets is barely about 9.80%. A dropper working as a pressure resource is used to verify the rapidity and robustness of this principle of droplet generation, which shows great potential for a wide range of droplet-based applications.
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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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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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Widyatama, Arif, Akmal Irfan Majid, Teguh Wibowo, Deendarlianto Deendarlianto i Samsul Kamal. "EXPERIMENTAL STUDY ON THE PHENOMENA ON THE SUCCESSIVE DROPLETS IMPACTING HOT COPPER SURFAC". Jurnal Penelitian Saintek 24, nr 2 (29.10.2019): 129–42. http://dx.doi.org/10.21831/jps.v24i2.26923.
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This study was aimed at investigating the phenomena and interactions between water droplets and hot metal surfaces using an experimental method. In this study, the droplet was dropped from 50 mm from the top of the metal surface with a frequency of 8.5 droplets per second. The observed droplet diameter was 3.12 mm. The metal used was copper with a surface temperature between 110-240 ° C. High speed video camera with a speed of 2000 fps was used to record visual data. Then the image processing technique was applied to calculate the change in droplet diameter. The results show that at low temperatures, droplets tend to maintain their initial position of contact with fluctuating deformations. While at high temperatures, a bounce phenomenon occurs which results in collisions between droplets being imperfect. Visualization results can reveal the complete change in the droplet geometry in the form of spreading ratio and complete apex height. The temperature of 140° C is the initial transition area for phenomena that result in droplets has no contact with hot surfaces so that the process of heat transfer between surfaces is inhibited.STUDI EKSPERIMEN PADA FENOMENA SUCCESSIVE DROPLETS MENUMBUK PERMUKAAN TEMBAGA PANASPenelitian ini bertujuan untuk mempelajari fenomena dan interaksi antara tetesan air (droplet) dan permukaan logam panas dengan metode eksperimental. Pada penelitian ini, droplet dijatuhkan dari posisi 50 mm dari atas permukaan logam dengan frekuensi 8,5 droplet per detik. Diameter droplet yang diamati sebesar 3,12 mm. Logam yang digunakan adalah tembaga dengan temperatur permukaan di antara 110-240° C. High speed video camera dengan kecepatan 2000 fps digunakan untuk merekam data visual. Teknik image processing diaplikasikan untuk menghitung perubahan diameter droplet. Hasil penelitian menunjukkan bahwa pertama, pada temperatur rendah, droplet cenderung mempertahankan posisi awal kontak dengan perubahan bentuk yang fluktuatif. Kedua, temperatur tinggi, terjadi fenomena bouncing yang mengakibatkan tumbukan antar droplet menjadi tidak sempurna. Hasil visualisasi dapat mengungkap perubahan geometri droplet berupa spreading ratio dan apex height secara lengkap. Dari penelitian ini juga diketahui bahwa temperatur 140°C menjadi daerah transisi awal terjadinya fenomena yang mengakibatkan droplet tidak bersinggungan dengan permukaan panas sehingga proses perpindahan kalor antar permukaan terhambat.
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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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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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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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Jonglearttrakull, P., K. Fushinobu i M. Kadonaga. "Effects of the Thickness of Boundary Layer on Droplet’s Evaporation Rate". Journal of Imaging Science and Technology 64, nr 5 (1.09.2020): 50402–1. http://dx.doi.org/10.2352/j.imagingsci.technol.2020.64.5.050402.
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Abstract The evaporation rate of a droplet was explained in relation to the thickness of the boundary layer and the condition near the droplet’s surface. However, the number of results obtained from experiments is very limited. This study aims to investigate the thickness of the boundary layer of an ethanol‐water mixture droplet and its effect on the evaporation rate by Z-type Schlieren visualization. Single and double droplets are tested and compared to identify the effect of the second droplet on the average and instantaneous evaporation rate. The double droplet’s lifetime is found to be longer than the single droplet’s lifetime. The formation of a larger vapor region on the top of the droplet indicates a higher instantaneous evaporation rate. The thickness of the boundary layer is found to increase with increase in ethanol concentration. Furthermore, a larger vapor distribution area is found in the case of higher ethanol concentration, which explains the faster evaporation rate at higher ethanol concentration.
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Spicer, Patrick T., i Richard W. Hartel. "Crystal Comets: Dewetting During Emulsion Droplet Crystallization". Australian Journal of Chemistry 58, nr 9 (2005): 655. http://dx.doi.org/10.1071/ch05119.
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Liquid oil emulsion droplets can violently dewet their own solid crystals during crystallization as a result of surfactant adsorption. The crystal shape formed is a function of the relative rates of dewetting and crystallization as controlled by surfactant adsorption, cooling rate, and lipid purity. For negligible dewetting rates, crystals nucleate and grow within the droplet. At similar crystallization and dewetting rates, the droplet is propelled around the continuous phase on a crystalline ‘comet tail’ much larger than the original droplet. Rapid dewetting causes the ejection of small discrete crystals across the droplet’s oil–water interface.
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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.
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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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Wibowo, Teguh, Dedet Hermawan, Dedet Hermawan, Agung Prakoso i Agung Prakoso. "EXPERIMENTAL STUDY OF COOLING SPRAY METHOD ONTO INCLINED HEATED SURFACES". Vortex 3, nr 1 (15.01.2022): 40. http://dx.doi.org/10.28989/vortex.v3i1.1164.
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Single droplet impingement onto inclined heated surface is studied experimentally. Droplet in the form of aquades is dropped from a fixed height 70 mm to the metal surface with 45º impact angle. This experiment uses 3 types of metals; Stainless Steel AISI 304, Aluminum Alloy 2024, and Copper. All material surfaces are mirror polished and assumed to have the same surface treatment condition. Surface temperatures are 110 ºC, 150 ºC and 210 ºC to determine droplet behavior characteristics. The droplet has 3.0 mm diameter and 28.5 Weber Number (low impact category). In order to analyze droplet behavior in slow motion high velocity camera 4000 fps (frames per second) is used with image resolution 1024 x 768. Data obtained then processed using MATLAB image processing technique to analyze sequence of images visually and quantitatively to determine several parameters; spreading ratio, dimensionless height and contact time.The results showed droplets have different behavior characteristics even at the same surface temperature. Droplet contact time on the copper surface is shorter than aluminum and stainless steel. This is because droplets experienced bouncing due to film boiling regime takes place earlier. Maximum spreading ratio of stainless-steel surfaces is higher than copper because changes of boiling regime on stainless steel surfaces are slower and droplet is still experiencing spreading on the surface
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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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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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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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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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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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Nakai, Tonau, Takahiro Ueno, Kenji Kanzawa i Tomonobu Goto. "Temperature Dependence of the Lifetime of a Droplet on a Liquid Surface". Journal of Robotics and Mechatronics 23, nr 3 (20.06.2011): 386–92. http://dx.doi.org/10.20965/jrm.2011.p0386.
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When a liquid is dropped onto a surface of the same liquid, the droplet often remains floating on the surface for a while because of the thin air film between the droplet and the surface. We find that the time during which this phenomenon is sustained depends on the temperature of the droplet and surface. In our experiment using silicone oil at a temperature range of 20-150°C, the lifetime of a droplet was found to be longer when the temperature difference between the droplet and surface was larger at the moment of the droplet’s landing. The lifetime was longer for a cold droplet on a hot surface than the opposite case, with the same temperature difference. Time-series measurements of the temperature of the floating droplet revealed that it coalesces with the liquid surface at a certain threshold temperature difference. These results indicate that the lifetime of a droplet is determined by the time it takes the temperature difference to decrease to the threshold.
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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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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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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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Heyn, Christian, i Stefan Feddersen. "Modeling of Al and Ga Droplet Nucleation during Droplet Epitaxy or Droplet Etching". Nanomaterials 11, nr 2 (12.02.2021): 468. http://dx.doi.org/10.3390/nano11020468.
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The temperature dependent density of Al and Ga droplets deposited on AlGaAs with molecular beam epitaxy is studied theoretically. Such droplets are important for applications in quantum information technology and can be functionalized e.g., by droplet epitaxy or droplet etching for the self-assembled generation of quantum emitters. After an estimation based on a scaling analysis, the droplet densities are simulated using first a mean-field rate model and second a kinetic Monte Carlo (KMC) simulation basing on an atomistic representation of the mobile adatoms. The modeling of droplet nucleation with a very high surface activity of the adatoms and ultra-low droplet densities down to 5 × 106 cm−2 is highly demanding in particular for the KMC simulation. Both models consider two material related model parameters, the energy barrier ES for surface diffusion of free adatoms and the energy barrier EE for escape of atoms from droplets. The rate model quantitatively reproduces the droplet densities with ES = 0.19 eV, EE = 1.71 eV for Al droplets and ES = 0.115 eV for Ga droplets. For Ga, the values of EE are temperature dependent indicating the relevance of additional processes. Interestingly, the critical nucleus size depends on deposition time, which conflicts with the assumptions of the scaling model. Using a multiscale KMC algorithm to substantially shorten the computation times, Al droplets up to 460 °C on a 7500 × 7500 simulation field and Ga droplets up to 550 °C are simulated. The results show a very good agreement with the experiments using ES = 0.19 eV, EE = 1.44 eV for Al, and ES = 0.115 eV, EE = 1.24 eV (T≤ 300 °C) or EE = 1.24 + 0.06 (T[°C] − 300)/100 eV (T>300 °C) for Ga. The deviating EE is attributed to a re-nucleation effect that is not considered in the mean-field assumption of the rate model.
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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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Nepomnyashchy, Alexander, i Ilya Simanovskii. "The Influence of Two-Dimensional Temperature Modulation on Floating Droplet Dynamics". Fluids 9, nr 1 (25.12.2023): 6. http://dx.doi.org/10.3390/fluids9010006.
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We investigate the dynamics and instabilities of a droplet that floats on a liquid substrate. The substrate is cooled from below. In the framework of the slender droplet approximation and the precursor model, the problem is studied numerically. Oscillatory and stationary regimes of thermocapillary convection have been observed. The influence of a two-dimensional spatial inhomogeneity of temperature on the droplet dynamics is investigated. The two-dimensional spatial temperature inhomogeneity can suppress oscillations, changing the droplet’s shape. In a definite region of parameters, the two-dimensional spatial modulation can lead to the excitation of periodic oscillations. The influence of the Biot number on the shape of the droplets is studied.
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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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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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Rho, Hoon Suk, i Han Gardeniers. "Microfluidic Droplet-Storage Array". Micromachines 11, nr 6 (23.06.2020): 608. http://dx.doi.org/10.3390/mi11060608.
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A microfluidic droplet-storage array that is capable of the continuous operation of droplet formation, storing, repositioning, retrieving, injecting and restoring is demonstrated. The microfluidic chip comprised four valve-assisted droplet generators and a 3 × 16 droplet-storage array. The integrated pneumatically actuated microvalves enable the precise control of aqueous phase dispensing, as well as carrier fluid flow path and direction for flexible manipulating water-in-oil droplets in the chip. The size of droplets formed by the valve-assisted droplet generators was validated under various operating conditions such as pressures for introducing solutions and dispensing time. In addition, flexible droplet addressing in the storage array was demonstrated by storing droplets with various numbers and compositions in different storage units as well as rearranging their stored positions. Moreover, serial injections of new droplets into a retrieved droplet from a storage unit was performed to show the potential of the platform in sequential dosing on incubated droplet-based reactors at the desired timeline. The droplet-storage array with great freedom and flexibility in droplet handling could be applied for performing complex chemical and biologic reactions, especially in which incubation and dosing steps are necessary.
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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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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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Leng, Yupeng, Chengming He, Qian Wang, Zhixia He, Nigel Simms i Peng Zhang. "Symmetry-Breaking-Induced Internal Mixing Enhancement of Droplet Collision". Symmetry 16, nr 1 (29.12.2023): 47. http://dx.doi.org/10.3390/sym16010047.
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Binary droplet collision is a basic fluid phenomenon for many spray processes in nature and industry involving lots of discrete droplets. It exists an inherent mirror symmetry between two colliding droplets. For specific cases of the collision between two identical droplets, the head-on collision and the off-center collision, respectively, show the axisymmetric and rotational symmetry characteristics, which is useful for the simplification of droplet collision modeling. However, for more general cases of the collision between two droplets involving the disparities of size ratio, surface tension, viscosity, and self-spin motions, the axisymmetric and rotational symmetry droplet deformation and inner flow tend to be broken, leading to many distinct phenomena that cannot occur for the collision between two identical droplets owing to the mirror symmetry. This review focused on interpreting the asymmetric droplet deformation and the collision-induced internal mixing that was affected by those symmetry breaking factors, such as size ratio effects, Marangoni Effects, non-Newtonian effects, and droplet self-spin motion. It helps to understand the droplet internal mixing for hypergolic propellants in the rocket engineering and microscale droplet reactors in the biological engineering, and the modeling of droplet collision in real combustion spray processes.
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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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Dong, Jian, Siguang Lu, Bilong Liu, Jie Wu i Mengqi Chen. "Numerical Investigation of Heat Transfer and Development in Spherical Condensation Droplets". Micromachines 15, nr 5 (26.04.2024): 566. http://dx.doi.org/10.3390/mi15050566.
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This study establishes thermodynamic assumptions regarding the growth of condensation droplets and a mathematical formulation of droplet energy functionals. A model of the gas–liquid interface condensation rate based on kinetic theory is derived to clarify the relationship between condensation conditions and intermediate variables. The energy functional of a droplet, derived using the principle of least action, partially elucidates the inherent self-organizing growth laws of condensed droplets, enabling predictive modeling of the droplet’s growth. Considering the effects of the condensation environment and droplet heat transfer mechanisms on droplet growth dynamics, we divide the process into three distinct stages, marked by critical thresholds of 105 nm3 and 1010 nm3. Our model effectively explains why the observed contact angle fails to reach the expected Wenzel contact angle. This research presents a detailed analysis of the factors affecting surface condensation and heat transfer. The predictions of our model have an error rate of less than 3% error compared to baseline experiments. Consequently, these insights can significantly contribute to and improve the design of condensation heat transfer surfaces for the phase-change heat sinks in microprocessor chips.
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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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Airey, M. W., R. G. Harrison, K. L. Aplin, C. Pfrang i B. McGinness. "Electrical effects on droplet behaviour". Journal of Physics: Conference Series 2702, nr 1 (1.02.2024): 012015. http://dx.doi.org/10.1088/1742-6596/2702/1/012015.
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Abstract The effect of charge on water droplets modulates various aspects of their behaviour. These include the droplet stability, evaporation, and lifetime. Microphysical models have been developed such that a reasonably good understanding of these processes has been achieved. However, the specific effects of charge deserve further scrutiny as they are an intrinsic component of the factors controlling droplet characteristics. Describing the effects of these requires an understanding of the electrostatic pressure present in the droplet and its surface tension. One way to test these effects and assess droplet response to charge is to take an experimental approach to make observations directly. In this study, individual droplets are levitated in an acoustic wave to allow isolated measurements to be taken. The droplets are monitored using a CCD camera with a microscope objective lens. In some cases, with sufficient charge present, effects on droplet stability can be observed as Rayleigh explosions, where a sudden drop in mass is seen superimposed on the evaporation profile. These events also allow the charge on the droplet to be calculated, which is then compared with the droplet evaporation. Another factor that plays a part in droplet behaviour is droplet composition. Different substances have different surface tension, and this is explored by performing some experiments on sulphuric acid droplets. Theory predicts that the more highly charged a droplet is, the more resistant to evaporation it becomes. Experimental data collected during this study agrees with this, with more highly charged droplets observed to have slower evaporation rates. However, highly charged drops were also observed to periodically become unstable during evaporation and undergo Rayleigh explosions. Each instability of a highly charged drop removes mass, reducing the overall droplet lifetime regardless of the slower evaporation rate. The sulphuric acid droplets were observed to be much more resistant to evaporation and no Rayleigh instabilities were observed.
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Krueger, Steven K. "Technical note: Equilibrium droplet size distributions in a turbulent cloud chamber with uniform supersaturation". Atmospheric Chemistry and Physics 20, nr 13 (8.07.2020): 7895–909. http://dx.doi.org/10.5194/acp-20-7895-2020.
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Abstract. In a laboratory cloud chamber that is undergoing Rayleigh–Bénard convection, supersaturation is produced by isobaric mixing. When aerosols (cloud condensation nuclei) are injected into the chamber at a constant rate, and the rate of droplet activation is balanced by the rate of droplet loss, an equilibrium droplet size distribution (DSD) can be achieved. We derived analytic equilibrium DSDs and probability density functions (PDFs) of droplet radius and squared radius for conditions that could occur in such a turbulent cloud chamber when there is uniform supersaturation. We neglected the effects of droplet curvature and solute on the droplet growth rate. The loss rate due to fallout that we used assumes that (1) the droplets are well-mixed by turbulence, (2) when a droplet becomes sufficiently close to the lower boundary, the droplet's terminal velocity determines its probability of fallout per unit time, and (3) a droplet's terminal velocity follows Stokes' law (so it is proportional to its radius squared). Given the chamber height, the analytic PDF is determined by the mean supersaturation alone. From the expression for the PDF of the radius, we obtained analytic expressions for the first five moments of the radius, including moments for truncated DSDs. We used statistics from a set of measured DSDs to check for consistency with the analytic PDF. We found consistency between the theoretical and measured moments, but only when the truncation radius of the measured DSDs was taken into account. This consistency allows us to infer the mean supersaturations that would produce the measured PDFs in the absence of supersaturation fluctuations. We found that accounting for the truncation radius of the measured DSDs is particularly important when comparing the theoretical and measured relative dispersions of the droplet radius. We also included some additional quantities derived from the analytic DSD: droplet sedimentation flux, precipitation flux, and condensation rate.
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Rong, Feng, Li-min He, Yu-ling Lü, Ce Wang i Yi-shuo Han. "Dynamics Analysis of Droplets Collision with the Wall Driven by Buoyancy". Journal of Physics: Conference Series 2594, nr 1 (1.10.2023): 012045. http://dx.doi.org/10.1088/1742-6596/2594/1/012045.
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Abstract Dynamics analysis of the oil droplet in water impacting on a rigid wall in the range of Re=9.3 ∼ 231.39, We=0.003 ∼ 0.637 was carried out by combining microscopic experiment with theoretical study. In the oil droplet’s force equation, we consider the added mass force and the water film induced force, in addition to the conventional forces, i.e. buoyancy and resistance to flow. Stokes-Reynolds drainage equation (i.e. SR model) and Young-Laplace equation (i.e. YL model) are combined with the force equation to numerically solve the motion law of oil droplets near the wall for different control parameters. The study indicates that coupled model would expect oil droplet velocities, motion trajectories and capture the kinetic behaviors of the water-film drainage evolution. The interfacial deformation of oil droplets causes changes in the pressure and the pressure distribution pattern has an important relationship with the shape of the oil droplet interface. These two forces play a dominant role in droplet motion during the collision and the maximum value of these two forces increases with increasing droplet size and Re number. Future research should shift towards complex oil-water systems and consider the effects of chemicals on oil droplets so that the application of the model will be more generalisable. At the same time, computer technology should be used to transfer the two-dimensional view to a three-dimensional view to analyse the deformation of the oil-water interface and to better understand the drainage process of the water film.
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Zeng, Xiang Hui, Le Hua Qi, Hua Huang, Xiao Shan Jiang i Yuan Xiao. "Experimental Research of Pneumatic Drop-on-Demand High Temperature Droplet Deposition for Rapid Prototyping". Key Engineering Materials 419-420 (październik 2009): 405–8. http://dx.doi.org/10.4028/www.scientific.net/kem.419-420.405.
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Generating high-melting-point metals droplet is a bottleneck in the area of droplet-based rapid prototyping. In our research, a pneumatic drop-on-demand (DOD) generator was developed which can spray A2024 alloy successfully, and the maximum ejection temperature can reach to 1200°C. Experiments were conducted to examine the influence of the oxygen content on the metal droplet spray. The uniform A2024 droplet was ejected stably under the condition where the oxygen content was less than 25ppm. As the solenoid valve was opened once with different time span, four cases were observed: droplet stream, three droplets, two droplets and one single droplet. A2024 droplets were deposited continuously on top of each other in vertical direction to form vertical columns, which meant the graphite nozzle can be used in experiment. A simple square tube was produced by regulating the droplet generator, which showed the rapid prototyping by high-melting-point droplet deposition is feasible.
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Liang, Gaojie, Lijun Liu, Haiqian Zhao, Cong Li i Nandi Zhang. "Study on droplet nucleation position and jumping on structured hydrophobic surface using the lattice Boltzmann method". Thermal Science, nr 00 (2021): 149. http://dx.doi.org/10.2298/tsci201206149l.
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In this study, droplet nucleation and jumping on the conical microstructure surface is simulated using the Lattice Boltzmann Method (LBM). The nucleation and jumping laws of the droplet on the surface are summarized. The numerical results suggest that the height and the gap of the conical microstructure exhibit a significant influence on the nucleation position of the droplet. When the ratio of height to the gap of the microstructure(H/D) is small, the droplet tends to nucleate at the bottom of the structure. Otherwise, the droplet tends to nucleate towards the side of the structure. The droplet grown in the side nucleation mode possesses better hydrophobicity than that of the droplet grown in the bottom nucleation mode and the droplet jumping becomes easier. Apart from the coalescence of the droplets jumping out of the surface, jumping of individual droplets may also occur under certain conditions. The ratio of the clearance to the width of the conical microstructure(D/F) depends on the jumping mode of the droplet. The simulation results indicate that when the D/F ratio is greater than 1.2, the coalescence jump of droplets is likely to occur. On the contrary, the individual jump of droplets is easy to occur.
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Barkay, Zahava. "In Situ Imaging of Nano-Droplet Condensation and Coalescence on Thin Water Films". Microscopy and Microanalysis 20, nr 2 (28.11.2013): 317–22. http://dx.doi.org/10.1017/s1431927613013834.
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AbstractTwo related aspects of nano-droplet condensation and droplets coalescence are studied for droplets on self-supported thin water films. The experiments are conducted in the environmental scanning electron microscope using wet scanning transmission electron microscopy. Favorable condensation sites are examined and in-situ position-controlled condensation experiments are conducted. The interaction among condensed multi-droplets as well as between a single droplet and the underneath nano-thick water film are dynamically examined with 10nm lateral resolution. The droplet round shape is reshaped to flat-like facets in-between droplets of 30-230 nm separation. Dynamic imaging of a few minutes duration shows a delayed coalescence effect, being explained by increased droplet-droplet electrostatic interaction relative to van der Waals interaction.
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Yang, Xiaoyuan, Bingyao Huang, Yi Zhang i Yuyang Li. "Component Effects in Binary Droplet Impact Behaviors on the Heated Plate: Comparison Study of Ethanol/Propanol and Ethanol/Water Droplets and Observation of Novel Bubble Shrinkage Phenomenon". Applied Sciences 14, nr 11 (23.05.2024): 4459. http://dx.doi.org/10.3390/app14114459.
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This work aims to investigate the effect of liquid physical properties on the behavior of binary droplets impact on the heated smooth aluminum alloy plate with a high-speed imaging system. Two groups of mixed solutions with similar boiling point differences are selected as the working liquid, in which the low-boiling-point components are both ethanol and the high-boiling point components are propanol and water, respectively. Compared to the ethanol/propanol binary droplets, the experimental results show that the ethanol/water binary droplets have diverse impact phenomena and significantly broad transition boiling regimes, as well as the reduced droplet residence time and increased Leidenfrost temperature point. With the decreasing ethanol content in ethanol/water binary droplets, these effects become more prominent. For secondary atomization, the ethanol/water binary droplet undergoes parent droplet breakup into fragment droplets with larger diameters (Ds > 0.3 mm). Both binary droplets produce satellite droplets with small diameters (Ds < 0.3 mm) by puffing and ejection. In terms of the ethanol/propanol binary droplet impact, the probability of puffing is higher and the satellite droplet diameters are small. In the ethanol/water binary droplet impact, the probability of ejection is higher and the satellite droplet diameter distribution is wider. When an ethanol/water binary droplet of 25 vol.% ethanol content impacts the heated wall at Ts = 120 °C, a novel large bubble shrinkage phenomenon occurs at the late stage of droplet evaporation. This phenomenon is proposed to be relevant to the increasing surface tension and saturation temperature with decreasing ethanol content, as well as the decreasing ambient temperature above the top surface of the bubble.
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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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Xing, Lei, Jinyu Li, Minghu Jiang i Lixin Zhao. "Dynamic behavior of compound droplets with millimeter-sized particles impacting substrates with different wettabilities". Physics of Fluids 35, nr 2 (luty 2023): 022108. http://dx.doi.org/10.1063/5.0137505.
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The dynamic behavior of compound droplets, which are made up of a millimeter-sized particle and distilled water, impacting substrates of different wettabilities is investigated via high-speed photography. The effects of the size of the particle within the compound droplet, substrate contact angle, and impact height on the deformation of the droplets and the characteristics of the impact are analyzed. It is found that the collisions of compound droplets with substrates can be classified into four categories based on the observed experimental phenomena that occur during the impact. These categories are referred to as adhesion collision, rebound collision, daughter-droplet collision (or partial rebound collision), and breakup collision. We consider both the impact of water droplets and compound droplets (with one of two different-sized particles) on substrates of different wettabilities. The effects of inertia, surface tension, and adhesion between the substrate and the liquid droplet, and adhesion between the particle and the liquid droplet are considered to explain the different collision phenomena of compound droplets and reveal the evolution mechanism of the droplet morphologies in the experiments. Furthermore, the effects of the height from which the droplet is released and the contact angle of the substrate (i.e., its wettability) on the maximum spreading diameter and maximum jet height of the droplet are presented quantitatively. The effect of the size of the particle within the compound droplet and the substrate contact angle on the dynamic behavior of the compound droplet subject to impact with the substrate is also described.
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Nguyen, Khanh P., i Truong V. Vu. "Collision Modes of Two Eccentric Compound Droplets". Processes 8, nr 5 (18.05.2020): 602. http://dx.doi.org/10.3390/pr8050602.
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A compound droplet with its single inner droplet appears in a broad range of applications and has received much attention in recent years. However, the role of the inner droplet location on the dynamical behaviors of the compound droplet is still not completely understood. Accordingly, the present study numerically deals with the eccentricity of the compound droplet affecting its colliding behaviors with the other droplet in a simple shear flow. The solving method is a front-tracking technique that treats the droplet interface as connected elements moving on a rectangular fixed grid. Initially, two compound droplets assumed circular are placed at a distance symmetrically to the domain center and they come into contact, because of the shear flow, when time progresses. During the collision process, the inner droplet that is initially located at a distance to its outer droplet center circulates around this center. It is found that this rotation also contributes to the formation of the collision modes including the reversing, passing-over and merging ones. Starting from a passing-over mode, a transition to a reversing mode or a merging mode can appear when the inner droplets, in terms of their centroids, are closer than their outer droplets. However, the location of the inner droplet within the outer droplet only has an effect when the value of the Capillary number Ca is varied from 0.01 to 0.08. For Ca < 0.01 corresponding to the merging mode and Ca ≥ 0.16 corresponding to the passing-over mode, the inner droplet position has almost no impact on the collision behaviors of two compound droplets.
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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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Mudugamuwa, Amith, Samith Hettiarachchi, Gehan Melroy, Shanuka Dodampegama, Menaka Konara, Uditha Roshan, Ranjith Amarasinghe, Dumith Jayathilaka i Peihong Wang. "Vision-Based Performance Analysis of an Active Microfluidic Droplet Generation System Using Droplet Images". Sensors 22, nr 18 (13.09.2022): 6900. http://dx.doi.org/10.3390/s22186900.
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This paper discusses an active droplet generation system, and the presented droplet generator successfully performs droplet generation using two fluid phases: continuous phase fluid and dispersed phase fluid. The performance of an active droplet generation system is analysed based on the droplet morphology using vision sensing and digital image processing. The proposed system in the study includes a droplet generator, camera module with image pre-processing and identification algorithm, and controller and control algorithm with a workstation computer. The overall system is able to control, sense, and analyse the generation of droplets. The main controller consists of a microcontroller, motor controller, voltage regulator, and power supply. Among the morphological features of droplets, the diameter is extracted from the images to observe the system performance. The MATLAB-based image processing algorithm consists of image acquisition, image enhancement, droplet identification, feature extraction, and analysis. RGB band filtering, thresholding, and opening are used in image pre-processing. After the image enhancement, droplet identification is performed by tracing the boundary of the droplets. The average droplet diameter varied from ~3.05 mm to ~4.04 mm in the experiments, and the average droplet diameter decrement presented a relationship of a second-order polynomial with the droplet generation time.
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Marlina, Ena, Akhmad Faruq Alhikami, Metty Trisna Negara, Sekar Rahima Sahwahita i Mochammad Basjir. "Characterization of Voltage Generation Obtained from Water Droplets on a Taro Leaf (Colocasia esculenta L) Surface". Journal of Earth Energy Engineering 12, nr 2 (31.10.2023): 50–57. http://dx.doi.org/10.25299/jeee.2023.12916.
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Voltage generation was obtained using a water droplet characterization on a taro (Colocasia esculenta L) leaf surface. This method relies on the superhydrophobic effect from the contact angle between the water droplet and the taro leaf’s surface allowing electron jumping and voltage generation. Water droplets were dropped on the top of taro leaf surface equipped with aluminum foil underneath as an electrode. The voltage was measured at various slope angles of 20°, 40° and 60° in a real-time basis. A digital camera was used to capture the droplet movement and characterization. It is found that the taro leaf has a surface morphology of nano-sized pointed pillars which created a superhydrophobic field. The energy generation was primarily obtained from the electron jump which was caused by the surface tension of the nano-stalagmite structure assisted by the minerals contained in the taro leaf surface. The results reported that the smaller the droplet radius (the smaller the droplet surface area), the greater the droplet surface tension and the greater the voltage generation. Furthermore, the highest voltage generation was obtained 321.2 mV at 20°-degree angle of slopes.
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Zeng, Wen, Dong Xiang i Hai Fu. "Prediction of Droplet Production Speed by Measuring the Droplet Spacing Fluctuations in a Flow-Focusing Microdroplet Generator". Micromachines 10, nr 12 (25.11.2019): 812. http://dx.doi.org/10.3390/mi10120812.
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In a flow-focusing microdroplet generator, by changing the flow rates of the two immiscible fluids, production speed can be increased from tens to thousands of droplets per second. However, because of the nonlinearity of the flow-focusing microdroplet generator, the production speed of droplets is difficult to quantitatively study for the typical flow-focusing geometry. In this paper, we demonstrate an efficient method that can precisely predict the droplet production speed for a wide range of fluid flow rates. While monodisperse droplets are formed in the flow-focusing microchannel, droplet spacing as a function of time was measured experimentally. We discovered that droplet spacing changes periodically with time during each process of droplet generation. By comparing the frequency of droplet spacing fluctuations with the droplet production speed, precise predictions of droplet production speed can be obtained for different flow conditions in the flow-focusing microdroplet generator.