Journal articles on the topic 'Droplet velocity distribution'
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1
Wang, Junpeng, Cuicui Xu, Gang Zhou, and Yansong Zhang. "Spray Structure and Characteristics of a Pressure-Swirl Dust Suppression Nozzle Using a Phase Doppler Particle Analyze." Processes 8, no. 9 (September 10, 2020): 1127. http://dx.doi.org/10.3390/pr8091127.
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In order to understand the characteristics of the spray field of a dust suppression nozzle and provide a reference for dust nozzle selection according to dust characteristics, a three-dimensional phase Doppler particle analyzer (PDPA) spray measurement system is used to analyze the droplet size and velocity characteristics in a spray field, particularly the joint particle size–velocity distribution. According to the results, after the ejection of the jet from the nozzle, the droplets initially maintained some velocity; however, the distribution of particles with different sizes was not uniform. As the spray distance increased, the droplet velocity decreased significantly, and the particle size distribution changed very little. As the distance increased further, the large droplets separated into smaller droplets, and their velocity decreased rapidly. The distributions of the particle size and velocity of the droplets then became stable. Based on the particle size-velocity distribution characteristics, the spray structure of pressure-swirl nozzles can be divided into five regions, i.e., the mixing, expansion, stabilization, decay, and rarefied regions. The expansion, stabilization, and decay regions are the effective dust fall areas. In addition, the droplet size in the stabilization region is the most uniform, indicating that this region is the best dust fall region. The conclusions can provide abundant calibration data for spray dust fall nozzles.
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Sun, Yicheng, Yufan Fu, Baohui Chen, Jiaxing Lu, and Wanquan Deng. "Numerical Simulation and Experimental Study on Flow Field in a Swirl Nozzle." Shock and Vibration 2021 (January 25, 2021): 1–9. http://dx.doi.org/10.1155/2021/6626715.
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In order to study the internal flow characteristics and external droplet velocity distribution characteristics of the swirl nozzle, the following methods were used: numerical simulations were used to study the internal flow characteristics of a swirl nozzle and phase Doppler particle velocimetry was used to determine the corresponding external droplet velocity distribution under medium and low pressure conditions. The distributions of pressure and water velocity inside the nozzle were obtained. Meanwhile, the velocities of droplets outside the nozzle in different sections were discussed. The results show that the flow rate in the swirl nozzle increases with the increase in inlet pressure, and the local pressure in the region decreases because of the excessive velocity at the internal outlet section of the swirl nozzle, resulting in cavitation. The experimental results show that under an external flow field, the minimum droplet velocity occurs in the axial direction; starting from the axis, the velocity first increases and then decreases along the radial direction. Swirling motion inside the nozzle and velocity variations in the external flow field occur under medium and low pressure conditions. The relationship between the inlet pressure and the distributions of water droplets’ velocities was established, which provides a reference for the research and development of the swirl nozzle.
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Li, Xinpeng, Liping Chen, Qin Tang, Longlong Li, Wu Cheng, Peng Hu, and Ruirui Zhang. "Characteristics on the Spatial Distribution of Droplet Size and Velocity with Difference Adjuvant in Nozzle Spraying." Agronomy 12, no. 8 (August 19, 2022): 1960. http://dx.doi.org/10.3390/agronomy12081960.
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The spatial distribution of droplet size and velocity affects the deposition and distribution on the target. In order to investigate the influence of different adjuvant and pressures on the spatial distribution of droplet size and velocity in atomization area of different nozzles, air induction flat fan nozzle IDK120-03, multi-range flat fan nozzle LU120-03 and anti-drift flat fan nozzle AD120-03 were selected. Phase Doppler Interferometer (PDI) was used to analyze and compare the distribution of droplet size and velocity in the atomization area of three nozzles when four typical adjuvant Maisi, Maidao, Adsee AB-600 and Surun sprayed at different pressures. The results show that the volume median diameter of droplet size has no obvious change along the vertical direction of the nozzle center and increases with distance in the horizontal direction, the droplet size decreases with increasing pressure at the same position, the adjuvant all increases the droplet size (about 12%, 12%, 10% and 9% for Maisi, Maidao, Surun and Adsee AB-600, respectively), IDK120-03 nozzle droplet size is the largest and LU120-03 nozzle is the smallest in the same position. For droplet velocity distribution, droplet velocity decrease in distance along the vertical and horizontal direction, respectively, the droplet velocity increases with increasing pressure at the same position, compared with water, the droplet velocity increased by about 13%, 9%, 8%, and 4% for Maisi, Maidao, Surun, and Adsee AB-600, respectively, the velocity of AD nozzle is the largest and IDK nozzle is the smallest at the same position. The experiment can provide a basis for the selection of adjuvants and nozzles in pesticide application, and provide a data base for studying the distribution of droplets on the target.
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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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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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Yan, Ming De, Han Ping Mao, and Wei Dong Jia. "Experimental Study on the Gas-Liquid Two Phase Flow of Air-Assist Boom Spraying." Applied Mechanics and Materials 341-342 (July 2013): 371–74. http://dx.doi.org/10.4028/www.scientific.net/amm.341-342.371.
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The velocity and diameter distribution of the air-assist boom spraying is studied by a laser Phase Doppler Partic1e Analyzer when the operational parameters is changed, which including airflow velocity of air curtain and vertical relative position between the air curtain and the nozzle. From the experimental results, we find the as the air curtain velocity increases , the size distribution of the droplet is conducive to uniform . At the same air curtain velocity, droplet size decreases with increasing of nozzle pressure. On the right side of each measuring point, the number of droplets is gradual decreasing with the wind velocity increasing.When the working pressure is 0.5Mpa, the droplet size does not change with the change of the horizontal distance.
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Sardina, Gaetano, Stéphane Poulain, Luca Brandt, and Rodrigo Caballero. "Broadening of Cloud Droplet Size Spectra by Stochastic Condensation: Effects of Mean Updraft Velocity and CCN Activation." Journal of the Atmospheric Sciences 75, no. 2 (January 24, 2018): 451–67. http://dx.doi.org/10.1175/jas-d-17-0241.1.
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Abstract The authors study the condensational growth of cloud droplets in homogeneous isotropic turbulence by means of a large-eddy simulation (LES) approach. The authors investigate the role of a mean updraft velocity and of the chemical composition of the cloud condensation nuclei (CCN) on droplet growth. The results show that a mean constant updraft velocity superimposed onto a turbulent field reduces the broadening of the droplet size spectra induced by the turbulent fluctuations alone. Extending the authors’ previous results regarding stochastic condensation, the authors introduce a new theoretical estimation of the droplet size spectrum broadening that accounts for this updraft velocity effect. A similar reduction of the spectra broadening is observed when the droplets reach their critical size, which depends on the chemical composition of CCN. The analysis of the square of the droplet radius distribution, proportional to the droplet surface, shows that for large particles the distribution is purely Gaussian, while it becomes strongly non-Gaussian for smaller particles, with the left tail characterized by a peak around the haze activation radius. This kind of distribution can significantly affect the later stages of the droplet growth involving turbulent collisions, since the collision probability kernel depends on the droplet size, implying the need for new specific closure models to capture this effect.
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Meng, Yanhua, Wanqiang Zhong, Yue Liu, Meimei Wang, and Yubin Lan. "Droplet Distribution of an Autonomous UAV-based Sprayer in Citrus Tree Canopy." Journal of Physics: Conference Series 2203, no. 1 (February 1, 2022): 012022. http://dx.doi.org/10.1088/1742-6596/2203/1/012022.
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Abstract Although Unmanned Aerial Vehicles (UAVs) are developed for military missions originally, they have been used widely in civil activities for several decades globally. In agricultural, UAVs have been developed as an efficient sprayer for pesticide application since 1987. UAV-based sprayers are popular for the prevention and control of pests and diseases in field crop in many countries recently. Some of the UAV-based sprayers are developed to be equipped with fruit tree mode aiming at solving droplet penetration in the inside and bottom part of the fruit tree canopy. In this study, a newly released UAV-based sprayer (i.e., T30) equipped fruit tree mode is chosen as spraying platform to optimize the spraying parameters for practical application. The flight velocity and application rate are the variables, while droplet coverage, density, size, and penetration are the observed metrics. Three treatments with different flight velocities (2 m s-1 or 3 m s-1) or application rates (60 L ha-1 or 75 L ha-1) are arranged to collect the droplets for assessment. Water Sensitive Papers (WSPs) are placed in the outside, bottom, and inside layers of the canopy to collect droplets. The results show that the treatment combined a flight velocity of 2 m s-1 and an application rate of 60 L ha-1 obtains the most droplets among all the variables based on the values of droplet coverage and density. The treatment with a flight velocity of 2 m s-1 and an application rate of 75 L ha-1 has the best penetration, while the treatment with a velocity of 2 m s-1 and an application rate of 60 L ha-1 takes the second place according to the percentages of droplet deposition in the three layers. Overall consideration of the total droplet distribution and penetration of the application parameters, a flight velocity of 2 m s-1 and an application rate of 60 L ha-1 are recommended to get an ideal droplet distribution in tree canopy when UAV-based sprayer T30 equipped with fruit tree mode flies at 1.6∼2 m above the citrus tree canopy.
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Jia, Wei Dong, Cheng Li, Jun Lu, Ning Yang, and Zhen Tao Wang. "CFD Simulation of Spraying with Air Jet." Advanced Materials Research 455-456 (January 2012): 228–33. http://dx.doi.org/10.4028/www.scientific.net/amr.455-456.228.
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Droplet drift is always an accompaniment of pesticide spraying and can cause serious consequences. In this paper, we used a computational fluid dynamics software package (FLUENT) to analyze flow fields of spraying with air jet under different conditions in the tunnel model, and compared the effect of air jet on spray deposition and drift. Results of this study indicate that air jet can act directly on the spray droplets and affect their distribution and movement. Larger jet velocity has better performance on the drift reduction and droplet deposition. Droplets in the flow fields with larger jet velocity can get more kinetic energy and arrive at the root of crops easilier. When droplets are released straight down, larger velocity of droplets can be given and better performance can be achieved either in terms of drift reduction or droplet deposition.
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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.
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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.
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Jiang, Feng, Weilin Xu, Jun Deng, and Wangru Wei. "Flow Structures of the Air-Water Layer in the Free Surface Region of High-Speed Open Channel Flows." Mathematical Problems in Engineering 2020 (November 3, 2020): 1–10. http://dx.doi.org/10.1155/2020/5903763.
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In hydraulic engineering, intense free surface breakups have been observed to develop in high-speed open channel flows, resulting in a mixed air-water layer near the free surface that grows with the development of self-aeration. This region is characterized by a substantial number of droplets coexisting with an induced air layer above. Little information about this droplet layer is currently available and no practicable approach has been proposed for predicting the parameters of the induced air layer based on the related flow structures in the droplet layer. In this research, laboratory experiments were accordingly conducted to observe the detailed droplet layer development in terms of layer thickness, droplet size, and frequency distributions under comparative flow conditions. Based on the simplified droplet layer roughness determined using the experimentally measured mean droplet size, the classical power-law of boundary layer theory was applied to provide an analytical solution for the air velocity profile inside the air layer. The relationship of air layer growth to droplet layer thickness, which is a key factor when determining the air velocity distribution, was also established, and the analytical results were proven to be in reasonable agreement with air velocity profiles presented in the literature. By determining the relationship between droplet layer properties and air velocity profiles, the study establishes a basis for the improved modeling of high-speed open channel flows.
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KHOSID, S., and Y. TAMBOUR. "Analytic study of developing flows in a tube laden with non-evaporating and evaporating drops via a modified linearization of the two-phase momentum equations." Journal of Fluid Mechanics 603 (April 30, 2008): 245–70. http://dx.doi.org/10.1017/s0022112008001134.
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A novel modification of the classical Langhaar linearization of the mutually coupled momentum equations for developing two-phase flows in circular ducts is presented. This modification enables us to treat: (i) flows developing from spatially periodic initial velocity distributions without the presence of droplets, and (ii) two-phase flows in which monosize, non-evaporating and evaporating droplets suspended in a developing gas flow of an initially uniform velocity distribution exchange momentum with the host-gas flow. New solutions are presented for the downstream evolution in the velocity profiles which develop from spatially periodic initial velocity distributions that eventually reach the fully developed Poiseuille velocity profile. These solutions are validated by employing known numerical procedures, providing strong support for the physical underpinnings of the present modified linearization. New solutions are also presented for the evolution in drop velocities and vapour spatial distributions for evaporating droplets suspended in an initially uniform velocity profile of the host gas. Asymptotic solutions are presented for the flow region which lies very close to the inlet of the tube, where the relative velocity between the droplets and the host gas is high, and thus the velocity fields of the two phases are mutually coupled. These solutions provide new explicit formulae for the droplet velocity field as a function of the initial conditions and droplet diameter (relative to the tube diameter) for non-evaporating drops, and also as a function of evaporation rate for evaporating drops.
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Tolpadi, A. K., D. L. Burrus, and R. J. Lawson. "Numerical Computation and Validation of Two-Phase Flow Downstream of a Gas Turbine Combustor Dome Swirl Cup." Journal of Engineering for Gas Turbines and Power 117, no. 4 (October 1, 1995): 704–12. http://dx.doi.org/10.1115/1.2815456.
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The two-phase axisymmetric flow field downstream of the swirl cup of an advanced gas turbine combustor is studied numerically and validated against experimental Phase-Doppler Particle Analyzer (PDPA) data. The swirl cup analyzed is that of a single annular GE/SNECMA CFM56 turbofan engine that is comprised of a pair of coaxial counterswirling air streams together with a fuel atomizer. The atomized fuel mixes with the swirling air stream, resulting in the establishment of a complex two-phase flow field within the swirl chamber. The analysis procedure involves the solution of the gas phase equations in an Eulerian frame of reference using the code CONCERT. CONCERT has been developed and used extensively in the past and represents a fully elliptic body-fitted computational fluid dynamics code to predict flow fields in practical full-scale combustors. The flow in this study is assumed to be nonreacting and isothermal. The liquid phase is simulated by using a droplet spray model and by treating the motion of the fuel droplets in a Lagrangian frame of reference. Extensive PDPA data for the CFM56 engine swirl cup have been obtained at atmospheric pressure by using water as the fuel (Wang et al., 1992a). The PDPA system makes pointwise measurements that are fundamentally Eulerian. Measurements have been made of the continuous gas phase velocity together with discrete phase attributes such as droplet size, droplet number count, and droplet velocity distribution at various axial stations downstream of the injector. Numerical calculations were performed under the exact inlet and boundary conditions as the experimental measurements. The computed gas phase velocity field showed good agreement with the test data. The agreement was found to be best at the stations close to the primary venturi of the swirler and to be reasonable at later stations. The unique contribution of this work is the formulation of a numerical PDPA scheme for comparing droplet data. The numerical PDPA scheme essentially converts the Lagrangian droplet phase data to the format of the experimental PDPA. Several sampling volumes (bins) were selected within the computational domain. The trajectories of various droplets passing through these volumes were monitored and appropriately integrated to obtain the distribution of the droplet characteristics in space. The calculated droplet count and mean droplet velocity distributions were compared with the measurements and showed very good agreement in the case of larger size droplets and fair agreement for smaller size droplets.
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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, no. 13 (July 8, 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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Chong, Cheng Tung, and Simone Hochgreb. "Spray Characteristics of an Internal-Mix Airblast Atomizer." Applied Mechanics and Materials 629 (October 2014): 125–30. http://dx.doi.org/10.4028/www.scientific.net/amm.629.125.
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Detailed characterisation of spray atomization of an injector is important for combustor design and modelling. In this paper, the effects of air/fuel mass ratio on the spray characteristics of an internal-mix airblast atomizer were examined. Distribution of the spatial mean droplet axial velocity and size were measured simultaneously using a phase Doppler anemometry (PDA). In general, small droplets are distributed at the center of the spray with maximum velocity. The droplet size increases with increasing radial distance from the spray centreline, but the drop velocity decreases to a minimum at the spray edge. Increasing the atomizing air/fuel mass ratio reduces fuel droplet size due to increased shear.
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Sahu, S., Y. Hardalupas, and A. M. K. P. Taylor. "Droplet–turbulence interaction in a confined polydispersed spray: effect of turbulence on droplet dispersion." Journal of Fluid Mechanics 794 (April 4, 2016): 267–309. http://dx.doi.org/10.1017/jfm.2016.169.
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The effect of entrained air turbulence on dispersion of droplets (with Stokes number based on the Kolmogorov time scale,$St_{{\it\eta}}$, of the order of 1) in a polydispersed spray is experimentally studied through simultaneous and planar measurements of droplet size, velocity and gas flow velocity (Hardalupaset al.,Exp. Fluids, vol. 49, 2010, pp. 417–434). The preferential accumulation of droplets at various measurement locations in the spray was examined by two independent methodsviz.counting droplets on images by dividing the image in to boxes of different sizes, and by estimating the radial distribution function (RDF). The dimension of droplet clusters (obtained by both approaches) was of the order of Kolmogorov’s length scale of the fluid flow, implying the significant influence of viscous scales of the fluid flow on cluster formation. The RDF of different size classes indicated an increase in cluster dimension for larger droplets (higher$St_{{\it\eta}}$). The length scales of droplet clusters increased towards the outer spray regions, where the gravitational influence on droplets is stronger compared to the central spray locations. The correlation between fluctuations of droplet concentration and droplet and gas velocities were estimated and found to be negative near the spray edge, while it was close to zero at other locations. The probability density function of slip between fluctuating droplet velocity and gas velocity ‘seen’ by the droplets signified presence of considerable instantaneous slip velocity, which is crucial for droplet–gas momentum exchange. In order to investigate different mechanisms of turbulence modulation of the carrier phase, the three correlation terms in the turbulent kinetic energy equation for particle-laden flows (Chen & Wood,Can. J. Chem. Engng, vol. 65, 1985, pp. 349–360) are evaluated conditional on droplet size classes. Based on the comparison of the correlation terms, it is recognized that although the interphase energy transfer due to fluctuations of droplet concentration is low compared to the energy exchange only due to droplet drag (the magnitude of which is controlled by average droplet mass loading), the former cannot be considered negligible, and should be accounted in two phase flow modelling.
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Tan, Xiao-Hua, Jian-Yi Liu, Xiao-Ping Li, Guang-Dong Zhang, and Chuan Tang. "A Fractal Model for the Maximum Droplet Diameter in Gas-Liquid Mist Flow." Mathematical Problems in Engineering 2013 (2013): 1–6. http://dx.doi.org/10.1155/2013/532638.
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Distribution characteristics of liquid droplet size are described using the fractal theory for liquid droplet size distribution in gas-liquid mist flow. Thereby, the fractal expression of the maximum droplet diameter is derived. The fractal model for maximum droplet diameter is obtained based on the internal relationship between maximum droplet diameter and the droplet fractal dimension, which is obtained by analyzing the balance between total droplet surface energy and total gas turbulent kinetic energy. Fractal model predictions of maximum droplet diameter agree with the experimental data. Maximum droplet diameter and droplet fractal dimension are both found to be related to the superficial velocity of gas and liquid. Maximum droplet diameter decreases with an increase in gas superficial velocity but increases with an increase in liquid superficial velocity. Droplet fractal dimension increases with an increase in gas superficial velocity but decreases with an increase in liquid superficial velocity. These are all consistent with the physical facts.
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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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Junping, Liu, Zhu Xingye, Yuan Shouqi, and Liu Xingfa. "Droplet Motion Model and Simulation of a Complete Fluidic Sprinkler." Transactions of the ASABE 61, no. 4 (2018): 1297–306. http://dx.doi.org/10.13031/trans.12639.
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Abstract. Simulation and experimental verification of the spray trajectory of a complete fluidic sprinkler was performed. Through further analysis of the forces moving droplets in the air and by exploring the relationship between the air drag coefficient and droplet trajectory, a droplet motion model was established. The velocity of a spray nozzle outlet is a gamma distribution, and the droplet deviation angle is a uniform distribution with a range of 0° to 360° when the sprinkler rotates uniformly for a full circle of spraying. The droplet size distribution in the spray area is approximately log-normal, the wind speed and direction follow a normal distribution, and the initial droplet angle is 27°. Based on a random simulation theory, the droplet trajectories were simulated using MATLAB software. The simulated results show that, compared to the tested value, the error between the simulated and measured values for the average droplet diameter decreased from 53% to 2% with increasing distance. The simulated values for droplet cumulative frequency and droplet speed were nearly the same as the tested value with only a small error. For both droplet distribution and kinetic energy, the relative error was less than 20%. Therefore, the stochastic simulation method can simulate the sprinkler droplet distribution characteristics. Keywords: Complete fluidic sprinkler, Droplet breakup mechanism, Droplet distribution, Droplet motion trajectory.
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Mohammadi, Moein, Jakub L. Nowak, Guus Bertens, Jan Moláček, Wojciech Kumala, and Szymon P. Malinowski. "Cloud microphysical measurements at a mountain observatory: comparison between shadowgraph imaging and phase Doppler interferometry." Atmospheric Measurement Techniques 15, no. 4 (February 23, 2022): 965–85. http://dx.doi.org/10.5194/amt-15-965-2022.
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Abstract. The microphysical properties of cloud droplets, such as droplet size distribution and droplet number concentration, were studied. A series of field experiments was performed in the summer of 2019 at the Umweltforschungsstation Schneefernerhaus (UFS), an environmental research station located just below the peak of the Zugspitze mountain in the German Alps. A VisiSize D30 manufactured by Oxford Laser Ltd., which is a shadowgraph imaging instrument, was utilized for the first time to measure the size and velocity of cloud droplets during this campaign. Furthermore, a phase Doppler interferometer (PDI) device, manufactured by Artium Tech. Inc., was simultaneously measuring cloud droplets. After applying modifications to the built-in software algorithms, the results from the two instruments show reasonable agreement regarding droplet sizing and velocimetry for droplet diameters larger than 13 µm. Moreover, discrepancies were observed concerning the droplet number concentration results, especially with smaller droplet sizes. Further investigation by applying appropriate filters to the data allowed the attribution of the discrepancies to two phenomena: the different optical performance of the sensors with regard to small droplets and high turbulent velocity fluctuations relative to the mean flow that result in an uncertain estimate of the volume of air passing through the PDI probe volume.
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Sahu, S., Y. Hardalupas, and A. M. K. P. Taylor. "Interaction of droplet dispersion and evaporation in a polydispersed spray." Journal of Fluid Mechanics 846 (May 3, 2018): 37–81. http://dx.doi.org/10.1017/jfm.2018.247.
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The interaction between droplet dispersion and evaporation in an acetone spray evaporating under ambient conditions is experimentally studied with an aim to understand the physics behind the spatial correlation between the local vapour mass fraction and droplets. The influence of gas-phase turbulence and droplet–gas slip velocity of such correlations is examined, while the focus is on the consequence of droplet clustering on collective evaporation of droplet clouds. Simultaneous and planar measurements of droplet size, velocity and number density, and vapour mass fraction around the droplets, were obtained by combining the interferometric laser imaging for droplet sizing and planar laser induced fluorescence techniques (Sahuet al.,Exp. Fluids, vol. 55, 1673, 2014b, pp. 1–21). Comparison with droplet measurements in a non-evaporating water spray under the same flow conditions showed that droplet evaporation leads to higher fluctuations of droplet number density and velocity relative to the respective mean values. While the mean droplet–gas slip velocity was found to be negligibly small, the vaporization Damköhler number ($Da_{v}$) was approximately ‘one’, which means the droplet evaporation time and the characteristic time scale of large eddies are of the same order. Thus, the influence of the convective effect on droplet evaporation is not expected to be significant in comparison to the instantaneous fluctuations of slip velocity, which refers to the direct effect of turbulence. An overall linearly increasing trend was observed in the scatter plot of the instantaneous values of droplet number density ($N$) and vapour mass fraction ($Y_{F}$). Accordingly, the correlation coefficient of fluctuations of vapour mass fraction and droplet number density ($R_{n\ast y}$) was relatively high (${\approx}0.5$) implying moderately high correlation. However, considerable spread of the$N$versus$Y_{F}$scatter plot along both coordinates demonstrated the influence on droplet evaporation due to turbulent droplet dispersion, which leads to droplet clustering. The presence of droplet clustering was confirmed by the measurement of spatial correlation coefficient of the fluctuations of droplet number density for different size classes ($R_{n\ast n}$) and the radial distribution function (RDF) of the droplets. Also, the tendency of the droplets to form clusters was higher for the acetone spray than the water spray, indicating that droplet evaporation promoted droplet grouping in the spray. The instantaneous group evaporation number ($G$) was evaluated from the measured length scale of droplet clusters (by the RDF) and the average droplet size and spacing in instantaneous clusters. The mean value of$G$suggests an internal group evaporation mode of the droplet clouds near the spray centre, while single droplet evaporation prevails near the spray boundary. However, the large fluctuations in the magnitude of instantaneous values of$G$at all measurement locations implied temporal variations in the mode of droplet cloud evaporation.
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HIROSE, Tomomi, Kotaro SATO, and Okitsugu FURUYA. "Influence of Outlet Velocity Distribution on Droplet Formation." Proceedings of the JSME annual meeting 2002.3 (2002): 259–60. http://dx.doi.org/10.1299/jsmemecjo.2002.3.0_259.
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Aihara, T., W. S. Fu, and Y. Suzuki. "Numerical Analysis of Heat and Mass Transfer From Horizontal Cylinders in Downward Flow of Air-Water Mist." Journal of Heat Transfer 112, no. 2 (May 1, 1990): 472–78. http://dx.doi.org/10.1115/1.2910402.
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A numerical analysis is made of heat and mass transfer from horizontal circular cylinders in a downward flow of air/water mist of polydisperse droplets, taking into account the far-upstream droplet size distribution and the blockage effect of the gas phase flow. The effects of the droplet size distribution, temperatures, and liquid-to-gas mass flow ratio upon the liquid film thickness and wall shear stress, velocity, and temperature of the air-water interface, two-phase Nusselt numbers, etc., are examined.
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Wang, Z. B., H. F. Bai, J. X. Xia, H. Q. Zhong, and Y. C. Li. "Theoretical Estimation of Maximum Ellipsoidal Magnitude of a Low-Viscosity Droplet in a Parallel Gas Stream." Journal of Mechanics 31, no. 6 (July 15, 2015): 727–32. http://dx.doi.org/10.1017/jmech.2015.26.
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ABSTRACTMaximum ellipsoidal magnitude of the droplet is an important basic parameter for calculating drag force, droplets axial-velocity and dispersed-phase pressure gradient in an annular-mist pipe flow. An analytical correlation to predict the maximum ellipsoidal magnitude of a low-viscosity droplet in a parallel gas stream based on energy conservation and volume conservation. Stagnant pressure distribution on droplet surface is revised from Flachsbart's formula. The proposed correlation has clear physical meaning and easy to use. The correlation captures the deformation mechanism with an average absolute percent error of 9.53%. The effect of stagnant pressure distribution on the proposed correlation's accuracy is discussed.
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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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Shukla, Isha, Nicolas Kofman, Gioele Balestra, Lailai Zhu, and François Gallaire. "Film thickness distribution in gravity-driven pancake-shaped droplets rising in a Hele-Shaw cell." Journal of Fluid Mechanics 874 (July 15, 2019): 1021–40. http://dx.doi.org/10.1017/jfm.2019.453.
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We study here experimentally, numerically and using a lubrication approach, the shape, velocity and lubrication film thickness distribution of a droplet rising in a vertical Hele-Shaw cell. The droplet is surrounded by a stationary immiscible fluid and moves purely due to buoyancy. A low density difference between the two media helps to operate in a regime with capillary number $Ca$ lying between $0.03$ and $0.35$, where $Ca=\unicode[STIX]{x1D707}_{o}U_{d}/\unicode[STIX]{x1D6FE}$ is built with the surrounding oil viscosity $\unicode[STIX]{x1D707}_{o}$, the droplet velocity $U_{d}$ and surface tension $\unicode[STIX]{x1D6FE}$. The experimental data show that in this regime the droplet velocity is not influenced by the thickness of the thin lubricating film and the dynamic meniscus. For iso-viscous cases, experimental and three-dimensional numerical results of the film thickness distribution agree well with each other. The mean film thickness is well captured by the Aussillous & Quéré (Phys. Fluids, vol. 12 (10), 2000, pp. 2367–2371) model with fitting parameters. The droplet also exhibits the ‘catamaran’ shape that has been identified experimentally for a pressure-driven counterpart (Huerre et al., Phys. Rev. Lett., vol. 115 (6), 2015, 064501). This pattern has been rationalized using a two-dimensional lubrication equation. In particular, we show that this peculiar film thickness distribution is intrinsically related to the anisotropy of the fluxes induced by the droplet’s motion.
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Paoli, Roberto, and Karim Shariff. "Turbulent Condensation of Droplets: Direct Simulation and a Stochastic Model." Journal of the Atmospheric Sciences 66, no. 3 (March 1, 2009): 723–40. http://dx.doi.org/10.1175/2008jas2734.1.
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Abstract The effect of turbulent mixing on droplet condensation is studied via direct numerical simulations of a population of droplets in a periodic box of homogeneous isotropic turbulence. Each droplet is tracked as a fluid particle whose radius grows by condensation of water vapor. Forcing of the small wavenumbers is used to sustain velocity, vapor, and temperature fluctuations. Temperature and vapor fluctuations lead to supersaturation fluctuations, which are responsible for broadening the droplet size distribution in qualitative agreement with in situ measurements. A model for the condensation of a population of cloud droplets in a homogeneous turbulent flow is presented. The model consists of a set of Langevin (stochastic) equations for the droplet area, supersaturation, and temperature surrounding the droplets. These equations yield corresponding ordinary differential equations for various moments and correlations. The statistics predicted by the model, for instance, the droplet area–supersaturation correlation, reproduce the simulations well.
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Perrin, Vincent E., and Harmen J. J. Jonker. "Lagrangian Droplet Dynamics in the Subsiding Shell of a Cloud Using Direct Numerical Simulations." Journal of the Atmospheric Sciences 72, no. 10 (October 1, 2015): 4015–28. http://dx.doi.org/10.1175/jas-d-15-0045.1.
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Abstract This study investigates the droplet dynamics at the lateral cloud–environment interface in shallow cumulus clouds. A mixing layer is used to study a small part of the cloud edge using direct numerical simulation combined with a Lagrangian particle tracking and collision algorithm. The effect of evaporation, gravity, coalescence, and the initial droplet size distribution on the intensity of the mixing layer and the evolution of the droplet size distribution is studied. Mixing of the droplets with environmental air induces evaporative cooling, which results in a very characteristic subsiding shell. As a consequence, stronger horizontal velocity gradients are found in the mixing layer, which induces more mixing and evaporation. A broadening of the droplet size distribution is observed as a result of evaporation and coalescence. Gravity acting on the droplets allows droplets in cloudy filaments detrained from the cloud to sediment and remain longer in the unsaturated environment. While this effect of gravity did not have a significant impact in this case on the mean evolution of the mixing layer, it does contribute to the broadening of the droplet size distribution and thereby significantly increases the collision rate. Although more but smaller droplets result in more evaporative cooling, more droplets also increase small-scale fluctuations and the production of turbulent dissipation. For the smallest droplets considered with a radius of 10 μm, the authors found that, although a more pronounced buoyancy dip was present, the increase in dissipation rate actually led to a decrease in the turbulent intensity of the mixing layer. Extrapolation of the results to realistic clouds is discussed.
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Zhu, Zhongrui, Delan Zhu, and Maosheng Ge. "The Spatial Variation Mechanism of Size, Velocity, and the Landing Angle of Throughfall Droplets under Maize Canopy." Water 13, no. 15 (July 30, 2021): 2083. http://dx.doi.org/10.3390/w13152083.
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Larger diameter and velocity and smaller landing angle of sprinkler irrigation droplets are more likely to cause soil splash and erosion. However, the mechanism of crop canopy influence on the physical parameters of sprinkler droplets is unknown. In this study, with the landing angle of sprinkler irrigation droplets as the independent variable and maize plants (Zea mays L.) as the research object, an indoor sprinkler irrigation experiment was carried out. The effects of maize canopy and variation in sprinkler irrigation droplets landing angle on the value and spatial distribution pattern of size, the velocity, and the landing angle of throughfall droplets was analyzed. In addition, the spatial variation patterns of throughfall droplets size, velocities’ distribution, and individual droplet’s speed, kinetic energy were also explored. The results showed that maize canopy and the decreasing of the sprinkler irrigation droplet landing angle had a positive and obvious effect on reducing the size and velocity of penetrating rain droplets. However, the throughfall droplets’ landing angles were only small variations. When the landing angle of sprinkler irrigation droplets was >45°, the spatial distribution of throughfall droplets size and velocity corresponded well with the canopy structure and leaf projection area of maize, i.e., the further away from the maize stalk, the larger the size and velocity of throughfall droplets. Nevertheless, if the landing angle of sprinkler irrigation droplets was <45°, the spatial distribution mentioned above was mainly affected by droplets landing angle. The spatial variation of throughfall droplets’ size and velocities at different measurement points was attributed to the change of the larger droplets’ volume proportion and the equivalent velocity. Although the maize leaves had a certain degree of perturbation effect on the velocities and kinetic energy of the larger kinetic energy droplets, the flight path of these drops did not alter significantly. The results of this research will be of practical value in guiding the development of a new sprayer and the optimum selection of sprinkler heads.
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Nishandar, Sanika Ravindra, Yucheng He, Marko Princevac, and Rufus D. Edwards. "Fate of Exhaled Droplets From Breathing and Coughing in Supermarket Checkouts and Passenger Cars." Environmental Health Insights 17 (January 2023): 117863022211482. http://dx.doi.org/10.1177/11786302221148274.
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The global pandemic of COVID-19 has highlighted the importance of understanding the role that exhaled droplets play in virus transmission in community settings. Computational Fluid Dynamics (CFD) enables systematic examination of roles the exhaled droplets play in the spread of SARS-CoV-2 in indoor environments. This analysis uses published exhaled droplet size distributions combined with terminal aerosol droplet size based on measured peak concentrations for SARS-CoV-2 RNA in aerosols to simulate exhaled droplet dispersion, evaporation, and deposition in a supermarket checkout area and rideshare car where close proximity with other individuals is common. Using air inlet velocity of 2 m/s in the passenger car and ASHRAE recommendations for ventilation and comfort in the supermarket, simulations demonstrate that exhaled droplets <20 μm that contain the majority of viral RNA evaporated leaving residual droplet nuclei that remain aerosolized in the air. Subsequently ~ 70% of these droplet nuclei deposited in the supermarket and the car with the reminder vented from the space. The maximum surface deposition of droplet nuclei/m2 for speaking and coughing were 2 and 819, 18 and 1387 for supermarket and car respectively. Approximately 15% of the total exhaled droplets (aerodynamic diameters 20-700 µm) were deposited on surfaces in close proximity to the individual. Due to the non-linear distribution of viral RNA across droplet sizes, however, these larger exhaled droplets that deposit on surfaces have low viral content. Maximum surface deposition of viral RNA was 70 and 1.7 × 103 virions/m2 for speaking and 2.3 × 104 and 9.3 × 104 virions/m2 for coughing in the supermarket and car respectively while the initial airborne concentration of viral RNA was 7 × 106 copies per ml. Integrating the droplet size distributions with viral load distributions, this study helps explain the apparent importance of inhalation exposures compared to surface contact observed in the pandemic.
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Song, Yuchao, Yafei Zhang, and Hongtao Gao. "Numerical Analysis of the Free-Falling Process of a Water Droplet at Different Temperatures." Processes 11, no. 1 (January 13, 2023): 258. http://dx.doi.org/10.3390/pr11010258.
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The collision behavior and ice formation of a water droplet are affected by its falling process. In this paper, the two-phase flow of air and a water droplet at a specific temperature is adopted to investigate the processes of falling and freezing of a single water droplet. To track the air–water droplet interface and the temperature distribution, the level-set method and the non-isothermal flow coupling method are used, and the freezing model is added into the water’s control equations. The numerical results indicated that with the initial temperature at 283.15 K and the spherical shape, the water droplet changes to the shape of a straw hat at 293.15 K and a drum at 293.15 K but an oval face in freezing temperatures at 0.10 s. There is an obvious drop in the downward velocity when the water droplet falls in mild temperatures at 0.09 s. The downward velocity of the water droplet in air at sub-zero temperatures has a continuous increase during the time span from 0 s to 0.10 s. There is also an obvious difference when the water droplet impinges on the solid bottom. Lastly, the freezing of sessile water droplets attached on the horizontal surface is helpful to reveal the unique phase change process of water droplets in cold air.
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Sharma, Nikhil, William D. Bachalo, and Avinash Kumar Agarwal. "Spray droplet size distribution and droplet velocity measurements in a firing optical engine." Physics of Fluids 32, no. 2 (February 1, 2020): 023304. http://dx.doi.org/10.1063/1.5126498.
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Krištof, Ondřej, Pavel Bulejko, and Tomáš Svěrák. "Experimental Study on Spray Breakup in Turbulent Atomization Using a Spiral Nozzle." Processes 7, no. 12 (December 3, 2019): 911. http://dx.doi.org/10.3390/pr7120911.
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Spiral nozzles are widely used in wet scrubbers to form an appropriate spray pattern to capture the polluting gas/particulate matterwith the highest possible efficiency. Despite this fact, and a fact that it is a nozzle with a very atypical spray pattern (a full cone consisting of three concentric hollow cones), very limited amount of studies have been done so far on characterization of this type of nozzle. This work reports preliminary results on the spray characteristics of a spiral nozzle used for gas absorption processes. First, we experimentally measured the pressure impact footprint of the spray generated. Then effective spray angles were evaluated from the photographs of the spray and using the pressure impact footprint records via Archimedean spiral equation. Using the classical photography, areas of primary and secondary atomization were determined together with the droplet size distribution, which were further approximated using selected distribution functions. Radial and tangential spray velocity of droplets were assessed using the laser Doppler anemometry. The results show atypical behavior compared to different types of nozzles. In the investigated measurement range, the droplet-size distribution showed higher droplet diameters (about 1 mm) compared to, for example, air assisted atomizers. It was similar for the radial velocity, which was conversely lower (max velocity of about 8 m/s) compared to, for example, effervescent atomizers, which can produce droplets with a velocity of tens to hundreds m/s. On the contrary, spray angle ranged from 58° and 111° for the inner small and large cone, respectively, to 152° for the upper cone, and in the measured range was independent of the inlet pressure of liquid at the nozzle orifice.
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Glahn, A., M. F. Blair, K. L. Allard, S. Busam, O. Scha¨fer, and S. Wittig. "Disintegration of Oil Films Emerging From Radial Holes in a Rotating Cylinder." Journal of Engineering for Gas Turbines and Power 125, no. 4 (October 1, 2003): 1011–20. http://dx.doi.org/10.1115/1.1586311.
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A fundamental study has been performed to examine the disintegration of oil films emerging from radial holes in a rotating hollow cylinder. The configuration investigated is an abstraction of one of the droplet generation sources in an aeroengine bearing compartment; similar configurations may also occur inside gearboxes. The paper aims to contribute to both the determination of directly applicable droplet characteristics and the establishment of a database that can be used for the development of droplet generation models. Similar to a prior paper on droplet generation processes at the rim of a rotating disk (Glahn, A. et al., 2000, “Droplet Generation by Disintegration of Oil Films at the Rim of a Rotating Disk,” ASME Paper No. 2000-GT-0279.) the near-term objectives of the study are (i) to determine droplet sizes under relevant aeroengine bearing compartment operating conditions, and (ii) to measure individual droplet diameter/velocity relationships. The long-term objective is to incorporate this information into advanced CFD-based design tools. Therefore, special emphasis has been directed towards a correlation of test results that enables determination of boundary conditions for a two-phase (oil droplets/air) simulation of lubrication system components. Based on the results of the present paper, droplet flow boundary conditions in terms of mean diameter, standard deviation of the diameter distribution, starting velocity, and flow angle are available for oil droplets generated by disintegration of oil films emerging from rotating radial holes and rotating disks.
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Wang, H. Y., V. G. McDonell, and S. Samuelsen. "Influence of Hardware Design on the Flow Field Structures and the Patterns of Droplet Dispersion: Part I—Mean Quantities." Journal of Engineering for Gas Turbines and Power 117, no. 2 (April 1, 1995): 282–89. http://dx.doi.org/10.1115/1.2814092.
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In a gas turbine engine combustor, performance is likely tied to the spatial distribution of the fuel injected into the dome. The GE/SNECMA CFM56 combustor swirl cup is one example of a design established to provide a uniform presentation of droplets to the dome. The present study is part of a series to detail the dispersion of droplets in practical hardware, and to assess the effect of isolated parameters on the continuous- and dispersed-phase distributions. In this study, the influence of the swirling air outlet geometry is evaluated relative to the effect on the flow field structures and the patterns of droplet dispersion. This is accomplished by comparing the continuous-phase (air in the presence of a spray) and dispersed-phase (droplets) behavior downstream of the swirl cup assembly outfitted with two different conical expansions (“flares”). One features a narrow expansion angle, the other possesses a wide expansion angle. Two-component phase-Doppler interferometry was employed to provide the information of droplet size and velocity components as well as continuous-phase velocity components. Photographs of light scattered by droplets from a laser sheet were used for the study of flow field structures. This study reveals that (1) the air stream issued from the narrow flare remains close to the centerline and expands gradually downstream while the air stream issued from the wide flare expands immediately downstream of the swirl cup, and (2) the narrow flare provides weaker droplet dispersion, slower decay of droplet velocities, and finer droplet sizes compared to the wide flare. The results demonstrate that a relatively modest change in flare geometry can create a significant change in the structure of both the continuous and dispersed phases.
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Achury, Javier, and Wolfgang Polifke. "Modulation of spray droplet number density and size distribution by an acoustic field." Journal of Computational Multiphase Flows 9, no. 1 (February 12, 2017): 32–46. http://dx.doi.org/10.1177/1757482x17690751.
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Multiple interactions may occur when a poly-disperse spray is exposed to an acoustic field. In the context of spray combustion instabilities, acoustic agglomeration, the formation of a droplet number density wave and the modulation of the droplet size distribution are interesting effects. A droplet number density wave, i.e. preferential concentration of droplets in space, may result from size-dependent, one-way momentum coupling between the acoustic field and the spray. The modulation of the droplet size distribution, which has been evidenced in the experimental work of Gurubaran and Sujith (AIAA 2008-1046), is thus a consequence of the droplet number density wave formation. In the present work, the mechanisms that produce these effects are simulated and analyzed in depth by means of computational fluid dynamics. The spray is modeled with both Lagrangian (particles mass-point approach) and Eulerian (continuous phase approach) descriptions. The particular Eulerian method used is a variant of the presumed density function method of moments, which allows to account for the effects of poly-dispersity, in particular the size-dependence of particle velocity. Both the Lagrangian and Eulerian models are validated against experimental data for spray dynamics and spray response to an acoustic field.
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Bougiatioti, Aikaterini, Athanasios Nenes, Jack J. Lin, Charles A. Brock, Joost A. de Gouw, Jin Liao, Ann M. Middlebrook, and André Welti. "Drivers of cloud droplet number variability in the summertime in the southeastern United States." Atmospheric Chemistry and Physics 20, no. 20 (October 27, 2020): 12163–76. http://dx.doi.org/10.5194/acp-20-12163-2020.
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Abstract. Here we analyze regional-scale data collected on board the NOAA WP-3D aircraft during the 2013 Southeast Nexus (SENEX) campaign to study the aerosol–cloud droplet link and quantify the sensitivity of droplet number to aerosol number, chemical composition, and vertical velocity. For this, the observed aerosol size distributions, chemical composition, and vertical-velocity distribution are introduced into a state-of-the-art cloud droplet parameterization to show that cloud maximum supersaturations in the region range from 0.02 % to 0.52 %, with an average of 0.14±0.05 %. Based on these low values of supersaturation, the majority of activated droplets correspond to particles with a dry diameter of 90 nm and above. An important finding is that the standard deviation of the vertical velocity (σw) exhibits considerable diurnal variability (ranging from 0.16 m s−1 during nighttime to over 1.2 m s−1 during day), and it tends to covary with total aerosol number (Na). This σw–Na covariance amplifies the predicted response in cloud droplet number (Nd) to Na increases by 3 to 5 times compared to expectations based on Na changes alone. This amplified response is important given that droplet formation is often velocity-limited and therefore should normally be insensitive to aerosol changes. We also find that Nd cannot exceed a characteristic concentration that depends solely on σw. Correct consideration of σw and its covariance with time and Na is important for fully understanding aerosol–cloud interactions and the magnitude of the aerosol indirect effect. Given that model assessments of aerosol–cloud–climate interactions do not routinely evaluate for overall turbulence or its covariance with other parameters, datasets and analyses such as the one presented here are of the highest priority to address unresolved sources of hydrometeor variability, bias, and the response of droplet number to aerosol perturbations.
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Prikhodko, V. G., V. N. Yarygin, and I. V. Yarygin. "Interaction of a liquid jet with a co-current gas flow inside the nozzle and under ejection into vacuum." Journal of Physics: Conference Series 2119, no. 1 (December 1, 2021): 012112. http://dx.doi.org/10.1088/1742-6596/2119/1/012112.
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Abstract The structure of a gas-droplet flow arising under gas outflow with liquid jet injected into it from a supersonic nozzle into vacuum is studied experimentally. Possibility of the flow structure control in order to obtain droplets of a certain size, composition, and velocity, is considered. The liquid was injected into the co-current gas flow in the prechamber of the supersonic nozzle and then flowed out into the vacuum chamber in the form of a gas-droplet jet. Using the developed technique of droplet deposition on paper substrates, the effect of the Reynolds number of the gas and the pressure in the vacuum chamber on the angular distribution of droplet phase behind the nozzle exit is investigated.
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Qu, Yong Lei, Shi Bu, and Bo Wan. "A 3D Numerical Investigation on Droplets Distribution in a Wave-Plate Separator." Advanced Materials Research 842 (November 2013): 522–29. http://dx.doi.org/10.4028/www.scientific.net/amr.842.522.
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The gas-liquid flow in a wave-plate separator is extremely complex due to its three-dimensional characteristic. Numerical simulation accomplished by former investigators using two-dimensional model may be appropriate for the iteration of pressure drop, but they were far from accurate in prediction of removal efficiency. To fill the gap, a three dimensional geometrical model of wave-plate separator is set up in this paper, RNG k-ε model is employed to compute the gas phase flow field, and the droplet trajectories were predicted applying the Lagrangian method. The turbulent dispersion of droplets were simulated by discrete random walk model. Using the assumption of a constant liquid loading of gas flow, simulation were accomplished for six different inlet velocities and two different droplet sizes. The influence pattern of gravity together with gas velocity on droplets distribution and the overall removal efficiencies were obtained.
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Jing, Linlong, and Xinhua Wei. "Spray Deposition and Distribution on Rice as Affected by a Boom Sprayer with a Canopy-Opening Device." Agriculture 13, no. 1 (December 29, 2022): 94. http://dx.doi.org/10.3390/agriculture13010094.
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In China, rice growers predominantly use boom sprayers. However, boom sprayers have several drawbacks related to poor penetration in the middle and late stages of rice growth. Several studies have shown that the use of the canopy-opening device can improve droplet deposition in the middle and under layers of rice. Some growers doubt the efficacy of canopy-opening boom sprayers, whereas others have questions about their use. This study aimed to address both doubts and questions by evaluating the effect of spraying rice using a canopy-opening device and a canopy-opening divider combination device. The tested rice variety was “Longliangyou 2010”. Three different boom sprayers were evaluated for this purpose: (1) a boom sprayer with a canopy-opening device, (2) a boom sprayer with a canopy-opening divider combination device, and (3) a traditional boom sprayer. The effects of the position of the canopy-opening device and the spraying velocity on the deposition of droplets were considered. The experiments showed that the droplet coverage was significantly affected by boom sprayers, the position of the canopy-opening device, the spraying velocity, and the interaction of the position of the canopy-opening device and the spraying velocity. Under the spraying distance of 60 cm from the rice root and the spraying velocity of 1.2 m s−1, the spraying coverage of the paraxial surface of the whole canopy was higher than that of other treatment conditions when the canopy opening device was used. The positive spraying coverage rates of the upper, middle and lower layers were 95.18%, 88.41% and 94.99%, respectively. Compared with the traditional boom sprayer, the use of the canopy-opening device increased the average droplet coverage on the adaxial surface canopy by more than 72.91% and the average droplet coverage on the abaxial surface canopy by more than 6.88%.
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Hoffmann, Sven, Simon Holz, Rainer Koch, and Hans-Jörg Bauer. "Euler–Lagrangian simulation of the fuel spray of a planar prefilming airblast atomizer." CEAS Aeronautical Journal 12, no. 2 (February 21, 2021): 245–59. http://dx.doi.org/10.1007/s13272-021-00493-y.
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AbstractThe pollutant emissions of aircraft engines are strongly affected by the fuel injection into the combustion chamber. Hence, the precise description of the fuel spray is required in order to predict these emissions more reliably. The characteristics of a spray is determined during the atomization process, especially during primary breakup in the vicinity of the atomizer nozzle. Currently, Euler-Lagrangian approaches are used to predict the droplet trajectories in combustor simulations along with reaction and pollutant formation models. To be able to reliably predict pollutant emissions in the future, well-defined starting conditions of the liquid fuel droplets close to the atomizer nozzle are necessary. In the present work, Euler-Lagrangian simulations of a generic airblast atomizer are presented. The starting conditions of the droplets are varied in the simulations by means of a primary breakup model, which takes into account the local gas velocity when predicting the droplet diameter. The objective of this work is to determine the optimal parameters of the probability density functions for the starting position and the starting velocity of the droplets. Spray properties observed in the simulations are used to qualitatively evaluate the major effects of the distribution parameters on the spray and the suitability of the primary breakup model being applied. Hence, the spatial distribution of an experimental spray can be reproduced using a statistical model for the droplet starting conditions.
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Fan, Shuangshuang, Ying Wang, Kun Yao, Jiakui Shi, Jun Han, and Jie Wan. "Distribution Characteristics of High Wetness Loss Area in the Last Two Stages of Steam Turbine under Varying Conditions." Energies 15, no. 7 (March 30, 2022): 2527. http://dx.doi.org/10.3390/en15072527.
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Wetness loss of a steam turbine seriously affects the security of the unit when operating in deep peak regulation. To obtain the distribution characteristics of the high wetness loss area under different working conditions, especially low-load conditions, the last two stages of the low-pressure cylinder (LPC) of a 600 MW steam turbine were simulated using the non-equilibrium condensation model proposed in this study. The nucleation rate distribution, supercooling degree, and steam velocity droplet were analyzed. Consequently, the diameter distribution of coarse water droplets under 100%, 50%, 40%, 30%, and 20% THA conditions and the distribution of the thermodynamic loss and water droplet resistance loss were obtained. Thermodynamic loss mainly occurred at the front end of second-stage stator blades and trailing end of the last-stage stator blades. The water droplet resistance loss mainly occurred at 40% of the blade height and at the tip of the last-stage stator blades. Moreover, with a reduction in the unit load, the thermodynamic loss continued to decrease, but the water droplet resistance loss continued to increase.
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Vadlamudi, Gautham, S. K. Thirumalaikumaran, Dipshikha Chakravortty, Abhishek Saha, and Saptarshi Basu. "Penetration and aerosolization of cough droplet spray through face masks: A unique pathway of transmission of infection." Physics of Fluids 34, no. 5 (May 2022): 052108. http://dx.doi.org/10.1063/5.0093297.
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The advent of the COVID-19 pandemic has necessitated the use of face masks, making them an integral part of the daily routine. Face masks occlude the infectious droplets during any respiratory event contributing to source control. In the current study, spray impingement experiments were conducted on porous surfaces like masks having a different porosity, pore size, and thickness. The spray mimics actual cough or a mild sneeze with respect to the droplet size distribution (20–500 [Formula: see text]) and velocity scale (0–14 [Formula: see text]), which makes the experimental findings physiologically realistic. The penetration dynamics through the mask showed that droplets of all sizes beyond a critical velocity penetrate through the mask fabric and atomize into daughter droplets in the aerosolization range, leading to harmful effects due to the extended airborne lifetime of aerosols. By incorporating spray characteristics along with surface tension and viscous dissipation of the fluid passing through the mask, multi-step penetration criteria have been formulated. The daughter droplet size and velocity distribution after atomizing through multi-layered masks and its effects have been discussed. Moreover, the virus-emulating particle-laden surrogate respiratory droplets are used in impingement experiments to study the filtration and entrapment of virus-like nanoparticles in the mask. Furthermore, the efficacy of the mask from the perspective of a susceptible person has been investigated.
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Markt, David, Ashish Pathak, Mehdi Raessi, Seong-Young Lee, and Roberto Torelli. "Computational characterization of the secondary droplets formed during the impingement of a train of ethanol drops." International Journal of Engine Research 21, no. 2 (October 10, 2019): 248–62. http://dx.doi.org/10.1177/1468087419879623.
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This article uniquely characterizes the secondary droplets formed during the impingement of a train of ethanol drops, using three-dimensional direct numerical simulations performed under conditions studied experimentally by Yarin and Weiss. Our numerical results have been previously validated against experimental data demonstrating the ability to accurately capture the splashing dynamics. In this work, the predictive ability of the model is leveraged to gain further insight into secondary droplet formation. We present a robust post-processing algorithm, which scrutinizes the liquid volume fraction field in the volume-of-fluid method and quantifies the number, volume and velocity of secondary droplets. The high-resolution computational simulations enable secondary droplet characterization within close proximity of the impingement point at small length and time scales, which is extremely challenging to achieve experimentally. By studying the temporal evolution of secondary droplet formation, direct connections are made between liquid structures seen in the simulation and the instantaneous distribution of secondary droplets, leading to detailed insight into the instability-driven breakup process of lamellae. Time-averaged secondary droplet characteristics are also studied to describe the global distribution of secondary droplets. Such analysis is vital to understanding fuel drop impingement in direct injection engines, facilitating the development of highly accurate spray–wall interaction models for use in Lagrangian solvers.
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Eroglu, H., and N. Chigier. "Initial Drop Size and Velocity Distributions for Airblast Coaxial Atomizers." Journal of Fluids Engineering 113, no. 3 (September 1, 1991): 453–59. http://dx.doi.org/10.1115/1.2909517.
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Initial drop size and velocity distributions, after complete disintegration of coaxial liquid jets, were determined by phase Doppler measurements. The measured radial distributions of Sauter mean diameter (SMD) were compared with the photographs of the disintegrating liquid jet. The SMD distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet. The results showed that SMD increases with increasing liquid supply pressure as well as with decreasing air supply pressure. The axial measurement stations were determined from the photographs of the coaxial liquid jet at very short distances (1–2 mm) downstream of the observed break-up locations. The droplets accelerated at these regions under the influence of the air velocity. Smaller droplets were found to reach higher velocities because of their larger drag-to-momentum ratio. In general, minimum droplet mean velocities were found at the center, and the maximum velocities were near the spray boundary. Size velocity correlations show that the velocity of larger drops did not change with drop size. Drop rms velocity distributions have double peaks whose radial positions coincide with the maximum mean velocity gradients.
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Jin, Yi, Kanghong Yao, Xiaomin He, Kai Zhang, and Yunbiao Wang. "Experimental Study of the Effect of the Expansion Segment Geometry on the Atomization of a Plain-Jet Airblast Atomizer." International Journal of Aerospace Engineering 2021 (April 23, 2021): 1–15. http://dx.doi.org/10.1155/2021/6623340.
Full textAbstract:
In this paper, the idea of adding an expansion segment over traditional airblast atomizer is proposed to improve the spray performance. According to the systematic experiments, the Sauter mean diameter, the droplet size distribution, and the droplet axial mean velocity were obtained to evaluate the spray performance. The correlations between spray performance and four geometrical parameters of the expansion segment which include the length, the angle, the throat area, and position of liquid jet are considered. The atomizer operates at atmospheric pressure and temperature, and the air liquid ratio range is from 0.48 to 2.85. The data of the results were measured by Phase Doppler Particle Analyzer. The results show that more uniform droplet size distribution can be achieved with the addition of expansion segment, and the droplet size distribution factor q of the case adding the expansion segment is 52.8% bigger than that of the case with no expansion segment. q increases as the length and angle of expansion segment increase. The Sauter mean diameter can be reduced by either reducing the length or angle of expansion segment. As for droplet velocity, it is determined that the droplet velocity increases along the radial direction, which is noteworthy because opposite trend is reported for traditional plain-jet atomizers. With an increase of the length, angle, and throat area of the expansion segment, the droplet axial velocity decays.
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Xiao, Yuan, Huanhuan Liu, Song Shen, and Pengcheng Yang. "Modelling of Droplet Deposition Shape on Fabric Surface using Spray Printing." AATCC Journal of Research 7, no. 1 (January 1, 2020): 37–45. http://dx.doi.org/10.14504/ajr.7.1.5.
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A droplet-impacted fabric surface deposition process was established based on the two-phase volume of fluid (VOF) computing model. This study was important because implementation of drop-on-demand 3D printing used for forming flexible conductive lines on fabric depends on understanding the droplet deposition mechanism. The interaction of droplets and the fabric substrate, as well as the penetration process, were simulated. The distribution of pressure and velocity, and the influence of surface tension and viscosity, in the droplet deposition process were also studied. The simulation and confirmatory experimental results show that the internal pressure gradient in the liquid was the main reason for the droplet spreading, penetration, and bubble formation. These research results lay a theoretical foundation for droplet spray printing of conductive lines on fabric surfaces.
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Tanaka, T., M. Sato, M. Kobayashi, and H. Shirakawa. "Development of a Novel Advanced Spray Technology Based on Investigation of Droplet Energy and Pattern Damage." Solid State Phenomena 187 (April 2012): 153–56. http://dx.doi.org/10.4028/www.scientific.net/ssp.187.153.
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A novel advanced spray technology, in which droplet size and velocity are accurately and tightly controlled, has been developed to realize the damage-free cleaning for next generation device manufacturing. The influence of droplet characteristics on pattern collapse/damage was quantitatively investigated using this technology. It was shown that the amount of damage was correlated to the droplet energy density on the wafer. The mechanism of pattern damage generated by the conventional dual fluid spray was revealed by the damage threshold curve, which was obtained from the theoretical consideration. Finally higher particle removal efficiency without any pattern damage was achieved by controlling the distribution of effective droplets for cleaning.
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Albert, R., and P. V. Farrell. "Droplet Sizing Using the Shifrin Inversion." Journal of Fluids Engineering 116, no. 2 (June 1, 1994): 357–62. http://dx.doi.org/10.1115/1.2910281.
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A method for measuring droplet size distributions was investigated with an emphasis on limitations related to measurements in real spray environments. The method stores a photographic image of a plane of droplets within a spray and is capable of evaluating particle size distributions within the spray, one small region at a time. The method complements droplet velocity measurements made using Particle Image Velocimetry. In a typical experiment, a plane of the spray was illuminated by a laser light sheet and photographed. After processing, a small laser beam scanned the film and a diffraction pattern was generated for each region illuminated by the small laser. The diffraction pattern was inverted using a Shifrin inversion to solve for the particle size distribution within the illuminated region. In this paper we will discuss some of the limitations of this method and indicate one approach which seems to allow for improved inversions using data signal processing.
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Guo, Huiqian, Jing Wang, Jiangbo Wu, and Xiaoze Du. "Study on Spray Evaporation Treatment of Desulfurization Wastewater." Coatings 11, no. 4 (April 4, 2021): 418. http://dx.doi.org/10.3390/coatings11040418.
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Limestone-gypsum wet flue gas desulfurization (WFGD) often produces a certain amount of wastewater with complex water quality and heavy metal pollution which should be treated properly before release. Spaying the desulfurization wastewater into flue duct and using exhausted flue gas heat for evaporation is a promising and economical technology for achieving zero wastewater discharge in thermal power plant. To enable a more in-depth understanding on evaporation of FGD wastewater spray, a visual wind tunnel test rig based on the atomized droplet laser measuring system was built to reveal the impact factors on droplet thermal-fluid behavior. The dominant impact factors such as compressed air pressure and flow rate in air-blast spray nozzle, hot air temperature and velocity in the evaporation tunnel were analyzed to discuss the droplet size distribution and evaporation performance through alternating operate condition. A discrete mathematical model that combines both Eulerian and Lagrangian framework was established to validate the experiment result. It is concluded that introducing high pressure compressed air into the nozzle can contribute to the dispersion of droplets and enhance the evaporation rate. Proper flow rate in spray nozzle is required to avoid incomplete droplets evaporation. Air temperature and velocity in the evaporation tunnel apply positive impact on droplet size distribution and evaporation performance. Numerical simulation results of both dominant factors impact on evaporation behavior and total evaporation rate showed consistency with the experimental outcome.