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1
Heyn, Christian, and Stefan Feddersen. "Modeling of Al and Ga Droplet Nucleation during Droplet Epitaxy or Droplet Etching." Nanomaterials 11, no. 2 (February 12, 2021): 468. http://dx.doi.org/10.3390/nano11020468.
Повний текст джерелаАнотація:
The temperature dependent density of Al and Ga droplets deposited on AlGaAs with molecular beam epitaxy is studied theoretically. Such droplets are important for applications in quantum information technology and can be functionalized e.g., by droplet epitaxy or droplet etching for the self-assembled generation of quantum emitters. After an estimation based on a scaling analysis, the droplet densities are simulated using first a mean-field rate model and second a kinetic Monte Carlo (KMC) simulation basing on an atomistic representation of the mobile adatoms. The modeling of droplet nucleation with a very high surface activity of the adatoms and ultra-low droplet densities down to 5 × 106 cm−2 is highly demanding in particular for the KMC simulation. Both models consider two material related model parameters, the energy barrier ES for surface diffusion of free adatoms and the energy barrier EE for escape of atoms from droplets. The rate model quantitatively reproduces the droplet densities with ES = 0.19 eV, EE = 1.71 eV for Al droplets and ES = 0.115 eV for Ga droplets. For Ga, the values of EE are temperature dependent indicating the relevance of additional processes. Interestingly, the critical nucleus size depends on deposition time, which conflicts with the assumptions of the scaling model. Using a multiscale KMC algorithm to substantially shorten the computation times, Al droplets up to 460 °C on a 7500 × 7500 simulation field and Ga droplets up to 550 °C are simulated. The results show a very good agreement with the experiments using ES = 0.19 eV, EE = 1.44 eV for Al, and ES = 0.115 eV, EE = 1.24 eV (T≤ 300 °C) or EE = 1.24 + 0.06 (T[°C] − 300)/100 eV (T>300 °C) for Ga. The deviating EE is attributed to a re-nucleation effect that is not considered in the mean-field assumption of the rate model.
2
Shayunusov, Doston, Dmitry Eskin, Boris V. Balakin, Svyatoslav Chugunov, Stein Tore Johansen, and Iskander Akhatov. "Modeling Water Droplet Freezing and Collision with a Solid Surface." Energies 14, no. 4 (February 16, 2021): 1020. http://dx.doi.org/10.3390/en14041020.
Повний текст джерелаАнотація:
Water droplets released from the sea surface represent one of the major causes of ice accretion on marine vessels. A one-dimensional model of the freezing of a spherical water droplet moving in cold air was developed. The crystallization model allows one to obtain an analytical solution if a uniform temperature distribution over the liquid’s core is assumed. The model was validated using STAR CCM+ Computational fluid dynamics (CFD) code. A collision of a partially frozen droplet with a solid wall assuming the plastic deformation of an ice crust was also considered. The ratio of the crust deformation to the crust thickness was evaluated. It was assumed that if this ratio were to exceed unity, the droplet would stick to the wall’s surface due to ice bridge formation caused by the water released from the droplet’s core.
3
Feddersen, Stefan, Viktoryia Zolatanosha, Ahmed Alshaikh, Dirk Reuter, and Christian Heyn. "Modeling of Masked Droplet Deposition for Site-Controlled Ga Droplets." Nanomaterials 13, no. 3 (January 23, 2023): 466. http://dx.doi.org/10.3390/nano13030466.
Повний текст джерелаАнотація:
Site-controlled Ga droplets on AlGaAs substrates are fabricated using area selective deposition of Ga through apertures in a mask during molecular beam epitaxy (MBE). The Ga droplets can be crystallized into GaAs quantum dots using a crystallization step under As flux. In order to model the complex process, including the masked deposition of the droplets and a reduction of their number during a thermal annealing step, a multiscale kinetic Monte Carlo (mkMC) simulation of self-assembled Ga droplet formation on AlGaAs is expanded for area-selective deposition. The simulation has only two free model parameters: the activation energy for surface diffusion and the activation energy for thermal escape of adatoms from a droplet. Simulated droplet numbers within the opening of the aperture agree quantitatively with the experimental results down to the perfect site-control, with one droplet per aperture. However, the model parameters are different compared to those of the self-assembled droplet growth. We attribute this to the presence of the mask in close proximity to the surface, which modifies the local process temperature and the As background. This approach also explains the dependence of the model parameters on the size of the aperture.
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ROYENKO, V., R. KHALIKOV, S. KHRAMTSOV, and A. KARMES. "MODELING OF FLOODING BY TEMPERATURE-ACTIVATED WATER SPRAYS." Fire and Emergencies: prevention, elimination 3 (2021): 21–29. http://dx.doi.org/10.25257/fe.2021.3.21-29.
Повний текст джерелаАнотація:
Purpose. Fire extinguishing efficiency of flooding with temperature-activated water (TAW) sprays depends on the constituent droplets size and their distribution density. This work is aimed at determining effective characteristics of TAW polydisperse droplet phase for extinguishing fires in confined spaces. The research objectives are: 1) theoretical research of TAW extinguishing capacity dependence on its discharge parameters; 2) developing a generalized model of droplet motion in highly heated fluxes based on the physical process of TAW droplets evaporation in hightemperature environment; 3) modeling the evaporation process of TAW polydisperse droplet phase using the MathLab hardwaresoftware system. Methods. Chemical thermodynamics theory has been used to study evaporation and motion processes of TAW droplet phase. Similarity theory and algorithms theory have been used to simulate the evaporation process of TAW polydisperse droplet phase. Findings. The research has made it possible to establish that the most effective fire extinguishing characteristics are exhibited by temperature-activated water sprays, having droplets with a diameter of less than 5 µm distribution density of more than 60 %. In addition, it has been found that evaporation process of TAW sprays containing a greater number of first mode droplets has a parabolic-asymptotic character. Research application field. The compiled model can be applied to describe the evaporation process of water polydisperse media in highly heated fluxes, as well as to increase flooding efficiency with TAW sprays. Conclusions. Flooding process by means of TAW simulation makes it possible to determine the most effective fire extinguishing characteristics of its discharge for flooding. In further studies, it is advisable to simulate TAW sprays with inhibiting water-soluble salts evaporation process.
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Kumar, Amitesh, Seshadev Sahoo, Sudipto Ghosh, and Brij Kumar Dhindaw. "Effect of Process Parameters on Splat Formation during Impingement of Liquid Metal Droplets over a Cold Substrate." Materials Science Forum 710 (January 2012): 186–91. http://dx.doi.org/10.4028/www.scientific.net/msf.710.186.
Повний текст джерелаАнотація:
Molten metal droplet impingement is an integral part of droplet based manufacturing processes like spray casting and sprays coating. In these processes, in a single operation, a liquid metal stream is atomized into fine droplets, which impact on a substrate to form a bulk deposit. The properties of casting or coating strongly depend on the shape of splats formed by individual droplets after impingement and solidification. Therefore, considerable research studies have been carried out to characterize individual droplet impact, usually driven by an interest in a particular process. These studies include extensive modeling of droplet deposition, some of which are supported by experimental studies. Most of these modeling activities have focused on the impingement of a droplet on to a surface to predict quantities such as the extent of maximum spread and the final equilibrium diameter, the rate of heat transfer to the substrate, and the solidification rate. Due to interaction of several complex phenomena, comprehensive modeling of the droplet deposition is a challenging task. The flow of liquid droplet upon impingement is itself a complex phenomenon. Heat transfer and solidification occurring concurrently with the flow adds further to the complexity. Thus the present study aims at the development of a comprehensive mathematical model of impingement of liquid metal droplet upon a substrate to understand the effect of process parameters such as initial temperature of droplet, size of droplet and velocity of droplet.
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Pokharel, Sagar, Albina Tropina, and Mikhail Shneider. "Numerical Modeling of Laser Heating and Evaporation of a Single Droplet." Energies 16, no. 1 (December 29, 2022): 388. http://dx.doi.org/10.3390/en16010388.
Повний текст джерелаАнотація:
Laser technology is being widely studied for controlled energy deposition for a range of applications, including flow control, ignition, combustion, and diagnostics. The absorption and scattering of laser radiation by liquid droplets in aerosols affects propagation of the laser beam in the atmosphere, while the ignition and combustion characteristics in combustion chambers are influenced by the evaporation rate of the sprayed fuel. In this work, we present a mathematical model built on OpenFOAM for laser heating and evaporation of a single droplet in the diffusion-dominated regime taking into account absorption of the laser radiation, evaporation process, and vapor flow dynamics. The developed solver is validated against available experimental and numerical data for heating and evaporation of ethanol and water droplets. The two main regimes—continuous and pulsed laser heating—are explored. For continuous laser heating, the peak temperature is higher for larger droplets. For pulsed laser heating, when the peak irradiance is close to transition to the boiling regime, the temporal dynamics of the droplet temperature does not depend on the droplet size. With the empirical normalization of time, the dynamics of the droplet shrinkage and cooling are found to be independent of droplet sizes and peak laser intensities.
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Akdag, Osman, Yigit Akkus, Barbaros Çetin, and Zafer Dursunkaya. "Modeling the Evaporation of Drying Sessile Droplets with Buoyancy Driven Internal Convection." E3S Web of Conferences 321 (2021): 04013. http://dx.doi.org/10.1051/e3sconf/202132104013.
Повний текст джерелаАнотація:
Droplet evaporation is a fundamental phenomenon encountered in diverse applications such as inkjet printing, DNA mapping, film coating, and electronics cooling. Modeling the evaporation process of a sessile droplet is complicated because of the coupling of several physical phenomena occurring in different phases and various magnitudes such as the buoyant convection of the liquid in millimeter size droplets and that of the surrounding air/water vapor mixture, in the order of meters. In this study, the theoretical framework presented previously for the steadily fed droplets [Int J Therm Sci, 158 (2020) 106529] is extended to resolve the evaporation of drying droplets with a pinned contact line. Based on the quasi-steady-state assumption, buoyant convection inside the droplet and diffusive-convective transport of vapor in the gas domain are modeled. As a test case, drying process of a water droplet with a 68° initial contact angle on a heated substrate is simulated and the predictions of the model are interpreted.
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LUO, K. H., J. XIA, and E. MONACO. "MULTISCALE MODELING OF MULTIPHASE FLOW WITH COMPLEX INTERACTIONS." Journal of Multiscale Modelling 01, no. 01 (January 2009): 125–56. http://dx.doi.org/10.1142/s1756973709000074.
Повний текст джерелаАнотація:
This paper presents a variety of modeling and simulation methods for complex multiphase flow at microscopic, mesoscopic and macroscopic scales. Each method is discussed in terms of its scale-resolving capability and its relationship with other approaches. Examples of application are provided using a liquid–gas system, in which complex multiscale interactions exist among flow, turbulence, combustion and droplet dynamics. Large eddy simulation (LES) is employed to study the effects of a very large number of droplets on turbulent combustion in two configurations in a fixed laboratory frame. Direct numerical simulation (DNS) in a moving frame is then deployed to reveal detailed dynamic interactions between droplets and reaction zones. In both the LES and the DNS, evaporating droplets are modeled in a Lagrangian macroscopic approach, and have two-way couplings with the carrier gas phase. Finally, droplet collisions are studied using a multiple-relaxation-time lattice Boltzmann method (LBM). The LBM treats multiphase flow with real-fluid equations of state, which are stable and can cope with high density ratios. Examples of successful simulations of droplet coalescence and off-center separation are given. The paper ends with a summary of results and a discussion on hybrid multiscale approaches.
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Sinha, Anubhav, and RV Ravikrishna. "LES of spray in crossflow – Effect of droplet distortion." International Journal of Spray and Combustion Dynamics 9, no. 1 (June 22, 2016): 55–70. http://dx.doi.org/10.1177/1756827716652511.
Повний текст джерелаАнотація:
The present investigation is focused on modeling of spray in crossflow using Large Eddy Simulations (LES). The modeling efforts are supported by experiments which are used both to provide accurate boundary and initial conditions and to evaluate droplet shapes in the near nozzle region. The droplets are modeled as Lagrangian parcels in an Eulerian continuum. Droplets in such configuration have been found to be distorted and not in perfect spherical shape from experimental results of our previous study. Droplet distortion is computed by Taylor-Analogy Breakup (TAB) distortion model. Each droplet is modelled as damped spring-mass system, where surface tension acts as a spring on the mass of the droplet and viscous dissipation provides the damping effect. The effort is to examine the effect of drag law used and the effect of this distortion on the droplet sizes produced in the flow field. Spray wind-ward trajectory and droplet sizes obtained from simulations are compared with the experimental results available. Although computational spray trajectory shows a reasonable match with experimental values, droplet sizes using the standard TAB model are found to be larger than that from experimental observation. To account for this distortion and its role in early breakup of droplets, constants of the TAB model are modified and the droplet sizes are found to be in good agreement with the experimental data.
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Wu, Jiandong, Jiyun Xu, and Hao Wang. "Numerical simulation of micron and submicron droplets in jet impinging." Advances in Mechanical Engineering 10, no. 10 (October 2018): 168781401880531. http://dx.doi.org/10.1177/1687814018805319.
Повний текст джерелаАнотація:
Micron droplet deposition onto a wall in an impinging jet is important for various applications like spray cooling, coating, fuel injection, and erosion. The impinging process is featured by abrupt velocity changes and thus complicated behaviors of the droplets. Either modeling or experiment for the droplet behaviors is still challenging. This study conducted numerical modeling and compared with an existing experiment in which concentric dual-ring deposition patterns of micron droplets were observed on the impinging plate. The modeling fully took into account of the droplet motion in the turbulent flow, the collision between the droplets and the plate, as well as the collision, that is, agglomeration among droplets. Different turbulence models, that is, the v2− f model, standard k–ε model, and Reynolds stress model, were compared. The results show that the k–ε model failed to capture the turbulent flow structures and overpredicted the turbulent fluctuations near the wall. Reynolds stress model had a good performance in flow field simulation but still failed to reproduce the dual-ring deposition pattern. Only the v2− f model reproduced the dual-ring pattern when coupled with droplet collision models. The results echoed the excellent performance of the v2− f model in the heat transfer calculation for the impinging problems. The agglomeration among droplets has insignificant influence on the deposition.
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Acquaviva, P., Chen-An Chen, Jung-Hoon Chun, and Teiichi Ando. "Thermal Modeling of Deposit Solidification in Uniform Droplet Spray Forming." Journal of Manufacturing Science and Engineering 119, no. 3 (August 1, 1997): 332–40. http://dx.doi.org/10.1115/1.2831111.
Повний текст джерелаАнотація:
In spray forming, the deposit thermal state is a key parameter which influences the microstructural evolution upon and after droplet impact onto the deposit. The uniform droplet spray (UDS) forming process has been developed to enable precise control of the droplet and deposit thermal state and the resultant material microstructure. By having a uniform droplet size throughout the spray, all the droplets deposited onto the substrate will have the same thermal state upon impact, allowing for precise control of the solidification process. This paper describes a one-dimensional, finite difference model that predicts the temperature and liquid fraction of the deposit during the UDS process. The model employs an explicit temperature-enthalpy method to incorporate a variety of solidification models. Experiments were conducted using Sn-15 wt percent Pb binary alloy. Temperatures were measured in the deposit and acceptable agreement with the simulation was obtained. Modeling has shown that the deposit thermal state is highly dependent on variations in spray conditions, which are predicted using droplet trajectory and droplet thermal models. Using the droplet and deposit models, the relationship between UDS process parameters and material microstructure can be understood.
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Subramani, Nithya, Sangeetha M., Vijayaraja Kengaiah, and Sai Prakash. "Numerical modeling on dynamics of droplet in aircraft wing structure at different velocities." Aircraft Engineering and Aerospace Technology 94, no. 4 (October 13, 2021): 553–58. http://dx.doi.org/10.1108/aeat-04-2021-0115.
Повний текст джерелаАнотація:
Purpose The purpose of this paper is to find the droplets impact on the airplane wing structure. Two kinds of characteristics of the droplet at different velocity and viscosity are assumed. The droplet is assumed to be spherical cubic form and it is injected from the convergent divergent nozzle with a passive control. Design/methodology/approach This paper presents the results of a numerical simulation of droplet impact on the horizontal surface. The effects of impact parameters are studied. The splash effect of the droplet also visualized. The results are presented in form of stress, strain, displacement magnitude of the droplet. Findings Crosswire is used as passive control. The behavior of the droplet impact is observed based on the kinetic energy and the gravitational forces. Originality/value The results predict that smooth particle hydrodynamic designed droplet not only depend on the equation of state of the droplet but also the injection velocity from the nozzle. It also determined that droplet velocity is depending on the viscosity of the fluid.
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Ibrahim, Ali M., Jose I. Padovani, Roger T. Howe, and Yasser H. Anis. "Modeling of Droplet Generation in a Microfluidic Flow-Focusing Junction for Droplet Size Control." Micromachines 12, no. 6 (May 21, 2021): 590. http://dx.doi.org/10.3390/mi12060590.
Повний текст джерелаАнотація:
In this paper, we study the parameters that affect the generation of droplets in a microfluidic flow-focusing junction. Droplets are evaluated based on the size and frequency of generation. Droplet size control is essential for microfluidic lab-on-a-chip applications in biology, chemistry, and medicine. We developed a three-dimensional numerical model that can emulate the performance of the physical system. A numerical model can help design droplet-generation chips with new junction geometries, different dispersed and continuous phase types, and different flow rates. Our model uses a conservative level-set method (LSM) to track the interface between two immiscible fluids using a fixed mesh. Water was used for the dispersed phase and mineral oil for the continuous phase. The effects of the continuous-to-dispersed flow rate ratio (Qo/Qw) and the surfactant concentration on the droplet generation were studied both using the numerical model and experimentally. The numerical model was found to render results that are in good agreement with the experimental ones, which validates the LSM model. The validated numerical model was used to study the time effect of changing Qo/Qw on the generated droplet size. Properly timing when the flow rates are changed enables control over the size of the next generated droplet, which is useful for single-droplet size modulation applications.
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Yu, Fei, and Benjamin D. Shaw. "Interpretation of Backlit Droplet Images from ISS Droplet Combustion Experiments." Gravitational and Space Research 2, no. 1 (July 1, 2014): 82–93. http://dx.doi.org/10.2478/gsr-2014-0007.
Повний текст джерелаАнотація:
ABSTRACT Backlit droplet images are evaluated for droplet combustion experiments that have been performed on the International Space Station. The focus of the present analyses is on non-sooting or lightly-sooting droplets. The influences of diffraction, interference, and partial coherence on droplet images are considered via Fourier optics modeling. It is found that light diffraction at the droplet edge can contribute significantly to errors in droplet size measurements. Other error sources include background light variations and partial coherence effects. An image-processing algorithm is proposed to account for the effects of diffraction, partial coherence, and background light variations on measurements of droplet sizes.
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Shebeleva, Anna, Andrey Minakov, Alexander Lobasov, and Alexander Shebelev. "Numerical modelling of destruction of a drop of non-Newtonian fluid in a gas flow." EPJ Web of Conferences 196 (2019): 00042. http://dx.doi.org/10.1051/epjconf/201919600042.
Повний текст джерелаАнотація:
The research presents the numerical modeling findings of the secondary breakup of droplets of coal water slurries containing petrochemicals (CWSP) droplet with the filter cake content of 50 % for different Weber number values. The modeling method of the secondary droplet breakup is based on the VOF method for interface resolution, LES model for describing turbulence, and the technology of adapted dynamic grids. This technology enables the grid to be automatically concentrated in the region of large solution gradients during the calculation. The implementation of such a highly detailed grid allowed resolving secondary droplets with the dimensions down to 15 μm. We established the droplet breakup modes depending on the Weber number ranging from 36 to 342. The structure of the stream behind droplets was studied in detail and the numerical method was tested. The results are in good agreement with the results of known experiments.
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Helmers, Thorben, Philip Kemper, Jorg Thöming, and Ulrich Mießner. "Modeling the Excess Velocity of Low-Viscous Taylor Droplets in Square Microchannels." Fluids 4, no. 3 (September 2, 2019): 162. http://dx.doi.org/10.3390/fluids4030162.
Повний текст джерелаАнотація:
Microscopic multiphase flows have gained broad interest due to their capability to transfer processes into new operational windows and achieving significant process intensification. However, the hydrodynamic behavior of Taylor droplets is not yet entirely understood. In this work, we introduce a model to determine the excess velocity of Taylor droplets in square microchannels. This velocity difference between the droplet and the total superficial velocity of the flow has a direct influence on the droplet residence time and is linked to the pressure drop. Since the droplet does not occupy the entire channel cross-section, it enables the continuous phase to bypass the droplet through the corners. A consideration of the continuity equation generally relates the excess velocity to the mean flow velocity. We base the quantification of the bypass flow on a correlation for the droplet cap deformation from its static shape. The cap deformation reveals the forces of the flowing liquids exerted onto the interface and allows estimating the local driving pressure gradient for the bypass flow. The characterizing parameters are identified as the bypass length, the wall film thickness, the viscosity ratio between both phases and the C a number. The proposed model is adapted with a stochastic, metaheuristic optimization approach based on genetic algorithms. In addition, our model was successfully verified with high-speed camera measurements and published empirical data.
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Cao, Zhen Ning, and Pingsha Dong. "Modeling of GMA Weld Pools With Consideration of Droplet Impact." Journal of Engineering Materials and Technology 120, no. 4 (October 1, 1998): 313–20. http://dx.doi.org/10.1115/1.2807020.
Повний текст джерелаАнотація:
A three-dimensional weld pool model has been developed to study the fluid flow and heat transfer process during gas metal arc (GMA) welding. Both droplet heat content and impact force were considered in analyzing the effect of droplets on the formation of weld pool. The fluid flow in the weld pool was induced by the presence of surface tension, electromagnetic and buoyancy force. The surface deformation of weld pool was calculated by considering arc pressure and droplet impact force. Computational results under partial and full penetration welding conditions were obtained. The effect of heat flow and fluid flow characteristics on weld pool geometry was discussed, particularly with respect to the presence of droplet heat input and impact force.
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Al Zaitone, Belal, Abdulrahim Al-Zahrani, Osama Ahmed, Usman Saeed, and Aqeel Ahmad Taimoor. "Spray Drying of PEG6000 Suspension: Reaction Engineering Approach (REA) Modeling of Single Droplet Drying Kinetics." Processes 10, no. 7 (July 13, 2022): 1365. http://dx.doi.org/10.3390/pr10071365.
Повний текст джерелаАнотація:
The spray drying technique is suitable for different kinds of liquid dispersions and can be easily optimized to produce solid particles with tailored properties. The spray drying technique is a complex process. As an example, it is difficult to track drying kinetics, shape, and morphological changes on the scale of a single droplet. To better understand the effect of drying process variables on dried particle formation, it is useful to observe the drying of single droplets. Fundamental processes, such as mass and heat transfer, can then be easily monitored and compared with theoretical models. Acoustic levitation enables droplet/particle suspension in the air without any mechanical contact. Experiments in the acoustic levitator can be used to mimic the drying process in the spray dryer. The drying kinetics of single droplets of PEG6000 into solid particles was studied. Droplets with an initial polymer concentration (PEG6000 aqueous solution of 5%, 10%, and 15% (w/w)) were investigated at different gas drying temperatures. The size of the droplet, moisture content, and the shape evolution of the droplet/particle during the drying process were studied. The experimental drying curves were compared with the Reaction Engineering Approach (REA). The REA models were shown to provide a very good agreement for drying behavior, with a relative error of about ±3% between the initial and predicted droplet mass. This model can be implemented into the large-scale modeling of spray drying using Computational Fluid Dynamics (CFD).
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KUSANO, Shigeyuki, Tomohisa DAN, Jiro SENDA, and Hajime FUJIMOTO. "Modeling on Droplet Evaporation." Transactions of the Japan Society of Mechanical Engineers Series B 65, no. 630 (1999): 804–11. http://dx.doi.org/10.1299/kikaib.65.804.
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Delvigne, Gerard A. L. "On Scale Modeling of Oil Droplet Formation from Spilled Oil." International Oil Spill Conference Proceedings 1991, no. 1 (March 1, 1991): 501–6. http://dx.doi.org/10.7901/2169-3358-1991-1-501.
Повний текст джерелаАнотація:
ABSTRACT Oil droplets form through various processes when oil is spilled at sea:Breakup of the oil surface layer by breaking waves and intrusion of the droplets into the water column (natural dispersion)Enhanced breakup of the oil layer by application of dispersants (chemical dispersion)Breakup of oil lumps from a subsurface spill by turbulence in the waterEntrainment of droplets from a boomed oil slick caused by a large difference in velocity between the oil and the waterBreakup of oil droplets after disposal of oily water into the turbulent wake of a ship. The formation of droplets from a coherent oil mass has been found to be dependent on a complex structure of process parameters, for example, the turbulent eddy structure in the water, internal breaking waves on the oil-water interface, and viscosity and interfacial tension of the oil. The behavior of oil and oil droplet formation in the above processes can be studied relatively easily in small-scale laboratory models, provided that the scaling rules are understood and the laboratory results can be interpreted in terms of field situations. Several laboratory model studies of oil droplet formation were performed by Delft Hydraulics. Much attention was paid to scaling rules and the reliable interpretation of the results in terms of field conditions. Results and conclusions about the modeling process are discussed.
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Lei, Lei, Hong Bo Zhang, Donald J. Bergstrom, Bing Zhang, and Wen Jun Zhang. "Modeling of Droplet Generation by a Modified T-Junction Device Using COMSOL." Applied Mechanics and Materials 705 (December 2014): 112–16. http://dx.doi.org/10.4028/www.scientific.net/amm.705.112.
Повний текст джерелаАнотація:
This paper presents a numerical study of the formation of droplets in a novel two-dimensional T-junction device by using a commercial CFD package: COMSOL Multiphysics. Numerical simulations were carried out for different flow conditions. Different flow rates lead to four regimes: continuous flow, droplet generation, detached, and stalled. The capillary number of the cross-flow turns out to be the key factors in the droplet generation process. The simulation results are validated by comparison to the existing experimental data.
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Bodea, Marius, Radu Mureşan, and Virgiliu Călin Prică. "Modeling of Droplet Dynamic and Thermal Behavior during Gas Atomization Process." Materials Science Forum 672 (January 2011): 80–83. http://dx.doi.org/10.4028/www.scientific.net/msf.672.80.
Повний текст джерелаАнотація:
The paper is focused on the physical phenomena that occurs during gas atomization process, like fragmentation mechanism of the molten stream, the secondary breakup mechanism, droplets velocities and particles temperature history. The modeling of droplet dynamic and thermal history was achieved by using a software program realized by authors, called MetLAB, using the heat balance equations between the cooling gas and the molten metal droplets.
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Zhou, Ronghong, Sheng Li, Liang Shi, Ningning Wang, Yong Liu, and Haihu Liu. "Modeling and simulation of the penetration of a compound droplet into a throat in a pore-throat structure." Physics of Fluids 35, no. 2 (February 2023): 023328. http://dx.doi.org/10.1063/5.0134587.
Повний текст джерелаАнотація:
We present a theoretical and numerical study of a compound droplet flowing through a single pore-throat structure. By quantifying the capillary pressures in the pore and throat under various geometrical conditions, we derive a theoretical model to predict whether the compound droplet is able to penetrate into the throat in a pore-throat structure. Meanwhile, the lattice Boltzmann simulations are conducted to assess the capability and accuracy of the theoretical model. Through a combination of theoretical analysis and lattice Boltzmann simulations, we then investigate the effect of inner droplet size, compound droplet size, and surface wettability on the invasion behavior of a compound droplet. The results show that with increasing the inner droplet size or the compound droplet size, the compound droplet undergoes the transition from the state where the entire compound droplet can pass through the throat to the state where only a part of outer droplet penetrates into and blocks the throat. Although the theoretical predictions show good agreement with the simulation results for most of the cases investigated, it is found that the proposed theoretical model is not applicable to the cases in which the droplets are intermediate-wetting or wetting to the solid surface. This is because the shape of newly formed interface in the pore significantly deviates from the initial circle, which violates the assumption made in the derivation of the theoretical model.
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Meireles, Rúben, Leandro Magalhães, André Silva, and Jorge Barata. "Description of a Eulerian–Lagrangian Approach for the Modeling of Cooling Water Droplets." Aerospace 8, no. 9 (September 18, 2021): 270. http://dx.doi.org/10.3390/aerospace8090270.
Повний текст джерелаАнотація:
The present paper describes a tool developed in-house for the modeling of free-falling water droplet cooling processes. A two-way coupling model is employed to account for the interactions between the droplets and the carrier fluid, following a Eulerian–Lagrangian approach. In addition, a stochastic separated flow technique is employed, involving random sampling of the fluctuating fluid velocity. In physical modeling, two empirical correlations are considered for determining the heat and mass transfer coefficients, with the possibility of accounting for vibrations. The numerical results indicate the preponderance of the interactions between droplet and carrier fluid at various humidity ratios.
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Jungwirth, Pavel, and Victoria Buch. "Van der Waals Attraction and Coalescence of Aqueous Salt Nanodroplets." Collection of Czechoslovak Chemical Communications 68, no. 12 (2003): 2283–91. http://dx.doi.org/10.1135/cccc20032283.
Повний текст джерелаАнотація:
Collisions of aqueous salt nanodroplets at zero initial relative velocity are investigated by means of molecular dynamics simulations. The character of the van der Waals interactions, which bring the droplets together and cause coalescence, is described in detail, and the parameters of the droplet-droplet potential are extracted from the collisional trajectories. Concentration and size effects, together with implications for cloud and precipitation modeling are discussed.
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Pekunov, Vladimir Viktorovich. "Simulation of the absorption of gaseous SO2 by fog droplets using a refined interpolation-sectional droplet model." Кибернетика и программирование, no. 2 (February 2020): 19–32. http://dx.doi.org/10.25136/2644-5522.2020.2.33914.
Повний текст джерелаАнотація:
This article examines the problem of numerical simulation of interaction between the gaseous sulfur dioxide emitted by road transport and fog in the conditions of high humidity. For this purpose, the author applies a multi-factor two-phase mathematical model, which takes into account the dynamics of turbulent main phase, dynamics and kinetics of the multi-sectional droplet phase, presence of thermal inconsistencies formed as a result of direct and diffused solar radiation in various ranges, diffusion of sulfur dioxide, and its absorption by the fog droplets. The article carries out a numerical calculation of the corresponding task within the modeling system of environmental processes AirEcology-P, which allows generating the optimal calculation code for a particular mathematical model. The proposed complex mathematical model that descries interaction between the emitted sulfur dioxide gas and the fog droplets is new; it specifies the calculation of the kinetics of droplet phase based on consideration of the additional factor of droplet fusion characteristic to fog. The submodel of the droplet phase was tested in the numerical simulation (the results were compared with the data of direct Lagrangian modeling of the composite of 1,000 droplets), indicating decent accuracy results. The article obtains the results of numerical simulation of interaction between the emitted SO2 and the droplets. The author demonstrates the self-cleaning ability of the atmosphere, the degree of which correlates with the initial concentration of the smallest droplets and the height from the surface.
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Jylhä, Jani-Petteri, Nadir Ali Khan, and Ari Jokilaakso. "Computational Approaches for Studying Slag–Matte Interactions in the Flash Smelting Furnace (FSF) Settler." Processes 8, no. 4 (April 22, 2020): 485. http://dx.doi.org/10.3390/pr8040485.
Повний текст джерелаАнотація:
Computational methods have become reliable tools in many disciplines for research and industrial design. There are, however, an ever-increasing number of details waiting to be included in the models and software, including, e.g., chemical reactions and many physical phenomena, such as particle and droplet behavior and their interactions. The dominant method for copper production, flash smelting, has been extensively investigated, but the settler part of the furnace containing molten high temperature melts termed slag and matte, still lacks a computational modeling tool. In this paper, two commercial modeling software programs have been used for simulating slag–matte interactions in the settler, the target being first to develop a robust computational fluid dynamics (CFD) model and, second, to apply a new approach for molten droplet behavior in a continuum. The latter is based on CFD coupled with the discrete element method (DEM), which was originally developed for modeling solid particle–particle interactions and movement, and is applied here for individual droplets for the first time. The results suggest distinct settling flow phenomena and the significance of droplet coalescence for settling velocity and efficiency. The computing capacity requirement for both approaches is the main limiting factor preventing full-scale geometry modeling with detailed droplet interactions.
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Morrison, H., and J. O. Pinto. "Mesoscale Modeling of Springtime Arctic Mixed-Phase Stratiform Clouds Using a New Two-Moment Bulk Microphysics Scheme." Journal of the Atmospheric Sciences 62, no. 10 (October 1, 2005): 3683–704. http://dx.doi.org/10.1175/jas3564.1.
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Abstract A new two-moment bulk microphysics scheme is implemented into the polar version of the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) to simulate arctic mixed-phase boundary layer stratiform clouds observed during Surface Heat Budget of the Arctic (SHEBA) First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) Arctic Cloud Experiment (ACE). The microphysics scheme predicts the number concentrations and mixing ratios of four hydrometeor species (cloud droplets, small ice, rain, snow) and includes detailed treatments of droplet activation and ice nucleation from a prescribed distribution of aerosol obtained from observations. The model is able to reproduce many features of the observed mixed-phase cloud, including a near-adiabatic liquid water content profile located near the top of a well-mixed boundary layer, droplet number concentrations of about 200–250 cm−3 that were distributed fairly uniformly through the depth of the cloud, and continuous light snow falling from the cloud base to the surface. The impacts of droplet and ice nucleation, radiative transfer, turbulence, large-scale dynamics, and vertical resolution on the simulated mixed-phase stratiform cloud are examined. The cloud layer is largely self-maintained through strong cloud-top radiative cooling that exceeds 40 K day−1. It persists through extended periods of downward large-scale motion that tend to thin the layer and reduce water contents. Droplet activation rates are highest near cloud base, associated with subgrid vertical motion that is diagnosed from the predicted turbulence kinetic energy. A sensitivity test neglecting subgrid vertical velocity produces only weak activation and small droplet number concentrations (<90 cm−3). These results highlight the importance of parameterizing the impact of subgrid vertical velocity to generate local supersaturation for aerosol-droplet closure. The primary ice nucleation mode in the simulated mixed-phase cloud is contact freezing of droplets. Sensitivity tests indicate that the assumed number and size of contact nuclei can have a large impact on the evolution and characteristics of mixed-phase cloud, especially the partitioning of condensate between droplets and ice.
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Druzhinin, Oleg A., and Wu-Ting Tsai. "Investigation of Vortex Structure Modulation by Spume Droplets in the Marine Atmospheric Boundary Layer by Numerical Simulation." Journal of Marine Science and Engineering 10, no. 7 (June 23, 2022): 856. http://dx.doi.org/10.3390/jmse10070856.
Повний текст джерелаАнотація:
Direct numerical simulation (DNS) of a droplet-laden, turbulent Couette airflow over a waved water surface is performed modeling the marine atmospheric boundary (MABL) layer carrying idealized spume droplets. Both the instantaneous and mean flow properties, the characteristics of the vortex structures and the momentum exchange between air turbulence and waved water surface and droplet-mediated momentum transfer are investigated. A Eulerian–Lagrangian approach is employed in DNS where full, 3D Navier–Stokes equations for the carrier air are solved in a Eulerian frame, and the trajectories of individual droplets are simultaneously tracked in a Lagrangian frame. The impact of the droplets on the carrier air flow is modeled via a point force approximation. The droplets size is considered in the range of spume droplet sizes observed in MABL. Various water surface roughness and droplet injection scenarios are considered, and both instantaneous and phase-averaged flow fields, the Reynolds stresses and the eigenvalues of the local air velocity gradient tensor are evaluated in DNS. Numerical results show a strong dependence of the droplet-mediated airflow modification on-the-droplet injection mechanism. Droplets injected with the surrounding air velocity effectively mitigate the vortex structures by reducing their swirling strength and suppress the momentum flux from air turbulence to water surface by weakening both ejections and sweeping events, and thus accelerating the mean flow as compared to the droplet-free flow. On the other hand, droplets injected with the velocities of the Lagrangian particles of the water surface enhance both the swirling strength of the vortex structures and air-flow turbulent stresses and decelerate the mean wind. The results also show that these effects of droplet-mediated flow modification become less pronounced as the water surface wave steepness increases.
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Lin, Zhirong, and Xin Yuan. "Numerical modeling and high-order scheme for wet steam flow." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 230, no. 11 (April 22, 2015): 1846–60. http://dx.doi.org/10.1177/0954406215584394.
Повний текст джерелаАнотація:
A mathematical model of three-dimensional nonequilibrium condensing wet-steam flow is established in Eulerian form, based on conservation laws for a mixture of steam and water droplets. The method of moments is introduced in modeling the droplet spectrum. To describe the nonequilibrium condensing process, models for classical nucleation and enhanced droplet growth are applied. A special high-order implicit scheme is constructed for this condensing flow model. Tables based on IAPWS-IF97 formulae are used in solving the thermal properties of wet steam. The numerical results for a two-dimensional supersonic nozzle and a low-pressure steam turbine stage are compared with experimental data. The good agreement indicates the effectiveness of the condensation model and numerical scheme.
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Grabowski, Wojciech W., Piotr Dziekan, and Hanna Pawlowska. "Lagrangian condensation microphysics with Twomey CCN activation." Geoscientific Model Development 11, no. 1 (January 12, 2018): 103–20. http://dx.doi.org/10.5194/gmd-11-103-2018.
Повний текст джерелаАнотація:
Abstract. We report the development of a novel Lagrangian microphysics methodology for simulations of warm ice-free clouds. The approach applies the traditional Eulerian method for the momentum and continuous thermodynamic fields such as the temperature and water vapor mixing ratio, and uses Lagrangian super-droplets to represent condensed phase such as cloud droplets and drizzle or rain drops. In other applications of the Lagrangian warm-rain microphysics, the super-droplets outside clouds represent unactivated cloud condensation nuclei (CCN) that become activated upon entering a cloud and can further grow through diffusional and collisional processes. The original methodology allows for the detailed study of not only effects of CCN on cloud microphysics and dynamics, but also CCN processing by a cloud. However, when cloud processing is not of interest, a simpler and computationally more efficient approach can be used with super-droplets forming only when CCN is activated and no super-droplet existing outside a cloud. This is possible by applying the Twomey activation scheme where the local supersaturation dictates the concentration of cloud droplets that need to be present inside a cloudy volume, as typically used in Eulerian bin microphysics schemes. Since a cloud volume is a small fraction of the computational domain volume, the Twomey super-droplets provide significant computational advantage when compared to the original super-droplet methodology. Additional advantage comes from significantly longer time steps that can be used when modeling of CCN deliquescence is avoided. Moreover, other formulation of the droplet activation can be applied in case of low vertical resolution of the host model, for instance, linking the concentration of activated cloud droplets to the local updraft speed. This paper discusses the development and testing of the Twomey super-droplet methodology, focusing on the activation and diffusional growth. Details of the activation implementation, transport of super-droplets in the physical space, and the coupling between super-droplets and the Eulerian temperature and water vapor field are discussed in detail. Some of these are relevant to the original super-droplet methodology as well and to the ice phase modeling using the Lagrangian approach. As a computational example, the scheme is applied to an idealized moist thermal rising in a stratified environment, with the original super-droplet methodology providing a benchmark to which the new scheme is compared.
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Bewley, Jennifer L., and Sonia Lasher-Trapp. "Progress on Predicting the Breadth of Droplet Size Distributions Observed in Small Cumuli." Journal of the Atmospheric Sciences 68, no. 12 (December 1, 2011): 2921–29. http://dx.doi.org/10.1175/jas-d-11-0153.1.
Повний текст джерелаАнотація:
Abstract A modeling framework representing variations in droplet growth by condensation, resulting from different saturation histories experienced as a result of entrainment and mixing, is used to predict the breadth of droplet size distributions observed at different altitudes within trade wind cumuli observed on 10 December 2004 during the Rain in Cumulus over the Ocean (RICO) field campaign. The predicted droplet size distributions are as broad as those observed, contain similar numbers of droplets, and are generally in better agreement with the observations when some degree of inhomogeneous droplet evaporation is considered, allowing activation of newly entrained cloud condensation nuclei. The variability of the droplet growth histories, resulting primarily from entrainment, appears to explain the magnitude of the observed droplet size distribution widths, without representation of other broadening mechanisms. Additional work is needed, however, as the predicted mean droplet diameter is too large relative to the observations and likely results from the model resolution limiting dilution of the simulated cloud.
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Pekunov, Vladimir Viktorovich. "Testing of the droplet phase model during the experiment on modeling the formation of acidulous cloud." Программные системы и вычислительные методы, no. 1 (January 2021): 46–52. http://dx.doi.org/10.7256/2454-0714.2021.1.35104.
Повний текст джерелаАнотація:
The problem of numerical modeling of the formation (as a result of condensation growth and droplet collisions) and development of primary acidulous cloud considers various factors: the presence of temperature gradients, turbulence, direct solar radiation heating the air and walls of buildings, diffuse solar radiation (which describes radiation cooling), transfer of gaseous pollutants and their absorption by droplets. The author earlier formulated the corresponding complex mathematical model that takes into account the aforementioned factors. This article sets the task of testing the droplet component of this model through numerical modeling of the processes in the emerging cloud, with subsequent comparison of the results with theoretical and empirical correlations. The author obtained the new results of numerical modeling of acidulous cloud in the air over a vast urban area with high-density development on the basis of the comprehensive mathematical model that takes into account the above listed factors and relies on the interpolation-sectional submodel of droplet phase. The author models the dynamics and kinetics of such cloud that absorbs gaseous sulphur dioxide; and obtains results on the intensity of absorption of this pollutant in the forming cloud. The comparison of these results with the known data (Hrgian-Mazin droplet distribution and interpolation ratio for the water level of the cloud) demonstrated quite a coincidence of droplet distribution and water level of the cloud. The conclusion is made on sufficient adequacy of application of the ecological model that includes a special submodel of droplet phase.
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Wan, Y. P., H. Zhang, X. Y. Jiang, S. Sampath, and V. Prasad. "Role of Solidification, Substrate Temperature and Reynolds Number on Droplet Spreading in Thermal Spray Deposition: Measurements and Modeling." Journal of Heat Transfer 123, no. 2 (December 7, 2000): 382–89. http://dx.doi.org/10.1115/1.1351893.
Повний текст джерелаАнотація:
Numerical analysis and experimental measurements of the flattening degree of plasma sprayed molybdenum and zirconia droplets deposited on different substrate materials are presented. Investigation is focused on the influence of rate of solidification and wetting angle on droplet spreading. Madejski-Zhang model with one-dimensional treatment of solidification as well as heat transfer in the melt, solidified splat and substrate is employed to perform a numerical analysis. A parametric study is conducted to examine the effects of droplet size, impact velocity, superheating of droplets, substrate temperature, thermal contact resistance, and wetting angle on spreading of the splat and its flattening degree. Numerical results show that the time for solidification can be as small as that for spreading and the rate of solidification can greatly influence the flattening degree. A guideline for when the effect of wetting angle and surface tension on droplet deformation can be neglected is derived. A correlation for the relationship between the flattening degree and Reynolds number with the consideration of solidification is deduced, and a criterion for the effect of droplet solidification on impact dynamics to be negligible is given. The limitations of the assumption of isothermal substrate are also discussed. The numerical predictions agree statistically well with the experimental data.
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Boers, R., H. Klein Baltink, H. J. Hemink, F. C. Bosveld, and M. Moerman. "Ground-Based Observations and Modeling of the Visibility and Radar Reflectivity in a Radiation Fog Layer." Journal of Atmospheric and Oceanic Technology 30, no. 2 (February 1, 2013): 288–300. http://dx.doi.org/10.1175/jtech-d-12-00081.1.
Повний текст джерелаАнотація:
Abstract The development of a radiation fog layer at the Cabauw Experimental Site for Atmospheric Research (51.97°N, 4.93°E) on 23 March 2011 was observed with ground-based in situ and remote sensing observations to investigate the relationship between visibility and radar reflectivity. The fog layer thickness was less than 200 m. Radar reflectivity values did not exceed −25 dBZ even with visibilities less than 100 m. The onset and evaporation of fog produce different radar reflectivity–visibility relationships. The evolution of the fog layer was modeled with a droplet activation model that used the aerosol size distribution observed at the 60-m altitude tower level as input. Radar reflectivity and visibility were calculated from model drop size spectra using Mie scattering theory. Since radiative cooling rates are small in comparison with cooling rates due to adiabatic lift of aerosol-laden air, the modeled supersaturation remains low so that few aerosol particles are activated to cloud droplets. The modeling results suggest that the different radar reflectivity–visibility relationships are the result of differences in the interplay between water vapor and cloud droplets during formation and evaporation of the fog. During droplet activation, only a few large cloud droplets remain after successfully competing for water vapor with the smaller activated droplets. These small droplets eventually evaporate (deactivate) again. In the fog dissolution/evaporation stage, only these large droplet need to be evaporated. Therefore, to convert radar reflectivity to visibility for traffic safety products, knowledge of the state of local fog evolution is necessary.
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Saleeby, Stephen M., and William R. Cotton. "A Large-Droplet Mode and Prognostic Number Concentration of Cloud Droplets in the Colorado State University Regional Atmospheric Modeling System (RAMS). Part II: Sensitivity to a Colorado Winter Snowfall Event." Journal of Applied Meteorology 44, no. 12 (December 1, 2005): 1912–29. http://dx.doi.org/10.1175/jam2312.1.
Повний текст джерелаАнотація:
Abstract This paper is the second in a two-part series describing recent additions to the microphysics module of the Regional Atmospheric Modeling System (RAMS) at Colorado State University. These changes include the addition of a large-cloud-droplet mode (40–80 μm in diameter) into the liquid-droplet spectrum and the parameterization of cloud-droplet nucleation through activation of cloud condensation nuclei (CCN) and giant CCN (GCCN). The large-droplet mode was introduced to represent more precisely the natural dual mode of the cloud-droplet distribution. The parameterized droplet nucleation replaces the former estimation of cloud-droplet formation solely from supersaturation calculations. In Part I of this series, details of the improvements to the microphysics were presented, including the set of equations governing the development of cloud droplets in the Lagrangian parcel model that was employed to parameterize this complex process. Supercell simulations were examined with respect to the model sensitivity to the presence and concentration of large cloud droplets, CCN, and GCCN. Part II examines the sensitivity of the model microphysics to imposed aerosol variations in a wintertime snowfall event that occurred over Colorado on 28–29 February 2004. Model analyses and sensitivity are compared with the real-time forecast version 4.3 of RAMS as well as selected snowpack telemetry (SNOTEL) accumulated precipitation data and surface data from Storm Peak Laboratory in Steamboat Springs, Colorado.
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Minko, Aleksandr, Oleg Guskov, Konstantin Arefyev, and Andrey Saveliev. "Physical and Mathematical Modeling of the Interaction of Water Droplets and High-Speed Gas Flow." Applied Sciences 11, no. 23 (November 24, 2021): 11146. http://dx.doi.org/10.3390/app112311146.
Повний текст джерелаАнотація:
Present work is devoted to physical and mathematical modeling of the secondary disintegration of a liquid jet and gas-dynamic breakup of droplets in high-speed air flows. In this work the analysis of the experiments of water droplet breakup in the supersonic flow with Mach numbers up to M = 3 was carried out. The influence of shock wave presence in the flow on the intensity of droplets gas-dynamic breakup is shown. A developed empirical model is presented. It allows to predict the distribution of droplet diameters and velocities depending on the gas flow conditions, as well as the physical properties of the liquid. The effect of the Weber and Reynolds numbers on the rate of droplets gas-dynamic breakup at various Mach numbers is shown. The obtained data can be useful in the development of mathematical models for the numerical simulation of two-phase flows in the combined Lagrange-Euler formulation.
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Elkaseer, Ahmed, Stella Schneider, Yaqi Deng, and Steffen G. Scholz. "Effect of Process Parameters on the Performance of Drop-On-Demand 3D Inkjet Printing: Geometrical-Based Modeling and Experimental Validation." Polymers 14, no. 13 (June 23, 2022): 2557. http://dx.doi.org/10.3390/polym14132557.
Повний текст джерелаАнотація:
As additive manufacturing has evolved, 3D inkjet printing (IJP) has become a promising alternative manufacturing method able to manufacture functional multi-material parts in a single process. However, issues with part quality in terms of dimensional errors and lack of precision still restrict its industrial and commercial applications. This study aims at improving the dimensional accuracy of 3D IJP parts by developing an optimization-oriented simulation tool of droplet behavior during the drop-on-demand 3D IJP process. The simulation approach takes into consideration the effect of droplet volume, droplet center-to-center distance, coverage percentage of jetted droplets, the contact angle of the ink on the solid substrate and coalescence the performance of overlapping droplets, in addition to the number of printed layers. Following the development of the simulation tool using MATLAB, its feasibility was experimentally validated and the results showed a good agreement with a maximum deviation of 2.25%. In addition, the simulated horizontal features are compared with the results of “Inkraster” software, which also illustrates droplet behavior, however, only in 2D. For vertical features, a dial gauge indicator is used to measure the sample height, and the validation results show that the simulation tool can predicate the height of the sample with an average error of 10.89% for a large droplet diameter and 8.09% for a small diameter. The simulation results were found to be in a good agreement with the dimensions of the printed parts. The developed tool was then used to elucidate the effect of resolution of processed TIFF image and droplet diameter on the dimensional accuracy of 3D IJP parts.
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Ashirbekov, Assetbek, Nursultan Zhumatay, Alibek Kuljabekov, Bagdagul Kabdenova, Ernesto Monaco, Lei Wang, and Luis R. Rojas-Solórzano. "Lattice Boltzmann Modeling of a Sessile and a Body Force-Driven Sliding Droplet over a Grooved Surface." Processes 10, no. 11 (November 11, 2022): 2356. http://dx.doi.org/10.3390/pr10112356.
Повний текст джерелаАнотація:
This work presents the numerical modeling of a droplet’s sessile and dynamic behavior on a grooved surface. A droplet is placed on horizontal and vertical sliding conditions to observe its behavior under wettable and non-wettable conditions. The numerical analysis uses the multicomponent multiphase Shan-Chen Lattice Boltzmann Model (SC-LBM). The Cassie–Baxter and Wenzel states are reproduced for the sessile condition, and the enhancement of the contact angle is appreciated under the action of the grooved-ridged horizontal surface. The sliding droplet is analyzed through the Bond number by varying the ratio between the body force and the surface tension number. For Cassie–Baxter and Wenzel wettability conditions, a critical Bond number was discovered above which the sliding droplet will continue to deform indefinitely. The numerical model proved its suitability to predict the gradual deformation of a droplet over a grooved vertical surface subject to a tangential body force until the droplet eventually reaches a sessile condition or a breakup.
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Wang, Ji-Xiang, Wei Yu, Zhe Wu, Xiangdong Liu, and Yongping Chen. "Physics-based statistical learning perspectives on droplet formation characteristics in microfluidic cross-junctions." Applied Physics Letters 120, no. 20 (May 16, 2022): 204101. http://dx.doi.org/10.1063/5.0086933.
Повний текст джерелаАнотація:
Size-controllable micro-droplets obtained in microfluidic cross-junctions are significant in microfluidics. Modeling and predictions in microfluidic-based droplet formation characteristics to date using various traditional theoretical or empirical correlations are far from satisfactory. Driven by unprecedented data volumes from microfluidic experiments and simulations, statistical learning can offer a powerful technique to extract data that can be interpreted into underlying fluid physics and modeling. This Letter historically combines the current experimental data and experimental/numerical data from previous publications as a microfluidics-based droplet formation characteristics database. Two supervised statistical learning algorithms, deep neural network and factorization-machine-based neural network (Deep-FM), were established to model and predict the formed droplet size in microfluidic cross-junctions. As a newly developed statistical learning code in 2017, the Deep-FM manifests a better prediction performance, where the average relative error was only 4.09% and nearly 98% of the data points had individual relative errors of 10% or less. Such high accuracy can be attributed to the outstanding interactions between high-order and low-order features of the Deep-FM framework. Another innovation in this Letter lies in the training dataset shrinkage and optimization without sacrificing the prediction accuracy. Such a method pioneers statistical learning algorithms in small-sample modeling problems, which is different from big data modeling and analyses. The improved statistical learning proposed in this Letter provides universal high-accuracy modeling for microfluidic-based droplet characteristics prediction, which can be an influential data-processing framework that can boost and probably transform current lines of microfluidic physics research and industrial applications.
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Pronkina, Tatiana Vasilievna. "About the influence of the forces of interaction between the droplets on the dynamics of emulsion." Yugra State University Bulletin 15, no. 1 (December 9, 2019): 59–65. http://dx.doi.org/10.17816/byusu20190159-65.
Повний текст джерелаАнотація:
The dynamics of deposition of compound droplets of the emulsion under the action of gravity is investigated. The interaction of the droplet with its inclusion is taken into account. Axisymmetric and asymmetric problems of deposition of compound droplets are considered. Expressions for the relative and absolute velocities of the compound emulsion droplets are found. Based on numerical modeling, the trajectories of the relative and absolute motion of the droplets are obtained.
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Мыслицкая, Н. А., А. В. Цибульникова, В. А. Слежкин, И. Г. Самусев, Ю. Н. Антипов та В. В. Брюханов. "Генерация суперконтинуума в режиме филаментации в водяной капле с наночастицами серебра при низкой температуре". Журнал технической физики 128, № 12 (2020): 1821. http://dx.doi.org/10.21883/os.2020.12.50316.351-20.
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The supercontinuum generation in water droplets with nanoparticles of citrate silver in the temperature range of 2–22 °C, as well as in the ice droplets frozen to −15.0 °C, has been studied. It was found that the intensity of the supercontinuum emission under the excitation by a train of femtosecond laser pulses exponentially decays along the droplet diameter and it increases linearly with increasing NP concentration. The emission spectrum of supercontinuum in water droplet with NPs and the generation of localized plasmons with fluorescence at the 430 nm wavelength was studied. The movement of a heat wave along the diameter of a small frozen drop with a speed of 190 mm / s accompanying exponentially decaying supercontinuum radiation was recorded. The modeling of heat transfer processes in the frozen droplet during the formation of a heat wave has been carried out.
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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.
Повний текст джерелаАнотація:
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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Zhao, Lin, Feng Gao, Michel C. Boufadel, Thomas King, Brian Robinson, and Kenneth Lee. "Effects of tip streaming on the prediction of droplet size distribution in the presence of dispersants during subsea blowouts." International Oil Spill Conference Proceedings 2017, no. 1 (May 1, 2017): 1212–29. http://dx.doi.org/10.7901/2169-3358-2017.1.1212.
Повний текст джерелаАнотація:
Abstract (2017-193) With the presence of surfactants in the fluid mixture, tip streaming phenomenon often occurs where daughter droplets of micron or sub-micron size are ejected from thin threads of the droplet poles. Recent experimental and modeling studies of tip streaming phenomenon have been focusing on the formation of individual droplets. However, effects of tip streaming on the prediction of droplet formation during subsurface oil blowouts have not been thoroughly investigated. Due to the high intensity flow in the blowout, the amount of micron or sub-micron size droplets resulting from tip streaming could be substantial and cannot be ignored. In this study, a new empirical-numerical scheme is developed in the thoroughly-validated droplet formation model, VDROP-J, to account for the tip streaming phenomenon when dispersants are presence. Calibration of the new scheme and model validations are performed in association with the underwater oil jet experiments. The new model development improves the capability of VDROP-J model in application to the cases when dispersants are used, which would provide valuable information of droplet formation during subsea blowouts for decision makers and research groups.
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Miliauskas, Gintautas, Egidijus Puida, Robertas Poškas, and Povilas Poškas. "The Influence of Droplet Dispersity on Droplet Vaporization in the High-Temperature Wet Gas Flow in the Case of Combined Heating." Sustainability 13, no. 7 (March 31, 2021): 3833. http://dx.doi.org/10.3390/su13073833.
Повний текст джерелаАнотація:
The change in the thermal and energy state of the water droplet is defined numerically. The influence of droplet dispersity on the interaction of the transfer processes was evaluated. In influence of the Stefan flow was considered as well. The internal heat transfer of the droplet was defined by the combined heat transfer through effective conductivity and radiation model. The results of the numerical modeling of heat and mass transfer in water droplets in a wet flue gas flow of 1000 °C highlight the influence of the variation in heat transfer regimes in the droplet on the interaction of the transfer processes in consistently varying phase change regimes. The results of the investigation shows that the inner heat convection diminishes intensively in the transitional phase change regime because of a rapid slowdown of the slipping droplet in the gas. The radiation absorption in the droplet clearly decreases only at the final stage of equilibrium evaporation. The highlighted regularities of the interaction between combined transfer processes in water droplets are also valid for liquid fuel and other semi-transparent liquids sprayed into high-temperature flue gas flow. However, a qualitative evaluation should consider individual influence of dispersity that different liquids have.
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Elhadi Ibrahim, Mohamed, and Mamoun Medraj. "Water Droplet Erosion of Wind Turbine Blades: Mechanics, Testing, Modeling and Future Perspectives." Materials 13, no. 1 (December 31, 2019): 157. http://dx.doi.org/10.3390/ma13010157.
Повний текст джерелаАнотація:
The problem of erosion due to water droplet impact has been a major concern for several industries for a very long time and it keeps reinventing itself wherever a component rotates or moves at high speed in a hydrometer environment. Recently, and as larger wind turbine blades are used, erosion of the leading edge due to rain droplets impact has become a serious issue. Leading-edge erosion causes a significant loss in aerodynamics efficiency of turbine blades leading to a considerable reduction in annual energy production. This paper reviews the topic of water droplet impact erosion as it emerges in wind turbine blades. A brief background on water droplet erosion and its industrial applications is first presented. Leading-edge erosion of wind turbine is briefly described in terms of materials involved and erosion conditions encountered in the blade. Emphases are then placed on the status quo of understanding the mechanics of water droplet erosion, experimental testing, and erosion prediction models. The main conclusions of this review are as follow. So far, experimental testing efforts have led to establishing a useful but incomplete understanding of the water droplet erosion phenomenon, the effect of different erosion parameters, and a general ranking of materials based on their ability to resist erosion. Techniques for experimentally measuring an objective erosion resistance (or erosion strength) of materials have, however, not yet been developed. In terms of modelling, speculations about the physical processes underlying water droplet erosion and consequently treating the problem from first principles have never reached a state of maturity. Efforts have, therefore, focused on formulating erosion prediction equations depending on a statistical analysis of large erosion tests data and often with a combination of presumed erosion mechanisms such as fatigue. Such prediction models have not reached the stage of generalization. Experimental testing and erosion prediction efforts need to be improved such that a coherent water droplet erosion theory can be established. The need for standardized testing and data representation practices as well as correlations between test data and real in-service erosion also remains urgent.
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Oruganti, Surya Kaundinya, Guillaume Millet, and Mikhael Gorokhovski. "Assessment of LES-STRIP approach for modeling of droplet dispersion in diesel-like sprays." Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles 74 (2019): 60. http://dx.doi.org/10.2516/ogst/2019025.
Повний текст джерелаАнотація:
In this paper, the stochastic equations of droplet motion in turbulent flow, proposed recently by Gorokhovski and Zamansky (2018, Phys. Rev. Fluids 3, 3, 034602), are assessed for turbulent spray dispersion in diesel like conditions along with Large Eddy Simulation (LES) for the gaseous flow. For droplets above the Kolmogorov length scale, this model introduces the concept of the stochastic drag, independently of laminar viscosity. For droplets below the Kolmogorov length scale, the model equation does depend on the laminar viscosity through the Stokes drag but the particle motion is stochastically forced. Both the stochastic drag and the stochastic forcing of the Stokes drag equation are based on the simple log-normal stochastic process for the viscous dissipation (ϵ) “seen” along the droplet trajectory. In this paper, this model is applied in the framework of two-way coupling, wherein the turbulence generated by the spray inturn controls the spray dispersion. The criterion for the choice of one of the approaches, i.e., the stochastic drag or the stochastic forcing, follows the classical condition for drag coefficient based on the droplet Reynolds number (Re p). The non-vaporizing spray experiments from Engine Combustion Network (ECN) are used as test cases. In addition to the comparison of the spray penetration length, spreading angle and spray structure with the experimental data, a qualitative analysis of the statistics of the droplet acceleration and gas phase velocities is presented. It was shown that the new approach is much more effective in modeling the spray dynamics on relatively coarser mesh. Consequently, the new approach in the framework of two-way coupling may predict the preferential concentration effects better, which is important for spray combustion.
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de Lozar, Alberto, and Lukas Muessle. "Long-resident droplets at the stratocumulus top." Atmospheric Chemistry and Physics 16, no. 10 (May 30, 2016): 6563–76. http://dx.doi.org/10.5194/acp-16-6563-2016.
Повний текст джерелаАнотація:
Abstract. Turbulence models predict low droplet-collision rates in stratocumulus clouds, which should imply a narrow droplet size distribution and little rain. Contrary to this expectation, rain is often observed in stratocumuli. In this paper, we explore the hypothesis that some droplets can grow well above the average because small-scale turbulence allows them to reside at cloud top for a time longer than the convective-eddy time t*. Long-resident droplets can grow larger because condensation due to longwave radiative cooling, and collisions have more time to enhance droplet growth. We investigate the trajectories of 1 billion Lagrangian droplets in direct numerical simulations of a cloudy mixed-layer configuration that is based on observations from the flight 11 from the VERDI campaign. High resolution is employed to represent a well-developed turbulent state at cloud top. Only one-way coupling is considered. We observe that 70 % of the droplets spend less than 0.6t* at cloud top before leaving the cloud, while 15 % of the droplets remain at least 0.9t* at cloud top. In addition, 0.2 % of the droplets spend more than 2.5t* at cloud top and decouple from the large-scale convective eddies that brought them to the top, with the result that they become memoryless. Modeling collisions like a Poisson process leads to the conclusion that most rain droplets originate from those memoryless droplets. Furthermore, most long-resident droplets accumulate at the downdraft regions of the flow, which could be related to the closed-cell stratocumulus pattern. Finally, we see that condensation due to longwave radiative cooling considerably broadens the cloud-top droplet size distribution: 6.5 % of the droplets double their mass due to radiation in their time at cloud top. This simulated droplet size distribution matches the flight measurements, confirming that condensation due to longwave radiation can be an important mechanism for broadening the droplet size distribution in radiatively driven stratocumuli.
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Fedoseev, V. N., and S. A. Loginova. "Mathematical modeling of evaporation processes in a heat pump circuit." Herald of Dagestan State Technical University. Technical Sciences 49, no. 4 (February 10, 2023): 177–81. http://dx.doi.org/10.21822/2073-6185-2022-49-4-177-181.
Повний текст джерелаАнотація:
Objective. In order to improve the control system of an air heat pump and increase its efficiency, it is necessary to take into account as accurately as possible all the elementary stages of the processes occurring in the system under consideration. The article discusses in detail the heat and mass transfer process of evaporation of the refrigerant from the boiling working fluid of a heat pump.Method. Description of heat and mass transfer processes occurring in the evaporator line of an air heat pump.Result. A numerical experiment was carried out to determine the size of the refrigerant droplets that can fly out of the boiling freon liquid during the operation of the heat pump. The calculations performed showed that droplets with a diameter of less than 1 mm have time to evaporate in the vapor flow during the movement from the boiling zone to the droplet eliminator located in front of the compressor.Conclusion. Research will make it possible to develop recommendations for the design of the droplet collection unit, as well as to develop models for optimizing the operating modes of air source heat pumps.
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BARATA, Jorge. "On the modeling of droplet transport, dispersion and evaporation in turbulent flows." Combustion Engines 122, no. 3 (July 1, 2005): 42–55. http://dx.doi.org/10.19206/ce-117399.
Повний текст джерелаАнотація:
The present paper presents a numerical study on evaporating droplets injected through a turbulent cross-stream. Several models have been used with more or less success to describe similar phenomena, but much of the reported work deals only with sprays in stagnant surroundings. The ultimate goal of this study is to develop an Eulerian/Lagragian approach to account for turbulent transport, dispersion, evaporation and coupling between both processes in practical spray injection systems, which usually include air flows in the combustion chamber like swirl, tumble and squish in I.C. engines or crossflow in gas turbines. In this work a method developed to study isothermal turbulent dispersion is extended to the case of an array of evaporating droplets through a crossflow, and the performance of two different evaporation models widely used is investigated. The convection terms were evaluated using the hybrid or the higher order QUICK scheme. The dispersed phase was treated using a Lagrangian reference frame. The differences between the two evaporation models and its applicability to the present flow are analysed in detail. During the preheating period of the Chen and Pereira [1] model the droplets are transported far away from the injector by the crossflow, while with the Sommerfeld [2] formulation for evaporation the droplet has a continuous variation of the diameter. This result has profound implications on the results because the subsequent heat transfer and turbulent dispersion is extremely affected by the size of the particles (or droplets). As a consequence, droplet diameter, temperature and mass fraction distributions were found to be strongly dependent on the evaporation model used. So, a new formulation that takes into account also the transport of the evaporating droplets needs to be developed if practical injection systems are to be simulated. Also, in order to better evaluate and to improve the vaporization models more detailed measurements of three-dimensional configurations are required.