Journal articles on the topic 'Volume-surface diameter of droplets'
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1
Trapuzzano, Matthew, Andrés Tejada-Martínez, Rasim Guldiken, and Nathan Crane. "Volume and Frequency-Independent Spreading of Droplets Driven by Ultrasonic Surface Vibration." Fluids 5, no. 1 (February 2, 2020): 18. http://dx.doi.org/10.3390/fluids5010018.
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Many industrial processes depend on the wetting of liquids on various surfaces. Understanding the wetting effects due to ultrasonic vibration could provide a means for changing the behavior of liquids on any surface. In previous studies, low-frequency surface vibrations have been used to alter wetting states of droplets by exciting droplet volume modes. While high-frequency (>20 kHz) surface vibration can also cause droplets to wet or spread on a surface, this effect is relatively uncharacterized. In this study, droplets of various liquids with volumes ranging from 2 to 70 µL were vibrated on hydrophobic-coated (FluoroSyl) glass substrates fixed to a piezoelectric transducer at varying amplitudes and at a range of frequencies between 21 and 42 kHz. The conditions for contact line motion were evaluated, and the change in droplet diameter under vibration was measured. Droplets of all tested liquids initially begin to spread out at a similar surface acceleration level. The results show that the increase in diameter is proportional to the maximum acceleration of the surface. Finally, liquid properties and surface roughness may also produce some secondary effects, but droplet volume and excitation frequency do not significantly change the droplet spreading behavior within the parameter range studied.
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Wang, Yiting, Lijuan Qian, Zhongli Chen, and 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, no. 9 (September 9, 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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Huang, Xuefeng, Ling Sheng, Yibin Lu, and Shengji Li. "Atomization Characteristics of Hydrogen Peroxide Solutions in Electrostatic Field." Micromachines 13, no. 5 (May 13, 2022): 771. http://dx.doi.org/10.3390/mi13050771.
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Hydrogen peroxide (H2O2) can be considered as a sterilant or a green propellant. For a common use in industrial application, spray is an effective method to form fine H2O2 droplets. In this paper, electrostatic atomization based on the configuration of needle ring electrodes is proposed to produce H2O2 spray by minimizing its effective surface tension. The breakup performances of H2O2 ligaments can be improved by increasing the electric field intensity, reducing the nozzle size, and adjusting suitable volume flow rate. The smallest average diameter of breakup droplets for 35 wt. % concentration H2O2 solution reached 92.8 μm under optimum operation conditions. The H2O2 concentration significantly influenced the breakup performance owing to the concentration effect on comprehensive physical properties such as density, surface tension, viscosity, and permittivity. The average diameters of breakup droplets decreased with decreasing H2O2 concentration. At 8 wt. % concentration, the average breakup droplet diameter was reduced to 67.4 μm. Finally, electrostatic atomization mechanism of H2O2 solution was analyzed by calculating dimensionless parameters of Re, We, and Oh numbers with the combination of the operation conditions and physical properties for in-depth understanding the breakup behaviors. The calculation showed that the minimum average diameter of breakup droplets was obtained at 8 wt. % concentration at the investigated range of H2O2 concentration, which kept in agreement with the experimental results.
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Batalov, V. G., R. A. Stepanov, and A. U. Vasilev. "Quality estimation of the nozzle spray by measuring the brightness of the reflected light." Journal of Physics: Conference Series 2057, no. 1 (October 1, 2021): 012083. http://dx.doi.org/10.1088/1742-6596/2057/1/012083.
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Abstract This paper presents the results of the laboratory and numerical experiments performed to measure the sizes of transparent liquid droplets sprayed in air. The results of the laboratory experiments were mainly obtained using the Glare Point Technique (GPT) which gave information about the droplet size and the brightness of the light reflected by drops. The relationship between the brightness of the light reflected from the surface of droplets and their sizes was analyzed. Theoretically, the brightness of light scattered by a single spherical drop is proportional to the drop surface area and, accordingly, to the square of the drop diameter. It has been observed experimentally and verified numerically that the theoretical dependence obtained is relevant only for the brightest droplets because of nonuniform illumination. The results of the numerical experiments with a random sample of drops indicated the dependence of the total brightness of reflected light on the effective droplet size. It is shown that, for a fixed total volume, the total brightness of light reflected by drops is proportional to the droplet Sauter mean diameter.
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Clément, Sophie, Catherine Fauvelle, Emilie Branche, Vincent Kaddai, Stéphanie Conzelmann, Tujana Boldanova, Birke Bartosch, Kaori Minehira, and Francesco Negro. "Role of seipin in lipid droplet morphology and hepatitis C virus life cycle." Journal of General Virology 94, no. 10 (October 1, 2013): 2208–14. http://dx.doi.org/10.1099/vir.0.054593-0.
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Infectious hepatitis C virus (HCV) particle assembly starts at the surface of lipid droplets, cytoplasmic organelles responsible for neutral fat storage. We analysed the relationship between HCV and seipin, a protein involved in lipid droplet maturation. Although seipin overexpression did not affect the total mean volume occupied by lipid droplets nor the total triglyceride and cholesterol ester levels per cell, it caused an increase in the mean diameter of lipid droplets by 60 %, while decreasing their total number per cell. The latter two effects combined resulted in a 34 % reduction of the total outer surface area of lipid droplets per cell, with a proportional decrease in infectious viral particle production, probably due to a defect in particle assembly. These results suggest that the available outer surface of lipid droplets is a critical factor for HCV release, independent of the neutral lipid content of the cell.
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Li, Ze Fu, Lin Zhang, Xuan Luo, Xiao Jun Wang, and Yi Yang. "Simulation of Droplets Formation in Co-Flowing Microfluidic Channels." Applied Mechanics and Materials 513-517 (February 2014): 4180–84. http://dx.doi.org/10.4028/www.scientific.net/amm.513-517.4180.
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Emulsion droplets or multi-emulsion droplet formation was important for functional materials synthesizing by microfluidic. To obtain tunable monodisperse droplets with millimeter scale, the flow regime in co-flowing channels was divided by numerical simulation. A typical co-flowing model was created using finite volume method, and the VOF (volume of fluid) muti-phase model was selected. Then, droplets were produced by changing the velocity ratio under the dripping regime. Compared to the experimental value of droplet diameter, theoretical and numerical absolute error was below 60 % and 15 %, separately. Greet agreement of diameter changing tendency was found in simulation and experiment.
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Gao, Sihang, Fuqiang Chu, Xuan Zhang, and Xiaomin Wu. "Behavior of condensed droplets growth and jumping on superhydrophobic surface." E3S Web of Conferences 128 (2019): 07003. http://dx.doi.org/10.1051/e3sconf/201912807003.
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Droplets on the superhydrophobic surface can fall off the surface spontaneously, which greatly promote dropwise condensation. This study considers a continuous droplet condensation process including droplet growth and droplet jumping. A droplet growth model considered NCG is developed and droplet jumping is simulated using VOF (Volume Of Fluid) model. Al–based superhydrophobic surfaces are prepared using chemical deposition and etching method. The Al-based superhydrophobic surface has a contact angle of 157°±1° and a rolling angle of 2°±1°. An observation experiment is designed to observe droplet jumping on superhydrophobic surface using a high– speed camera system. The result of droplet growth model shows a good match with experimental data in mid-term of droplet growth. Fordroplet jumping, simulation and experiment results show that droplet jumping of different diameter hasa universality in a non–dimensional form. The jumping process can be divided into 3 stages and droplet vibration is observed.
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OLIVEIRA, RONE B. DE, ULISSES R. ANTUNIASSI, and MARCO A. GANDOLFO. "Spray adjuvant characteristics affecting agricultural spraying drift." Engenharia Agrícola 35, no. 1 (February 2015): 109–16. http://dx.doi.org/10.1590/1809-4430-eng.agric.v35n1p109-116/2015.
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This study defined the main adjuvant characteristics that may influence or help to understand drift formation process in the agricultural spraying. It was evaluated 33 aqueous solutions from combinations of various adjuvants and concentrations. Then, drifting was quantified by means of wind tunnel; and variables such as percentage of droplets smaller than 50 μm (V50), 100 μm (V100), diameter of mean volume (DMV), droplet diameter composing 10% of the sprayed volume (DV0.1), viscosity, density and surface tension. Assays were performed in triplicate, using Teejet XR8003 flat fan nozzles at 200 kPa (medium size droplets). Spray solutions were stained with Brilliant Blue Dye at 0.6% (m/ v). DMV, V100, viscosity cause most influence on drift hazardous. Adjuvant characteristics and respective methods of evaluation have applicability in drift risk by agricultural spray adjuvants.
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Yao, S. C., L. E. Hochreiter, and K. Y. Cai. "Dynamics of Droplets Impacting on Thin Heated Strips." Journal of Heat Transfer 110, no. 1 (February 1, 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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Egley, Grant H., James E. Hanks, and C. Douglas Boyette. "Invert Emulsion Droplet Size and Mycoherbicidal Activity ofColletotrichum truncatum." Weed Technology 7, no. 2 (June 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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Zhong, Yuan, Haicun Du, Ying Zhang, Yue Chen, Qiang Liu, and Jie Huang. "Experimental research on dynamic characteristics of viscous droplets impacting rough solid surfaces at different temperatures." Canadian Journal of Physics 97, no. 12 (December 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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Chaim, Aldemir, Maria Conceição Peres Young Pessoa, João Camargo Neto, and Luiz Carlos Hermes. "Comparison of microscopic method and computational program for pesticide deposition evaluation of spraying." Pesquisa Agropecuária Brasileira 37, no. 4 (April 2002): 493–96. http://dx.doi.org/10.1590/s0100-204x2002000400010.
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The main objective of this work was to compare two methods to estimate the deposition of pesticide applied by aerial spraying. Hundred and fifty pieces of water sensitive paper were distributed over an area of 50 m length by 75 m width for sampling droplets sprayed by an aircraft calibrated to apply a spray volume of 32 L/ha. The samples were analysed by visual microscopic method using NG 2 Porton graticule and by an image analyser computer program. The results reached by visual microscopic method were the following: volume median diameter, 398±62 mum; number median diameter, 159±22 mum; droplet density, 22.5±7.0 droplets/cm² and estimated deposited volume, 22.2±9.4 L/ha. The respective ones reached with the computer program were: 402±58 mum, 161±32 mum, 21.9±7.5 droplets/cm² and 21.9±9.2 L/ha. Graphs of the spatial distribution of droplet density and deposited spray volume on the area were produced by the computer program.
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Mimouni, S., N. Mechitoua, A. Foissac, M. Hassanaly, and M. Ouraou. "CFD Modeling of Wall Steam Condensation: Two-Phase Flow Approach versus Homogeneous Flow Approach." Science and Technology of Nuclear Installations 2011 (2011): 1–10. http://dx.doi.org/10.1155/2011/941239.
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The present work is focused on the condensation heat transfer that plays a dominant role in many accident scenarios postulated to occur in the containment of nuclear reactors. The study compares a general multiphase approach implemented in NEPTUNE_CFD with a homogeneous model, of widespread use for engineering studies, implemented inCode_Saturne. The model implemented in NEPTUNE_CFD assumes that liquid droplets form along the wall within nucleation sites. Vapor condensation on droplets makes them grow. Once the droplet diameter reaches a critical value, gravitational forces compensate surface tension force and then droplets slide over the wall and form a liquid film. This approach allows taking into account simultaneously the mechanical drift between the droplet and the gas, the heat and mass transfer on droplets in the core of the flow and the condensation/evaporation phenomena on the walls. As concern the homogeneous approach, the motion of the liquid film due to the gravitational forces is neglected, as well as the volume occupied by the liquid. Both condensation models and compressible procedures are validated and compared to experimental data provided by the TOSQAN ISP47 experiment (IRSN Saclay). Computational results compare favorably with experimental data, particularly for the Helium and steam volume fractions.
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Batishcheva, KSENIA A., and ATLANT E. Nurpeiis. "WATER DROPLET EVAPORATION IN A CHAMBER ISOLATED FROM THE EXTERNAL ENVIRONMENT." Tyumen State University Herald. Physical and Mathematical Modeling. Oil, Gas, Energy 6, no. 3 (2020): 8–22. http://dx.doi.org/10.21684/2411-7978-2020-6-3-8-22.
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With an increase in the productivity of power equipment and the miniaturization of its components, the use of traditional thermal management systems becomes insufficient. There is a need to develop drip heat removal systems, based on phase transition effects. Cooling with small volumes of liquids is a promising technology for microfluidic devices or evaporation chambers, which are self-regulating systems isolated from the external environment. However, the heat removal during evaporation of droplets into a limited volume is a difficult task due to the temperature difference in the cooling device and the concentration of water vapor that is unsteady in time depending on the mass of the evaporated liquid. This paper presents the results of an experimental study of the distilled water microdrops’ (5-25 μl) evaporation on an aluminum alloy AMg6 with the temperatures of 298-353 K in an isolated chamber (70 × 70 × 30 mm3) in the presence of heat supply to its lower part. Based on the analysis of shadow images, the changes in the geometric dimensions of evaporating drops were established. They included the increase in the contact diameter, engagement of the contact line due to nano roughening and chemical composition inhomogeneous on the surface (90-95% of the total evaporation time) of the alloy and a decrease in the contact diameter. The surface temperature and droplet volume did not affect the sequence of changes in the geometric dimensions of the droplets. It was found that the droplet volume has a significant effect on the evaporation time at relatively low substrate temperatures. The results of the analysis of droplet evaporation rates and hygrometer readings have shown that reservoirs with salt solutions can be used in isolated chambers to control the concentration of water vapor. The water droplets evaporation time was determined. The analysis of the time dependences of the evaporation rate has revealed that upon the evaporation of droplets in an isolated chamber under the conditions of the present experiment, the air was not saturated with water vapor. The latter did not affect the evaporation rate.
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Chandra, S., and S. D. Aziz. "Leidenfrost Evaporation of Liquid Nitrogen Droplets." Journal of Heat Transfer 116, no. 4 (November 1, 1994): 999–1006. http://dx.doi.org/10.1115/1.2911477.
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The evaporation of a single droplet of liquid nitrogen, levitated during film boiling above a solid, impervious surface, was studied experimentally. The droplet initial diameter (1.9 mm), surface temperature (~20°C), ambient temperature (~20°C), and ambient pressure (~0.1 MPa) were held constant. The principal parameters varied were the surface material (copper or glass), and roughness (0.35 to 50 μm). Measurements were made of the droplet diameter evolution and the surface temperature variation during droplet impact. Predictions from existing models of droplets in Leidenfrost evaporation agree well with measurements of the droplet evaporation rate. The droplet lifetime was found to be slightly longer on the glass surface than it was on the copper surface, corresponding to the greater cooling of the glass surface during droplet impact. The droplet evaporation rate was unchanged by small increases in surface roughness. However, ridges on the surface with a height of the same magnitude as the thickness of the vapor film under the drop caused vapor bubble nucleation in the droplet, and significantly reduced the droplet evaporation time.
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Vitkovicova, Rut, and Pavol Vitkovic. "Control of droplet size in rain-zone in wet cooling tower." EPJ Web of Conferences 180 (2018): 02119. http://dx.doi.org/10.1051/epjconf/201818002119.
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The performance of the wet cooling tower is significantly affected by the droplet size occurring in the rain zone. In order to effectively manage the size of these droplets, it was necessary to experimentally determine the effect of the fills of the cooling towers on droplets. Five types of cooling fillers were used for experimental measurements: 3 film fills and 2 splash fills - trickle and grid. Drop size measurements were performed using the LIF method. Histograms of droplets size were obtained from measured droplet sizes under each fill, and for each fill, the Sauter droplet diameter was then calculated. According to a theoretical analysis of a breakdown of droplets, the combinations of some fills and the effect of their surface treatment on the droplet diameter were then measured for comparison.
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Faber, Spencer, Jeffrey R. French, and Robert Jackson. "Laboratory and in-flight evaluation of measurement uncertainties from a commercial Cloud Droplet Probe (CDP)." Atmospheric Measurement Techniques 11, no. 6 (June 25, 2018): 3645–59. http://dx.doi.org/10.5194/amt-11-3645-2018.
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Abstract. Laboratory and in-flight evaluations of uncertainties of measurements from a Cloud Droplet Probe (CDP) are presented. A description of a water-droplet-generating device, similar to those used in previous studies, is provided along with validation of droplet sizing and positioning. Seven experiments with droplet diameters of 9, 17, 24, 29, 34, 38, and 46 µm tested sizing and counting performance across a 10 µm resolution grid throughout the sample area of a CDP. Results indicate errors in sizing that depend on both droplet diameter and position within the sample area through which a droplet transited. The CDP undersized 9µm droplets by 1–4 µm. Droplets with diameters of 17 and 24 µm were sized to within 2 µm, which is the nominal CDP bin width for droplets of that size. The majority of droplets larger than 17 µm were oversized by 2–4 µm, while a small percentage were severely undersized, by as much as 30 µm. This combination led to an artificial broadening and skewing of the spectra such that mean diameters from a near-monodisperse distribution compared well (within a few percent), while the median diameters were oversized by 5–15 %. This has implications on how users should calibrate their probes. Errors in higher-order moments were generally less than 10 %. Comparisons of liquid water content (LWC) calculated from the CDP and that measured from a Nevzorov hot-wire probe were conducted for 17 917 1 Hz in-cloud points. Although some differences were noted based on volume-weighted mean diameter and total droplet concentration, the CDP-estimated LWC exceeded that measured by the Nevzorov by approximately 20 %, more than twice the expected difference based on results of the laboratory tests and considerations of Nevzorov collection efficiency.
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Thakur, Neha, and Hari Murthy. "Simulation study of droplet formation in inkjet printing using ANSYS FLUENT." Journal of Physics: Conference Series 2161, no. 1 (January 1, 2022): 012026. http://dx.doi.org/10.1088/1742-6596/2161/1/012026.
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Abstract Flow simulations of jetting of inkjet drops are presented for water and ethylene glycol. In the inkjet printing process, droplet jetting behaviour is the deciding parameter for print quality. The multiphase volume of fluid (VOF) method is used because the interaction between two phases (air and liquid) is involved in the drop formation process. The commercial inkjet printer has a nozzle diameter of ∼73.2μm. In this work, a simulation model of inkjet printer nozzles with different diameters 40μm, 60μm, and 80μm are developed using ANSYS FLUENT software. It is observed that when water is taken as solvent then the stable droplets are generated at 60μm nozzle diameter till 9μs because of its low viscosity. For higher diameter, the stamen formation is observed. Ethylene glycol stable droplets are achieved at 80μm nozzle diameter till 9μs because of their high viscosity (∼10 times that of water). Along with the droplet formation, the sustainability of the droplet in the air before reaching the substrate is also important. The simulation model is an inexpensive, fast, and flexible alternative to study the ink characteristics of the real-world system without wasting resources.
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Gawel, Dorota, and Jan Zawala. "Automatic Single Droplet Generator with Control over Droplet Size and Detachment Frequency." Colloids and Interfaces 3, no. 3 (August 22, 2019): 57. http://dx.doi.org/10.3390/colloids3030057.
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This paper presents a quite simple, fully automatized single droplet generator, which can be an alternative for more expensive and complicated microfluidic devices. The simple generation nozzle connected to the pressure cells and cheap peristaltic pumps, synchronized via developed software with simple GUI (graphical user interface) implemented into the Raspberry Pi microcomputer allows precise control over the single droplet diameter and detachment frequency. The generator allows the formation of droplets of quite wide range of diameters without the need of orifice diameter replacements. Free control over time available for adsorption of surface active-substances over the surface of immobilized droplet, before its detachment from the orifice, is an advantage of the developed device.
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Ikezawa, Satoshi, Muneaki Wakamatsu, Joanna Pawłat, and Toshitsugu Ueda. "Control of a Micro-Droplet for Laser-Induced Breakdown Spectroscopy Solution Measurement." Solid State Phenomena 147-149 (January 2009): 639–44. http://dx.doi.org/10.4028/www.scientific.net/ssp.147-149.639.
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In this paper, laser-induced breakdown spectroscopy (LIBS) using micro-droplet NaCl solution and set-up for control of micro-droplets are described. Micro-droplets controlling technique is important for solution quantitative analysis. In this study, micro-droplet ejection system for sampling is designed and presented. This micro-droplet ejection system enable a constant volume of the sample liquid to be obtained and it takes advantage of the liquid physical state; the density of the solution can be controlled accurately. The method presented here generates small droplets (diameter 30 μm) by confining the entire volume of the sample material in the laser beam spot area (minimum beam spot diameter: 53.2 μm) and separating it from its surroundings. Using this liquid micronizing method, improved sensitivities are obtained. The Advantage of LIBS is a useful method for determining the elemental composition of various materials regardless of their physical state (solid, liquid, or gas) and without any preprocessing; it is a type of atomic emission spectroscopy (AES). Despite the advantage of qualitative analysis, quantitative analysis is difficult because of sample and plasma fluctuations. Generating constant volume of micro-size sample and proper sample control technique contribute to LIBS quantitative analysis.
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Ge, MaoSheng, Pute Wu, Delan Zhu, and Daniel P. Ames. "Comparison between sprinkler irrigation and natural rainfall based on droplet diameter." Spanish Journal of Agricultural Research 14, no. 1 (March 2, 2016): e1201. http://dx.doi.org/10.5424/sjar/2016141-8076.
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<p>An indoor experiment was conducted to analyze the movement characteristics of different sized droplets and their influence on water application rate distribution and kinetic energy distribution. Radial droplets emitted from a Nelson D3000 sprinkler nozzle under 66.3, 84.8, and 103.3 kPa were measured in terms of droplet velocity, landing angle, and droplet kinetic energy and results were compared to natural rainfall characteristics. Results indicate that sprinkler irrigation droplet landing velocity for all sizes of droplets is not related to nozzle pressure and the values of landing velocity are very close to that of natural rainfall. The velocity horizontal component increases with radial distance while the velocity vertical component decreases with radial distance. Additionally, landing angle of all droplet sizes decreases with radial distance. The kinetic energy is decomposed into vertical component and horizontal component due to the oblique angles of droplet impact on the surface soil, and this may aggravate soil erosion. Therefore the actual oblique angle of impact should be considered in actual field conditions and measures should be taken for remediation of soil erosion if necessary.</p>
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Mohammadi, Morteza, Sara Moghtadernejad, Percival J. Graham, and Ali Dolatabadi. "Dynamic Impact Behavior of Water Droplet on a Superhydrophobic Surface in the Presence of Stagnation Flow." Applied Mechanics and Materials 232 (November 2012): 267–72. http://dx.doi.org/10.4028/www.scientific.net/amm.232.267.
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The following study investigates splashing of impinging water droplets on superhydrophobic surfaces with and without the presence of a stagnation flow. Droplets were accelerated by either gravity or gravity and co-flow. By changing the height and the air flow velocity different combinations of stagnation flow and droplet velocity were created. The spreading diameter, spreading velocity and contact time were studied for different air and droplet speeds. It was clearly observed that for a fixed impact velocity (i.e. constant Weber number), the presence of the stagnation flow promotes splashing and formation of satellite droplets. Consequently, for the co-flow droplet impact experiments, the mass of the recoiled droplet is significantly smaller than that of the impinging droplet in still air.
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KIM, SEOL HA, JUN YOUNG KANG, HO SEON AHN, HANG JIN JO, and MOO HWAN KIM. "STUDY OF LEIDENFROST MECHANISM IN DROPLET IMPACTING ON HYDROPHILIC AND HYDROPHOBIC SURFACES." International Journal of Air-Conditioning and Refrigeration 21, no. 04 (December 2013): 1350028. http://dx.doi.org/10.1142/s2010132513500284.
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Water droplets, 2 mm in diameter, were allowed to fall freely onto hydrophobic and hydrophilic heated surfaces, and their impacts were imaged using high-speed cameras to investigate the droplet dynamics and heat transfer. As the heating power increased, the water droplets evaporated faster, eventually hovering over the surface due to the formation of a boiling film when the Leidenfrost point (LFP) was reached. The heat transfer from the surface into the droplet was evaluated, and LFP transition phenomena were investigated using time-resolved imaging of both side and bottom views. The hydrophilic surface showed a higher heat transfer rate and a higher LFP than the hydrophobic surface did. Furthermore, the droplet dynamics revealed very different shapes depending on the surface wettability; vigorous bubble nucleation and growth was observable for the hydrophilic surface, but not the hydrophobic surface. The rebound behavior of the droplets was analyzed based on the droplet free energy, including kinetic, potential, and surface energy terms.
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Pietsch, Renee B., Hinrich Grothe, Regina Hanlon, Craig W. Powers, Sunghwan Jung, Shane D. Ross, and David G. Schmale III. "Wind-driven spume droplet production and the transport ofPseudomonas syringaefrom aquatic environments." PeerJ 6 (September 26, 2018): e5663. http://dx.doi.org/10.7717/peerj.5663.
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Natural aquatic environments such as oceans, lakes, and rivers are home to a tremendous diversity of microorganisms. Some may cross the air-water interface within droplets and become airborne, with the potential to impact the Earth’s radiation budget, precipitation processes, and spread of disease. Larger droplets are likely to return to the water or adjacent land, but smaller droplets may be suspended in the atmosphere for transport over long distances. Here, we report on a series of controlled laboratory experiments to quantify wind-driven droplet production from a freshwater source for low wind speeds. The rate of droplet production increased quadratically with wind speed above a critical value (10-m equivalent 5.7 m/s) where droplet production initiated. Droplet diameter and ejection speeds were fit by a gamma distribution. The droplet mass flux and momentum flux increased with wind speed. Two mechanisms of droplet production, bubble bursting and fragmentation, yielded different distributions for diameter, speed, and angle. At a wind speed of about 3.5 m/s, aqueous suspensions of the ice-nucleating bacteriumPseudomonas syringaewere collected at rates of 283 cells m−2 s−1at 5 cm above the water surface, and at 14 cells m−2 s−1at 10 cm above the water surface. At a wind speed of about 4.0 m/s, aqueous suspensions ofP. syringaewere collected at rates of 509 cells m−2 s−1at 5 cm above the water surface, and at 81 cells m−2 s−1at 10 cm above the water surface. The potential for microbial flux into the atmosphere from aquatic environments was calculated using known concentrations of bacteria in natural freshwater systems. Up to 3.1 × 104 cells m−2 s−1of water surface were estimated to leave the water in potentially suspended droplets (diameters <100 µm). Understanding the sources and mechanisms for bacteria to aerosolize from freshwater aquatic sources may aid in designing management strategies for pathogenic bacteria, and could shed light on how bacteria are involved in mesoscale atmospheric processes.
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Widyatama, Arif, Akmal Irfan Majid, Teguh Wibowo, Deendarlianto Deendarlianto, and Samsul Kamal. "EXPERIMENTAL STUDY ON THE PHENOMENA ON THE SUCCESSIVE DROPLETS IMPACTING HOT COPPER SURFAC." Jurnal Penelitian Saintek 24, no. 2 (October 29, 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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Yu, Shangzhi, Qinglong Xie, Xiaoning Mao, Ying Duan, and Yong Nie. "Heat transfer in a novel microwave heating device coupled with atomization feeding." Thermal Science 26, no. 2 Part A (2022): 1185–95. http://dx.doi.org/10.2298/tsci210518288y.
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The heat transfer characteristics of the microwave heating coupled with atomization feeding were investigated using ethanol as the spray medium on a pressure swirl nozzle. The effects of spray height, flow rate and temperature on the sauter mean diameter of atomized droplets were examined. The results showed that the droplet sauter mean diameter was 12-130 ?m, which increased with the spray height and decreased with the flow rate and temperature of spray medium. Through the fitting of the experimental data, the dimensionless correlation of the droplet sauter mean diameter which was based on orifice diameter, Reynolds and Ohnesorge numbers was obtained. The calculated results were basically consistent with the experimental data within 15% error. The heat transfer characteristics of atomized droplets on high temperature surface of SiC bed heated by microwave were then investigated. The effects of spray flow rate, spray height, and spray temperature on the heat transfer characteristics were examined. The power of spray heat transfer decreased with the temperature and increased with the spray flow rate and spray height. The dimensionless correlation to describe the heat transfer characteristics of atomized droplets on the high temperature SiC surface under the microwave heating was obtained which included thermophysical properties of spray medium, spray parameters, and temperatures of the high temperature bed surface and spray medium, with the error of ?20%. These correlations can be used to predict the sauter mean diameter of the atomized droplets and the power of spray heat transfer in the microwave heating process.
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Markov, G. V., A. T. Volochko, V. G. Zaleski, and N. Yu Melnik. "Correlation of radius of cathode spot of vacuum arc of metals on the size of generated droplets." Proceedings of the National Academy of Sciences of Belarus, Physical-Technical Series 66, no. 4 (December 26, 2021): 391–98. http://dx.doi.org/10.29235/1561-8358-2021-66-4-391-398.
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The simple relation to estimate the cathode spot radius of a vacuum arc of pure metals is obtained. On its basis, is established between the cathode spot radius and the size of droplets generated by the cathode spot a correlation. This enables to find ways to reduce droplets in the plasma flow, which forms coatings by the vacuum electric arc method. The paper presents the results of experimental study of the droplet sizes depending on the vacuum arc current iд. The size and amount of the droplets on an area of 1 mm2 of the coating surface are determined using the ImageSP program. As the initial data, the microstructures of the coatings are used with an increase of: ç100, ç200, ç500, ç1000, ç1500. The droplets have been generated by a cathode spot of a vacuum arc for the alloy of the composition, at.%: 68Al–8Cr–4Nb–20Si. It is established that the number of droplets with a diameter of < 2 μm is generated most of all, and the number of droplets with a diameter > 10 μm is generated least of all. The number of generated droplets with a diameter from 2 to 10 μm slightly depends on the arc current iд. It is noted that the diameter of the alloy droplet is smaller than the diameter of the droplets generated by the cathode spot on its components due to the fact that the radius of the cathode spot on the alloy is smaller than the radius of the cathode spot on its pure components.
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Yang, A.-S., M.-T. Yang, and M.-C. Hong. "Numerical study for the impact of liquid droplets on solid surfaces." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 221, no. 3 (March 1, 2007): 293–301. http://dx.doi.org/10.1243/0954406jmes488.
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The impinging behaviour of liquid droplets on solid surfaces is studied using a computational approach. The analysis comprises the unsteady three-dimensional conservation equations of mass and momentum, with the surface tension effect treated by the continuous surface force model. Gas-liquid interfacial motions are simulated by the volume-of-fluid method in conjunction with the piecewise linear interface construction technique. In the computer code validation for a water droplet impacting on a polished stainless steel surface, computer-generated images of the time evolution of the droplet impingement dispersal shape are compared with magnified photographs by Pasandideh-Fard et al. The flow and transport phenomena in the impingement flowfield are further examined in detail. In order to respond to the need for its use in practical applications, the study is extended to explore the spreading progression to achieve a better understanding of the interaction of a 30 μm diameter polyethylenedioxy thiophene liquid droplet with a 50 × 50 μm indium tin oxide-coating square cavity at an impact velocity of 6 m/s.
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Sawaguchi, Erina, Ayumi Matsuda, Kai Hama, Masafumi Saito, and Yoshiyuki Tagawa. "Droplet levitation over a moving wall with a steady air film." Journal of Fluid Mechanics 862 (January 8, 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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Naoe, Takashi, and Masatoshi Futakawa. "Dynamic Behavior of Liquid Mercury Droplets Colliding with a Solid Surface." Applied Mechanics and Materials 566 (June 2014): 391–96. http://dx.doi.org/10.4028/www.scientific.net/amm.566.391.
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The dynamic behavior of liquid mercury and water droplets colliding with a solid surface were precisely examined as part of a fundamental study for investigating the behavior of a liquid microjet emitted as a result of a cavitation bubble collapse in mercury. Liquid droplets were collided with a quartz plate by the free-fall method, and the colliding and spreading behaviors of the liquids were observed using a high-speed video camera. In the case of mercury droplets, the spreading, recoiling, and jump-up phenomena resulting from the high surface tension of mercury were observed. The ratio of the maximum spreading diameter,Dmax, to the initial droplet diameter,D0, was investigated by parametrically changing the colliding velocity and tilt-angle of the quartz plate. The result showed that the ratioDmax/D0was well correlated with the Weber number, which is defined as a function of the colliding velocity and surface tension, independent of the liquid considered.
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Tığlı, Ahmet, and Tahir Çağın. "A Case Study on Metal-Ceramic Interfaces: Wetting of Alumina by Molten Aluminum." Materials Science Forum 915 (March 2018): 185–89. http://dx.doi.org/10.4028/www.scientific.net/msf.915.185.
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Interfacial behavior of Al and α-Al2O3 are investigated via molecular dynamic simulation (MD) employing reactive force fields parameterized for Al and Al2O3. The main result of this work is elucidating the wetting behavior and interface chemistry of molten aluminum on the α-Alumina (0001) surface through MD simulations. Wetting and interface chemistry are studied at 8 different temperatures from 700 to 1400 K for four different droplet sizes: with 16, 24, 32 and 40 Å diameters. Chemical reactions are observed at all temperatures and sizes in addition to diffusion between droplet and substrate atoms into each other during the wetting process. To define the level of wetting, we characterized contact angles of aluminum droplets on alumina substrates for all temperatures and sizes by using a method developed by Hautman and Klein. Chemical reactions are more extensive for the small droplets (16 and 24 Å) due to their larger surface to volume ratio in comparison to the larger droplets (32, and 40 Å) of droplets.
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Zhu, Xingye, Joseph Lewballah, Alexander Fordjour, Xiaoping Jiang, Junping Liu, Samuel Ofosu, and Frank Dwomoh. "Modelling of Water Drop Movement and Distribution in No Wind and Windy Conditions for Different Nozzle Sizes." Water 13, no. 21 (October 26, 2021): 3006. http://dx.doi.org/10.3390/w13213006.
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A numerical model was developed to determine the water drop movement and mean droplet size diameter at any distance from a sprinkler as a function of nozzle size and pressure. Droplet size data from 4, 5, 6, and 7 mm nozzle sizes verified the model. Data for model prediction were generated throughout lab experiments. The results demonstrated that the correlation between the observed and predicted droplet size diameter values for all the nozzle sizes and pressures is quite good. Nozzle size and pressure had a major influence on droplet size. Higher pressure produced smaller droplets over the entire application profile. The wetted distance downwind from the sprinkler increased as wind velocity increased, for example at a constant working pressure of 300 kPa, at wind speeds of 3.5 m/s and 4.5 m/s, 20% and 32% of the total volume exceeded the wet radius respectively. Larger droplets (3.9–4.5 mm), accounting for 3.6% and 6.3% of the total number of distributed droplets, respectively. The model can also predict the droplet size distribution at any wind direction overall the irrigated pattern.
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Armand, M., P. Borel, B. Pasquier, C. Dubois, M. Senft, M. Andre, J. Peyrot, J. Salducci, and D. Lairon. "Physicochemical characteristics of emulsions during fat digestion in human stomach and duodenum." American Journal of Physiology-Gastrointestinal and Liver Physiology 271, no. 1 (July 1, 1996): G172—G183. http://dx.doi.org/10.1152/ajpgi.1996.271.1.g172.
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Seven fasting subjects were fitted with nasogastric and nasoduodenal tubes and received intragastrically a coarsely emulsified test meal. Gastric and duodenal aspirates were collected after 1, 2, 3, and 4 h. In the duodenum, most lipids (> 90%) were present as emulsified droplets 1-100 microns in size. Large droplets and unemulsified material present in the test meal (> 100 micron) disappeared, whereas smaller droplets (1-50 microns) were generated after 1 h of digestion. Thus the median lipid droplet diameter significantly decreased (19.6 vs. 56.5 microns in the test meal) and the droplet surface area significantly increased (1.58 vs. 0.70 micron2/g fat). Intermediate droplet diameters were 34.3, 46.3, and 27.6 microns after 2, 3, and 4 h, respectively. In the stomach, a comparable emulsion particle size pattern was observed, with median droplet diameters of 17.2, 37.9, 52.4, and 41.6 microns after 1, 2, 3, and 4 h, respectively. However, the extent of triglyceride hydrolysis was much lower in the stomach (6-16%) than in the duodenum (42-45%), where small droplets were enriched in lipolytic products, cholesterol, and phospholipids. The present findings show for the first time that most dietary lipids are present in the human duodenum as emulsified droplets 1-50 microns in size and that no further marked emulsification of dietary fat occurs in the duodenum compared with the stomach.
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Konrad, Wilfried, and Anita Roth-Nebelsick. "Sorting of droplets by migration on structured surfaces." Beilstein Journal of Nanotechnology 2 (April 20, 2011): 215–21. http://dx.doi.org/10.3762/bjnano.2.25.
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Background: Controlled transport of microdroplets is a topic of interest for various applications. It is well known that liquid droplets move towards areas of minimum contact angle if placed on a flat solid surface exhibiting a gradient of contact angle. This effect can be utilised for droplet manipulation. In this contribution we describe how controlled droplet movement can be achieved by a surface pattern consisting of cones and funnels whose length scales are comparable to the droplet diameter. Results: The surface energy of a droplet attached to a cone in a symmetry-preserving way can be smaller than the surface energy of a freely floating droplet. If the value of the contact angle is fixed and lies within a certain interval, then droplets sitting initially on a cone can gain energy by moving to adjacent cones. Conclusion: Surfaces covered with cone-shaped protrusions or cavities may be devised for constructing “band-conveyors” for droplets. In our approach, it is essentially the surface structure which is varied, not the contact angle. It may be speculated that suitably patterned surfaces are also utilised in biological surfaces where a large variety of ornamentations and surface structuring are often observed.
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Guo, Chunfang, Lei Liu, and Changwan Liu. "Contact time of impacting droplets on a superhydrophobic surface with tunable curvature and groove orientation." Journal of Physics: Condensed Matter 34, no. 9 (December 10, 2021): 095001. http://dx.doi.org/10.1088/1361-648x/ac3c67.
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Abstract Regulating the impact dynamics of water droplets on a solid surface is of great significance for some practical applications. In this study, the droplet impingement on a flexible superhydrophobic surface arrayed with micro-scale grooves was investigated experimentally. The surface was curved into cylindrical shapes with certain curvatures from two orthogonal directions, where axial and circumferential grooves were formed, respectively. The effects of curvature diameter and Weber number, as well as the orientation of grooves on droplet spreading and retracting dynamics were analyzed and explained. Results show that the circumferential grooves promote the spreading of a droplet in the azimuthal direction, where the droplet rebounds from the surface with a stretched shape. This mechanism further reduces the contact time of impacting droplets on the superhydrophobic surface compared to the other curving mode.
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Nasser, Gamal A., Ahmed M. R. Fath El-Bab, Ahmed L. Abdel-Mawgood, Hisham Mohamed, and Abdelatty M. Saleh. "CO2 Laser Fabrication of PMMA Microfluidic Double T-Junction Device with Modified Inlet-Angle for Cost-Effective PCR Application." Micromachines 10, no. 10 (October 9, 2019): 678. http://dx.doi.org/10.3390/mi10100678.
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The formation of uniform droplets and the control of their size, shape and monodispersity are of utmost importance in droplet-based microfluidic systems. The size of the droplets is precisely tuned by the channel geometry, the surface interfacial tension, the shear force and fluid velocity. In addition, the fabrication technique and selection of materials are essential to reduce the fabrication cost and time. In this paper, for reducing the fabrication cost Polymethyl methacrylate (PMMA) sheet is used with direct write laser technique by VERSA CO2 laser VLS3.5. This laser writing technique gives minimum channel width of about 160 μ m , which limit miniaturizing the droplet. To overcome this, modification on double T-junction (DTJ) channel geometry has been done by modifying the channel inlets angles. First, a two-dimensional (2D) simulation has been done to study the effect of the new channel geometry modification on droplet size, droplets distribution inside the channel, and its throughput. The fabricated modified DTJ gives the minimum droplet diameter of 39 ± 2 μ m , while DTJ channel produced droplet diameter of 48 ± 4 μ m at the same conditions. Moreover, the modified double T-junction (MDTJ) decreases the variation in droplets diameter at the same flow rates by 4.5 – 13 % than DTJ. This low variation in the droplet diameter is suitable for repeatability of the DNA detection results. The MDTJ also enhanced the droplet generation frequency by 8 – 25 % more than the DTJ channel. The uniformity of droplet distribution inside the channel was enhanced by 3 – 20 % compared to the DTJ channel geometry. This fabrication technique eliminates the need for a photomask and cleanroom environment in addition shortening the cost and time. It takes only 20 min for fabrication. The minimum generated droplet diameter is within 40 μ m with more than 1000 droplets per second (at 10 mL / h . oil flow rate). The device is a high-throughput and low-cost micro-droplet formation aimed to be as a front-end to a dynamic droplet digital PCR (ddPCR) platform for use in resource-limited environment.
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Ku Shaari, Ku Zilati, and Richard Turton. "The Study of Droplet Impact Behavior on Flat Surface with Different Surface Properties." Defect and Diffusion Forum 297-301 (April 2010): 19–24. http://dx.doi.org/10.4028/www.scientific.net/ddf.297-301.19.
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The impact behavior of a liquid droplet on solid surface is a complex phenomenon and yet is a basic component of various industrial processes particularly in the pharmaceutical industry. In this industry, film coating technique is used in tablet coating, in which coating uniformity is important especially if the coating is for functional purposes. Coating uniformity on a tablet could be affected by several factors, one of which is the impingements of droplets on its surface. In this work, the maximum spreading diameter and the initial impact behavior of a single droplet on pharmaceutical tablet surfaces and metal surfaces having different surface properties are investigated. A Charged-Coupled-Device (CCD) high-speed camera with framing rate of 2,000, attached to a 10X microscope, was used to capture the phenomena. The results show that the initial impact behavior of a droplet is not affected by the porosity of a surface. The results on the pharmaceutical tablets, stainless steel and etched silicon surfaces show that the rougher the surface the lower the spreading factor. The droplets on all surfaces demonstrate that a droplet that produces higher spreading factor gives a lower bouncing factor.
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Chen, Chun-Kuei, Sheng-Qi Chen, Wei-Mon Yan, Wen-Ken Li, and Ta-Hui Lin. "Experimental study on two consecutive droplets impacting onto an inclined solid surface." Journal of Mechanics 37 (2021): 432–45. http://dx.doi.org/10.1093/jom/ufab012.
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Abstract The present study is concerned with the experimental impingement of two consecutive droplets on an inclined solid surface. Attention is mainly paid to the effects of impingement timing with various oblique angles (Φ) of the surface on the impact phenomena, which mainly affect the maximum droplet spreading diameter. The investigation considers four impingement scenarios differentiated by impingement timing, namely Case 1: single-droplet impingement; Case 2 of Δt1: the moment when the leading droplet starts spreading along the oblique surface; Case 3 of Δt2: the moment when the leading droplet reaches its maximum spreading; and Case 4 of Δt3: the moment when the leading droplet starts retracting. It is observed that deformation behavior of two successive droplets impacting on the inclined surface experiences a complex asymmetric morphology evolution due to the enhancement of gravity effect and various conditions of the impingement timing. The merged droplet becomes slender with increasing oblique surface angle in the final steady shape, causing the decrease in the value of front and back contact angles. The impingement timing has a significant influence on the change of the maximum height of the merged droplet. The coalesced droplet spreads to the maximum dimensionless width diameter at Δt = Δt2 and the oblique angle of Φ = 45°, but reaches the maximum dimensionless height for Δt = Δt2 at Φ = 30°. The front contact angles converge to a fixed value eventually for all conditions of impingement timing, and the values become lower with the increasing surface inclination.
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He, Zhong, Zengzilu Xia, Mengying Zhang, Jinbo Wu, and Weijia Wen. "Calcium Carbonate Mineralization in a Surface-Tension-Confined Droplets Array." Crystals 9, no. 6 (May 30, 2019): 284. http://dx.doi.org/10.3390/cryst9060284.
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Calcium carbonate biomimetic crystallization remains a topic of interest with respect to biomineralization areas in recent research. It is not easy to conduct high-throughput experiments with only a few macromolecule reagents using conventional experimental methods. However, the emergence of microdroplet array technology provides the possibility to solve these issues efficiently. In this article, surface-tension-confined droplet arrays were used to fabricate calcium carbonate. It was found that calcium carbonate crystallization can be conducted in surface-tension-confined droplets. Defects were found on the surface of some crystals, which were caused by liquid flow inside the droplet and the rapid drop in droplet height during the evaporation. The diameter and number of crystals were related to the droplet diameter. Polyacrylic acid (PAA), added as a modified organic molecule control, changed the CaCO3 morphology from calcite to vaterite. The material products of the above experiments were compared with bulk-synthesized calcium carbonate by scanning electron microscopy (SEM), Raman spectroscopy and other characterization methods. Our work proves the possibility of performing biomimetic crystallization and biomineralization experiments on surface-tension-confined microdroplet arrays.
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Jankowski, Antoni, and Mirosław Kowalski. "Influence of the quality of fuel atomization on the emission of exhaust gases toxic components of combustion engines." Journal of KONBiN 36, no. 1 (December 1, 2015): 43–50. http://dx.doi.org/10.1515/jok-2015-0055.
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Abstract The paper contains analysis of the impact on the quality of the fuel spray of droplets on the number and the value of the surface area of the droplets that have a direct impact on the efficiency of the combustion process. It presents a change in the level of toxic exhaust emissions with an increase in the so-called. Sauter Mean Diameter (SMD) of fuel droplets. The presented figures show that the increase in the average droplet diameter SMD in particular causes an increase of toxic exhaust gases emissions, i.e. mainly nitrogen oxides NO, carbon monoxide CO, hydrocarbons HC and Particulate Matter (PM). This tendency is not constant, because it is changing according to changes of the coefficient of equivalence Φ. For example, emissions of nitrogen oxides for the lean mixtures (Φ <1), with an increase in average droplet diameter increases, while now for the rich mixtures (Φ> 1), this trend is significantly changed, i.e. the level of this emission decreases.
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Qilei, Guo. "Numerical study of low-speed droplets impacting on the fabric surface." Mechanics 25, no. 6 (December 4, 2019): 449–54. http://dx.doi.org/10.5755/j01.mech.25.6.22947.
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In this approach, the numerical model of the fluid dynamics of liquid droplets impacting on the fabric surface with VOF method is proposed. The results obtained by the proposed model are well in agreement with the experimental results. The mechanism of the liquid droplet morphological evolution is investigated by pressure distribution and velocity vector, and the obvious bubble entrapment, which cannot be observed in experimenal results, is captured by the proposed model. The evolution laws of the spreading factor and the contact angle at the liquid-porous interface are obtained and the reason why the contact angle is dynamic is analyzed. The effects of droplet diameter and impact velocity on the fluid flow characteristics are also discussed. Usually, droplet diameter increasing leads more dramatic shape distortion of the liquid droplet, and impact velocity increasing leads shorter time to reach the maximum spreading stage. Finally, based on the properties of the impacting droplet by the proposed model, the important references of optimizing the parachute design for severe weather are built.
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Schroder, J. C., S. J. Hanna, R. L. Modini, A. L. Corrigan, S. M. Kreidenwies, A. M. Macdonald, K. J. Noone, L. M. Russell, W. R. Leaitch, and A. K. Bertram. "Size-resolved observations of refractory black carbon particles in cloud droplets at a marine boundary layer site." Atmospheric Chemistry and Physics 15, no. 3 (February 9, 2015): 1367–83. http://dx.doi.org/10.5194/acp-15-1367-2015.
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Abstract. Size-resolved observations of aerosol particles and cloud droplet residuals were studied at a marine boundary layer site (251 m a.m.s.l.) in La Jolla, San Diego, California, during 2012. A counterflow virtual impactor (CVI) was used as the inlet to sample cloud residuals while a total inlet was used to sample both cloud residuals and interstitial particles. Two cloud events totaling 10 h of in-cloud sampling were analyzed. Based on bulk aerosol particle concentrations, mass concentrations of refractory black carbon (rBC), and back trajectories, the two air masses sampled were classified as polluted marine air. Since the fraction of cloud droplets sampled by the CVI was less than 100%, the measured activated fractions of rBC should be considered as lower limits to the total fraction of rBC activated during the two cloud events. Size distributions of rBC and a coating analysis showed that sub-100 nm rBC cores with relatively thick coatings were incorporated into the cloud droplets (i.e., 95 nm rBC cores with median coating thicknesses of at least 65 nm were incorporated into the cloud droplets). Measurements also show that the coating volume fraction of rBC cores is relatively large for sub-100 nm rBC cores. For example, the median coating volume fraction of 95 nm rBC cores incorporated into cloud droplets was at least 0.9, a result that is consistent with κ-Köhler theory. Measurements of the total diameter of the rBC-containing particles (rBC core and coating) suggest that the total diameter of rBC-containing particles needed to be at least 165 nm to be incorporated into cloud droplets when the core rBC diameter is ≥ 85 nm. This result is consistent with previous work that has shown that particle diameter is important for activation of non-rBC particles. The activated fractions of rBC determined from the measurements ranged from 0.01 to 0.1 for core rBC diameters ranging from 70 to 220 nm. This type of data is useful for constraining models used for predicting rBC concentrations in the atmosphere.
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Dodd, Michael S., and Antonino Ferrante. "On the interaction of Taylor length scale size droplets and isotropic turbulence." Journal of Fluid Mechanics 806 (September 30, 2016): 356–412. http://dx.doi.org/10.1017/jfm.2016.550.
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Droplets in turbulent flows behave differently from solid particles, e.g. droplets deform, break up, coalesce and have internal fluid circulation. Our objective is to gain a fundamental understanding of the physical mechanisms of droplet–turbulence interaction. We performed direct numerical simulations (DNS) of 3130 finite-size, non-evaporating droplets of diameter approximately equal to the Taylor length scale and with 5 % droplet volume fraction in decaying isotropic turbulence at initial Taylor-scale Reynolds number $\mathit{Re}_{\unicode[STIX]{x1D706}}=83$. In the droplet-laden cases, we varied one of the following three parameters: the droplet Weber number based on the r.m.s. velocity of turbulence ($0.1\leqslant \mathit{We}_{rms}\leqslant 5$), the droplet- to carrier-fluid density ratio ($1\leqslant \unicode[STIX]{x1D70C}_{d}/\unicode[STIX]{x1D70C}_{c}\leqslant 100$) or the droplet- to carrier-fluid viscosity ratio ($1\leqslant \unicode[STIX]{x1D707}_{d}/\unicode[STIX]{x1D707}_{c}\leqslant 100$). In this work, we derive the turbulence kinetic energy (TKE) equations for the two-fluid, carrier-fluid and droplet-fluid flow. These equations allow us to explain the pathways for TKE exchange between the carrier turbulent flow and the flow inside the droplet. We also explain the role of the interfacial surface energy in the two-fluid TKE equation through the power of the surface tension. Furthermore, we derive the relationship between the power of surface tension and the rate of change of total droplet surface area. This link allows us to explain how droplet deformation, breakup and coalescence play roles in the temporal evolution of TKE. Our DNS results show that increasing $\mathit{We}_{rms}$, $\unicode[STIX]{x1D70C}_{d}/\unicode[STIX]{x1D70C}_{c}$ and $\unicode[STIX]{x1D707}_{d}/\unicode[STIX]{x1D707}_{c}$ increases the decay rate of the two-fluid TKE. The droplets enhance the dissipation rate of TKE by enhancing the local velocity gradients near the droplet interface. The power of the surface tension is a source or sink of the two-fluid TKE depending on the sign of the rate of change of the total droplet surface area. Thus, we show that, through the power of the surface tension, droplet coalescence is a source of TKE and breakup is a sink of TKE. For short times, the power of the surface tension is less than $\pm 5\,\%$ of the dissipation rate. For later times, the power of the surface tension is always a source of TKE, and its magnitude can be up to 50 % of the dissipation rate.
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Ozel Erol, Gulcan, and Nilanjan Chakraborty. "Effects of Mean Inflow Velocity and Droplet Diameter on the Propagation of Turbulent V-Shaped Flames in Droplet-Laden Mixtures." Fluids 6, no. 1 (December 22, 2020): 1. http://dx.doi.org/10.3390/fluids6010001.
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Three-dimensional carrier phase Direct Numerical Simulations of V-shaped n-heptane spray flames have been performed for different initially mono-sized droplet diameters to investigate the influence of mean flow velocity on the burning rate and flame structure at different axial locations from the flame holder. The fuel is supplied as liquid droplets through the inlet and an overall (i.e., liquid + gaseous) equivalence ratio of unity is retained in the unburned gas. Additionally, turbulent premixed stoichiometric V-shaped n-heptane flames under the same turbulent flow conditions have been simulated to distinguish the differences in combustion behaviour of the pure gaseous phase premixed combustion in comparison to the corresponding behaviour in the presence of liquid n-heptane droplets. It has been found that reacting gaseous mixture burns predominantly under fuel-lean mode and the availability of having fuel-lean mixture increases with increasing mean flow velocity. The extent of flame wrinkling for droplet cases has been found to be greater than the corresponding gaseous premixed flames due to flame-droplet-interaction, which is manifested by dimples on the flame surface, and this trend strengthens with increasing droplet diameter. As the residence time of the droplets within the flame decreases with increasing mean inflow velocity, the droplets can survive for larger axial distances before the completion of their evaporation for the cases with higher mean inflow velocity and this leads to greater extents of flame-droplet interaction and droplet-induced flame wrinkling. Mean inflow velocity, droplet diameter and the axial distance affect the flame brush thickness. The flame brush thickens with increasing droplet diameter for the cases with higher mean inflow velocity due to the predominance of fuel-lean gaseous mixture within the flame. However, an opposite behaviour has been observed for the cases with lower mean inflow velocity where the smaller extent of flame wrinkling due to smaller values of integral length scale to flame thickness ratio arising from higher likelihood of fuel-lean combustion for larger droplets dominates over the thickening of the flame front. It has been found that the major part of the heat release arises due to premixed mode of combustion for all cases but the contribution of non-premixed mode of combustion to the total heat release has been found to increase with increasing mean inflow velocity and droplet diameter. The increase in the mean inflow velocity yields an increase in the mean values of consumption and density-weighted displacement speed for the droplet cases but leads to a decrease in turbulent burning velocity. By contrast, an increase in droplet diameter gives rise to decreases in turbulent burning velocity, and the mean values of consumption and density-weighted displacement speeds. Detailed physical explanations have been provided to explain the observed mean inflow velocity and droplet diameter dependences of the flame propagation behaviour.
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Liu, Xin, Xuan Zhang, and Jingchun Min. "Droplet rebound and dripping during impact on small superhydrophobic spheres." Physics of Fluids 34, no. 3 (March 2022): 032118. http://dx.doi.org/10.1063/5.0083833.
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While droplet impact processes on hydrophilic and hydrophobic spheres have been widely investigated experimentally and numerically, the impact behaviors of water droplets on small superhydrophobic spheres are studied numerically and theoretically in this research. The numerical model adopts the volume of fluid method (VOF) and is verified by comparing the simulation results with the experimental observations in the literature. The effects of Weber number and sphere-to-droplet diameter ratio on the droplet impact dynamics are discussed. The final outcomes of the impact droplets are classified into rebound and dripping types with the latter appearing at a larger Weber number or a smaller diameter ratio. As the Weber number and diameter ratio increase, droplet deformation during impact is reinforced with the maximum width factor of the rebound droplet becoming greater. The maximum width factor of the dripping droplet is nearly independent of the Weber number but is enlarged by the increasing diameter ratio. Moreover, a larger diameter ratio reduces the contact time of the rebound droplet but raises that of the dripping one. A theoretical model based on energy conservation is established to predict the boundary between the droplet rebound and dripping outcomes and is in good agreement with the simulation results. The diameter ratio limit for droplet dripping at a zero Weber number is also obtained. Our results and analyses provide insight into the interaction mechanism between the impact droplet and small spheres or particles.
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Ochowiak, Marek, Sylwia Włodarczak, Ivan Pavlenko, Daniel Janecki, Andżelika Krupińska, and Małgorzata Markowska. "Study on Interfacial Surface in Modified Spray Tower." Processes 7, no. 8 (August 13, 2019): 532. http://dx.doi.org/10.3390/pr7080532.
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This paper presents an analysis of the changes in interfacial surface and the size of droplets formed in a spray tower. The interfacial surface and the size of droplets formed are of fundamental importance to the performance of the equipment, both in terms of pressure drop and process efficiency. Liquid film and droplet sizes were measured using a microphotography technique. The confusors studied were classical, with profiled inside surface, and with double profiled inside surface. The liquids studied were water and aqueous solutions of high-molecular polyacrylamide (PAA) of power-law characteristics. The ranges of process Reynolds number studied were as follows: ReG ∈ (42,700; 113,000), ReL ∈ (170; 15,200). A dimensionless correlation for reduced Sauter mean diameter is proposed.
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Tian, Lu, Zi Ye, and Lin Gui. "A Study of Dielectrophoresis-Based Liquid Metal Droplet Control Microfluidic Device." Micromachines 12, no. 3 (March 23, 2021): 340. http://dx.doi.org/10.3390/mi12030340.
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This study presents a dielectrophoresis-based liquid metal (LM) droplet control microfluidic device. Six square liquid metal electrodes are fabricated beneath an LM droplet manipulation pool. By applying different voltages on the different electrodes, a non-uniform electric field is formed around the LM droplet, and charges are induced on the surface of the droplet accordingly, so that the droplet could be driven inside the electric field. With a voltage of ±1000 V applied on the electrodes, the LM droplets are driven with a velocity of 0.5 mm/s for the 2.0 mm diameter ones and 1.0 mm/s for the 1.0 mm diameter ones. The whole chip is made of PDMS, and microchannels are fabricated by laser ablation. In this device, the electrodes are not in direct contact with the working droplets; a thin PDMS film stays between the electrodes and the driven droplets, preventing Joule heat or bubble formation during the experiments. To enhance the flexibility of the chip design, a gallium-based alloy with melting point of 10.6 °C is used as electrode material in this device. This dielectrophoresis (DEP) device was able to successfully drive liquid metal droplets and is expected to be a flexible approach for liquid metal droplet control.
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Wang, Fei, Lin Wang, and Guoding Chen. "Analysis of Oil Droplet Deposition Characteristics and Determination of Impact State Criterion in Aero-Engine Bearing Chamber." Processes 8, no. 6 (June 25, 2020): 741. http://dx.doi.org/10.3390/pr8060741.
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The research of oil/air two-phase flow and heat transfer is the fundamental work of the design of lubrication and heat transfer in aero-engine bearing chamber. The determination of impact state criterion of the moving oil droplets with the wall and the analysis of oil droplet deposition characteristics are important components. In this paper, the numerical analysis model of the impact between the moving oil droplet and the wall is established by using the finite volume method, and the simulation of oil droplet impingement on the wall is carried out. Then the effects of oil droplet diameter, impact velocity, and incident angle on the characteristic parameters of impact state are discussed. The characteristic parameters include the maximum spreading length, the maximum spreading width, and the number of splashing oil droplets. Lastly the calculation results are verified through comparing with the experimental results in the literature. The results show as follows: (1) The maximum spreading width of oil droplet firstly increases and then slows down with the incident angle and the oil droplet diameter increasing; (2) when the oil droplet diameter becomes small, the influence of the incident angle on the maximum spreading length of oil droplet is obvious and vice versa; (3) with the impact velocity and diameter of oil droplet increasing, the maximum spreading width of oil droplet increases firstly and then slows down, and the maximum spreading length increased gradually; (4) the number of splashing oil droplets increases with the incident angle and impact velocity increasing; and (5) compared with the experimental data in literature, the critical dimensionless splashing coefficient K c proposed in this paper can better distinguish the impact state of oil droplet.
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Shrestha, Rekha Goswami, Tatsuya Ando, Yukihiro Sakamoto, and Jin Kawakita. "Enhancement of Sensitivity and Accuracy of Micro/Nano Water Droplets Detection Using Galvanic-Coupled Arrays." Sensors 19, no. 20 (October 17, 2019): 4500. http://dx.doi.org/10.3390/s19204500.
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A moisture sensor has been reported that detects invisibly small water droplets and distinguishes their particle size with high accuracy and high speed. This sensor uses narrow lines of dissimilar metals as electrodes, arranged with gaps of 0.5 to 10 μm. The working principle for this sensor is that it measures the galvanic current generated when a water droplet forms a bridge-like structure between the electrodes. In addition, the surface of the sensor was controlled by using hydrophilic polymer, GL, and hydrophobic polymer, PMMA. The study of the relationship between the contact angle, projected area of water droplets and current response from the sensor with a modified surface showed that in the case of GL, the contact angle was small (wettability increased) and the average value and distribution of the projected water droplet area and the sensor’s response increased. This enhanced the sensor’s sensitivity. On the other hand, in the case of PMMA, the contact angle was large (wettability decreased), the area of the water droplet and its distribution became small and the accuracy of discriminating the water droplet’s diameter by the sensor enhanced. Therefore, by rendering sensor’s surface hydrophilic and hydrophobic, the sensitivity and accuracy of the sensor could be enhanced.
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Wang, Fei, Lin Wang, Guoding Chen, and Donglei Zhu. "Numerical Simulation of the Oil Droplet Size Distribution Considering Coalescence and Breakup in Aero-Engine Bearing Chamber." Applied Sciences 10, no. 16 (August 14, 2020): 5648. http://dx.doi.org/10.3390/app10165648.
Full textAbstract:
In order to improve the inadequacy of the current research on oil droplet size distribution in aero-engine bearing chamber, the influence of oil droplet size distribution with the oil droplets coalescence and breakup is analyzed by using the computational fluid dynamics-population balance model (CFD-PBM). The Euler–Euler equation and population balance equation are solved in Fluent software. The distribution of the gas phase velocity field and the volume fraction of different oil droplet diameter at different time are obtained in the bearing chamber. Then, the influence of different initial oil droplet diameter, air, and oil mass flow on oil droplet size distribution is discussed. The result of numerical analysis is compared with the experiment in the literature to verify the feasibility and validity. The main results provide the following conclusions. At the initial stage, the coalescence of oil droplets plays a dominant role. Then, the breakup of larger diameter oil droplet appears. Finally, the oil droplet size distribution tends to be stable. The coalescence and breakup of oil droplet increases with the initial diameter of oil droplet and the air mass flow increasing, and the oil droplet size distribution changes significantly. With the oil mass flow increasing, the coalescence and breakup of oil droplet has little change and the variation of oil droplet size distribution is not obvious.