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1
Hurlburt, Evan T., et Ty A. Newell. « Prediction of the Circumferential Film Thickness Distribution in Horizontal Annular Gas-Liquid Flow ». Journal of Fluids Engineering 122, no 2 (16 février 2000) : 396–402. http://dx.doi.org/10.1115/1.483269.
Texte intégralRésumé :
This paper develops a liquid film symmetry correlation and a liquid film thickness distribution model for horizontal annular gas-liquid pipe flows. The symmetry correlation builds on the work of Williams et al. (1996) (Droplet Flux Distributions and Entrainment in Horizontal Gas-Liquid Flows,” Int. J. Multiphase Flow, Vol. 22, pp. 1–18). A new correlating parameter is presented. The liquid film thickness model is based on the work of Laurinat et al. (1985) (Film Thickness Distribution for Gas-Liquid Annular Flow in a Horizontal Pipe,” PhysicoChem. Hydrodynam., Vol. 6, pp. 179–195). The circumferential momentum equation is simplified to a balance between the normal Reynolds stress in the film’s circumferential direction and the circumferential component of the weight of the film. A model for the normal Reynolds stress in the circumferential direction is proposed. The symmetry correlation is used to close the model equations. The model is valid for films with disturbance waves, and is shown to be applicable to air-water flows over a range of conditions from low velocity asymmetric to high velocity symmetric annular flows. [S0098-2202(00)02102-7]
2
Radke, C. J. « Film and membrane-model thermodynamics of free thin liquid films ». Journal of Colloid and Interface Science 449 (juillet 2015) : 462–79. http://dx.doi.org/10.1016/j.jcis.2014.12.079.
Texte intégral
3
Khrustalev, D., et A. Faghri. « Thick-Film Phenomenon in High-Heat-Flux Evaporation From Cylindrical Pores ». Journal of Heat Transfer 119, no 2 (1 mai 1997) : 272–78. http://dx.doi.org/10.1115/1.2824220.
Texte intégralRésumé :
A physical and mathematical model of the evaporating thick liquid film, attached to the liquid-vapor meniscus in a circular micropore, has been developed. The liquid flow has been coupled with the vapor flow along the liquid-vapor interface. The model includes quasi-one-dimensional compressible steady-state momentum conservation for the vapor and also a simplified description of the microfilm at the end of the thick film. The numerical results, obtained for water, demonstrate that formation of extended thick liquid films in micropores can take place due to high-velocity vapor flow under high rates of vaporization. The model has also predicted that the available capillary pressure significantly changes with the wall-vapor superheat and other operational conditions.
4
Rettenmayr, Markus, Oleg Kashin et Stephanie Lippmann. « Simulation of Liquid Film Migration during Melting ». Materials Science Forum 790-791 (mai 2014) : 127–32. http://dx.doi.org/10.4028/www.scientific.net/msf.790-791.127.
Texte intégralRésumé :
Melting of a single-phase polycrystalline material is known to start by the formation of liquid films at the surface and at grain boundaries. The internal liquid films are not necessarily quiescent, but can migrate to avoid/reduce supersaturation in the solid phase. The migration is discussed in the literature to be governed by coherency strains of the solid/liquid interface, by concentration gradients in the liquid or by concentration gradients in the solid phase. A phase transformation model for diffusional phase transformations considering interface thermodynamics (possible deviations from local deviations) has been put up to describe the migration of the solid/liquid (trailing) and the liquid/solid (leading) interfaces of the liquid film. New experimental results on melting in a temperature gradient in combination with simulation calculations reveal that concentration fluctuations in the liquid phase trigger the liquid film migration and determine the migration direction, until after a short time in the order of microseconds the process is governed by diffusion in the solid phase.
5
Isaenkov, Sergey V., Ivan S. Vozhakov, Mikhail V. Cherdantsev, Dmitry G. Arkhipov et Andrey V. Cherdantsev. « Effect of Liquid Viscosity and Flow Orientation on Initial Waves in Annular Gas–Liquid Flow ». Applied Sciences 10, no 12 (25 juin 2020) : 4366. http://dx.doi.org/10.3390/app10124366.
Texte intégralRésumé :
The complex wave structure of annular gas–liquid flow with disturbance waves and liquid entrainment is a result of the evolution of high-frequency initial waves, appearing at the very inlet of the flow, prior to the hydrodynamic stabilization of liquid film. This stage of flow evolution is studied experimentally, using a shadow technique, and theoretically, using a linear stability analysis of the Orr–Sommerfeld equation in both phases. The present work is focused on the comparison of earlier results obtained in air–water downward flow with the new results obtained in upward flow and with more viscous liquids. The flow orientation affects the shape of the liquid film prior to stabilization; the initial film area is thicker but shorter in upward flow. Upward flow orientation also leads to a lower frequency and the increment of growth of initial waves. The viscosity effect is found to be weak if flow rates of both phases are the same. The model is mostly able to reproduce the qualitative trends, but the quantitative agreement is not reached. Experimental observations indicate that the liquid flow within the initial area is significantly different from the stabilized flow of gas-sheared liquid film, which is used in the model. This difference could explain the discrepancy; further development of the model should be aimed at taking into account the evolution of the velocity profile inside the liquid film during the stage of hydrodynamic stabilization.
6
O'Brien, S. B. G., et M. Hayes. « A model for dip-coating of a two liquid mixture ». International Journal of Mathematics and Mathematical Sciences 29, no 6 (2002) : 313–24. http://dx.doi.org/10.1155/s0161171202011614.
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We consider a thin film flow where a flat substrate is coated with a mixture of two miscible liquids, of equal viscosity, and develop a model to predict the evolving coating thicknesses. The developed model can, under certain circumstances, be used as an approximation for the dip-coating of a liquid suspension of a viscous volatile liquid and solid solute as occurs in many industrial applications.
7
Halpern, D., et J. B. Grotberg. « Surfactant Effects on Fluid-Elastic Instabilities of Liquid-Lined Flexible Tubes : A Model of Airway Closure ». Journal of Biomechanical Engineering 115, no 3 (1 août 1993) : 271–77. http://dx.doi.org/10.1115/1.2895486.
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A theoretical analysis is presented predicting the closure of small airways in the region of the terminal and respiratory bronchioles. The airways are modelled as thin elastic tubes, coated on the inside with a thin viscous liquid lining. This model produces closure by a coupled capillary-elastic instability leading to liquid bridge formation, wall collapse or a combination of both. Nonlinear evolution equations for the film thickness, wall position and surfactant concentration are derived using an extended version of lubrication theory for thin liquid films. The positions of the air-liquid and wall-liquid interfaces and the surfactant concentration are perturbed about uniform states and the stability of these perturbations is examined by solving the governing equations numerically. Solutions show that there is a critical film thickness, dependent on fluid, wall and surfactant properties above which liquid bridges form. The critical film thickness, εc, decreases with increasing mean surface-tension or wall compliance. Surfactant increases εc by as much as 60 percent for physiological conditions, consistent with physiological observations. Airway closure occurs more rapidly with increasing film thickness and wall flexibility. The closure time for a surfactant rich interface can be approximately five times greater than an interface free of surfactant.
8
Wittig, S., J. Himmelsbach, B. Noll, H. J. Feld et W. Samenfink. « Motion and Evaporation of Shear-Driven Liquid Films in Turbulent Gases ». Journal of Engineering for Gas Turbines and Power 114, no 2 (1 avril 1992) : 395–400. http://dx.doi.org/10.1115/1.2906604.
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Detailed measurements of wavy liquid films driven by the shear stress of turbulent air flow are obtained for different air temperatures, air velocities, and flow rates of the liquid. The experimental conditions are chosen from characteristic data of liquid film flow in prefilming airblast atomizers and film vaporization employing combustors. For the measurement of the local film thickness and film velocity a new optical instrument—based on the light absorption of the liquid—has been developed, which can be used at high temperatures with evaporation. The measured data of the gas phase and the liquid film are compared with the results of a numerical code using a laminar as well as a turbulent model for the film flow and a standard numerical finite volume code for the gas phase. The results utilizing the two models for the liquid film show that the film exhibits laminar rather than turbulent characteristics under a wide range of flow conditions. This is of considerable interest when heat is transferred across the film by heating or cooling of the wall. With this information the optical instrument can also be used to determine the local shear stress of the gas phase at the phase interface. Using time-averaged values for the thickness, the velocity, and the roughness of the film, the code leads to relatively accurate predictions of the interaction of the liquid film with the gas phase.
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Lapp, Florian Felix, Sebastian Schuster, Simon Hecker et Dieter Brillert. « Experimental Validation of an Analytical Condensation Model for Application in Steam Turbine Design ». International Journal of Turbomachinery, Propulsion and Power 7, no 1 (3 mars 2022) : 9. http://dx.doi.org/10.3390/ijtpp7010009.
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This paper presents experimental data on shear-stress-driven liquid water films on a horizontal plate formed by the condensation of superheated steam. The experimental results were obtained in the Experimental Multi-phase Measurement Application (EMMA) at the University of Duisburg-Essen. The liquid film thickness was spatially and temporally investigated with an optical measurement system. Furthermore, the resulting local heat transfer coefficient in the case of film condensation was determined for a variety of steam velocities and temperatures. Subsequently, the presented data are compared to the results of an analytical condensation model for shear-stress-driven liquid films developed by Cess and Koh. Thus, the model is qualitatively validated, with explicable remaining disparities between the model and experiment that are further discussed. The presented results are an important contribution to the contemporary research into steady-state, single-component multiphase flow considering phase-change phenomena including heat transfer.
10
Borodina, Kseniia A. « MODEL OF THE EVOLUTION OF A BINARY HOMOGENEOUS SOLUTION FILM UNDER THERMAL ACTION ». Tyumen State University Herald. Physical and Mathematical Modeling. Oil, Gas, Energy 6, no 4 (2020) : 48–68. http://dx.doi.org/10.21684/2411-7978-2020-6-4-48-68.
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The research on the motion of liquid films has recently become increasingly important, which is associated with the expanding field of their practical application. For example, the promising methods of cooling include the technologies based on the evaporation of a thin layer of liquid. Based on the Marangoni effects, optical elements of medical diagnostics systems can be developed, the performance of which can be quickly reconfigured for the necessary tasks in comparison with the currently used movable lenses. Many authors in Russia and abroad are engaged in a comprehensive theoretical study of film flows, which should not lag behind the studies of the possibilities of their application. At the same time, the motion of films of a binary homogeneous solution has not been studied enough, and this is the object of this study. This paper considers the behavior of a liquid film containing a volatile component when it is heated. The importance of taking into account the Laplace pressure jump at the interface is indicated, as well as the effect of surface curvature on the saturated vapor pressure. Formulation of the problem is formalized in a limited volume. The stability of the numerical scheme was investigated by the harmonics method. The results confirm the reliability of the model by testing it on a number of problems with analytical solutions: preservation of a liquid volume when a film in a gravity field touches a vertical wall; determination of the profile of the liquid layer with uneven heating of the substrate; mass balance at uniform heating and cooling.
11
Wu, Ou Yang, Jia Qian, Zhang Fan, Xiao Yang Yuan et Qing Feng Meng. « Lubrication Model and Dynamic Characteristics of Distributed Liquid Film for Hydrodynamic Bearing ». Advanced Materials Research 744 (août 2013) : 194–98. http://dx.doi.org/10.4028/www.scientific.net/amr.744.194.
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For the thin film lubrication, boundary lubrication, and local dry friction lubrication state of hydrodynamic bearing, a lubrication model of distributed liquid film is established in this paper which is designed to service for calculating or predicting the full life cycle design performance of water-lubricated bearing. The limitations of the fluid-solid-thermal coupling model for describing the distributed liquid film are investigated. Two new methods to build the lubrication model of distributed liquid film are given. The first one takes fluid-solid-thermal model that can guide the design of bearings parameters as dominant factor, and combines with wear, corrosion, two-phase of gas-liquid and other additional factors. A comprehensive model integrating simulation and mechanism can be built. Through researching the regional properties or distributed parameter of water film and solid interface, the second way proposes a decomposition and synthesis modeling method of water film and rubber. A distributed parameters model of dynamic characteristics for water-lubricated bearing is built. The lubrication theory of distributed liquid film proposed in this paper is appropriate for the situation when the film thickness is less than 10μm or contact. When the film thickness is greater than 10μm, classical lubrication theory is applicable.
12
Penn, David G., Martin Lopez de Bertodano, Paul S. Lykoudis et Stephen G. Beus. « Dry Patch Stability of Shear Driven Liquid Films ». Journal of Fluids Engineering 123, no 4 (26 juin 2001) : 857–62. http://dx.doi.org/10.1115/1.1412459.
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The breakdown of the liquid film at the wall in annular gas-liquid flow may lead to the formation of a stable dry patch. For the case of heat transfer surfaces this causes a hot spot. Dry patch stability depends on a balance of body and surface forces. In the present study the film is driven by the interfacial shear force and the gravity force is negligible. Hartley and Murgatroyd proposed a model for dry patches of shear driven films based on a balance of surface tension and inertia but the film contact angle had to be adjusted to an unrealistic value to fit the model to experimental data. Murgatroyd later proposed an additional force because the wall and the interfacial shear stresses on the film are unbalanced near the dry patch. The magnitude of the net shear force on the film is determined by a characteristic length, λ, over which this imbalance occurs. However, Murgatroyd did not validate the model with a mathematical solution for the distribution of the shear stresses but determined λ empirically to fit the experimental data. A new computational fluid dynamics (CFD) solution of the flow field in the film around the dry patch has been obtained. The CFD results confirm Murgatroyd’s hypothesis, although the details are more complex. In addition new experimental data for adiabatic upward annular air-water and air-ethylene glycol flows provide further validation for Murgatroyd’s model.
13
Wu, Zhenpeng, Vanliem Nguyen, Zhihong Zhang et Liangcai Zeng. « Study on curved surface design of sliding pair based on stepped topography model ». Industrial Lubrication and Tribology 72, no 1 (30 août 2019) : 86–92. http://dx.doi.org/10.1108/ilt-04-2019-0121.
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Purpose The stepped topography of the friction pairs mainly causes the fluid film thickness to change in the direction of motion. In this region, there have very few topographical design methods for continuous or non-linear distribution of the fluid film. The purpose of this study is to analyze the effect of the curved surface on the performance of the liquid film. Design/methodology/approach First, a numerical simulation is used to solve the optimal bearing capacity and friction coefficient of the liquid film under the condition of the minimum film thickness. Then, the curved surface described by the sinusoidal curve equation is applied in the transitional region of maximum and minimum film thickness. The bearing capacity and the friction coefficient of the liquid film are respectively simulated and compared in the same condition of the minimum film thickness. Findings The research results show that the liquid film using the curved surface transition model, the optimal bearing capacity is significantly increased by 32 per cent while the optimal friction coefficient is clearly reduced by 38 per cent in comparison with using stepped surface model. Originality/value The friction pair with curved transition enables better lubrication performance of the liquid film and better adaptability under unstable conditions.
14
Champougny, Lorène, Emmanuelle Rio, Frédéric Restagno et Benoit Scheid. « The break-up of free films pulled out of a pure liquid bath ». Journal of Fluid Mechanics 811 (14 décembre 2016) : 499–524. http://dx.doi.org/10.1017/jfm.2016.758.
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In this paper, we derive a lubrication model to describe the non-stationary free liquid film that is created when a vertical frame is pulled out of a liquid reservoir at a given velocity. We here focus on the case of a pure liquid, corresponding to a stress-free boundary condition at the liquid/air interfaces of the film, and thus employ an essentially extensional description of the flow. Taking into account van der Waals interactions between the interfaces, we observe that film rupture is well defined in time as well as in space, which allows us to compute the critical thickness and the film height at the moment of rupture. The theoretical predictions of the model turn out to be in quantitative agreement with experimental measurements of the break-up height of silicone oil films in a wide range of pulling velocities and supporting fibre diameters.
15
Camassa, Roberto, H. Reed Ogrosky et Jeffrey Olander. « Viscous film flow coating the interior of a vertical tube. Part 1. Gravity-driven flow ». Journal of Fluid Mechanics 745 (25 mars 2014) : 682–715. http://dx.doi.org/10.1017/jfm.2014.90.
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AbstractThe gravity-driven flow of a viscous liquid film coating the inside of a tube is studied both theoretically and experimentally. As the film moves downward, small perturbations to the free surface grow due to surface tension effects and can form liquid plugs. A first-principles strongly nonlinear model based on long-wave asymptotics is developed to provide simplified governing equations for the motion of the film flow. Linear stability analysis on the basic solution of the model predicts the speed and wavelength of the most unstable mode, and whether the film is convectively or absolutely unstable. These results are found to be in remarkable agreement with the experiments. The model is also solved numerically to follow the time evolution of instabilities. For relatively thin films, these instabilities saturate as a series of small-amplitude travelling waves, while thicker films lead to solutions whose amplitude becomes large enough for the liquid surface to approach the centre of the tube in finite time, suggesting liquid plug formation. Next, the model’s periodic travelling wave solutions are determined by a continuation algorithm using the results from the time evolution code as initial seed. It is found that bifurcation branches for these solutions exist, and the critical turning points where branches merge determine film mean thicknesses beyond which no travelling wave solutions exist. These critical thickness values are in good agreement with those for liquid plug formations determined experimentally and numerically by the time-evolution code.
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Seiwert, Jacopo, Juliette Pierre et Benjamin Dollet. « Coupled vibrations of a meniscus and liquid films ». Journal of Fluid Mechanics 788 (22 décembre 2015) : 183–208. http://dx.doi.org/10.1017/jfm.2015.674.
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We investigate the vibration properties of a circular horizontal film that is bounded by a meniscus (or Plateau border) and suspended between two catenary films. The suspending films act as capillary springs, and the system is thus free to oscillate around its equilibrium position. We study its free and forced oscillations. In our experiments, we track simultaneously the positions of the Plateau border and the film. The model that we present predicts the eigenfrequency of the system and its resonance characteristics (in forced oscillations). In particular, we show that the dynamics of both the Plateau border and the film have to be taken into account in order to provide an accurate prediction of the oscillation frequency.
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Llewellin, E. W., E. Del Bello, J. Taddeucci, P. Scarlato et S. J. Lane. « The thickness of the falling film of liquid around a Taylor bubble ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 468, no 2140 (7 décembre 2011) : 1041–64. http://dx.doi.org/10.1098/rspa.2011.0476.
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We present the results of laboratory experiments that quantify the physical controls on the thickness of the falling film of liquid around a Taylor bubble, when liquid–gas interfacial tension can be neglected. We find that the dimensionless film thickness λ ′ (the ratio of the film thickness to the pipe radius) is a function only of the dimensionless parameter , where ρ is the liquid density, g the gravitational acceleration, D the pipe diameter and μ the dynamic viscosity of the liquid. For , the dimensionless film thickness is independent of N f with value λ ′≈0.33; in the interval , λ ′ decreases with increasing N f ; for film thickness is, again, independent of N f with value λ ′≈0.08. We synthesize existing models for films falling down a plane surface and around a Taylor bubble, and develop a theoretical model for film thickness that encompasses the viscous, inertial and turbulent regimes. Based on our data, we also propose a single empirical correlation for λ ′( N f ), which is valid in the range 10 −1 < N f <10 5 . Finally, we consider the thickness of the falling film when interfacial tension cannot be neglected, and find that film thickness decreases as interfacial tension becomes more important.
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Stumpf, Bastian, Jeanette Hussong et Ilia V. Roisman. « Drop Impact onto a Substrate Wetted by Another Liquid : Flow in the Wall Film ». Colloids and Interfaces 6, no 4 (20 octobre 2022) : 58. http://dx.doi.org/10.3390/colloids6040058.
Texte intégralRésumé :
The impact of a drop onto a liquid film is relevant for many natural phenomena and industrial applications such as spray painting, inkjet printing, agricultural sprays, or spray cooling. In particular, the height of liquid remaining on the substrate after impact is of special interest for painting and coating but also for applications involving heat transfer from the wall. While much progress has been made in explaining the hydrodynamics of drop impact onto a liquid film of the same liquid, the physics of drop impact onto a wall film with different material properties is still not well understood. In this study, drop impact onto a very thin liquid film of another liquid is investigated. The thickness of the film remaining on a substrate after drop impact is measured using a chromatic-confocal line sensor. It is interesting that the residual film thickness does not depend on the initial thickness of the wall film, but strongly depends on its viscosity. A theoretical model for the flow in the drop and wall film is developed which accounts for the development of viscous boundary layers in both liquids. The theoretical predictions agree well with the experimental data.
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Pavlenko, Ivan, Oleksandr Liaposhchenko, Marek Ochowiak, Radosław Olszewski, Maryna Demianenko, Oleksandr Starynskyi, Vitalii Ivanov, Vitalii Yanovych, Sylwia Włodarczak et Michał Doligalski. « Three-Dimensional Mathematical Model of the Liquid Film Downflow on a Vertical Surface ». Energies 13, no 8 (15 avril 2020) : 1938. http://dx.doi.org/10.3390/en13081938.
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Film downflow from captured liquid without wave formation and its destruction is one of the most important aspects in the development of separation equipment. Consequently, it is necessary to create well-organized liquid draining in areas of captured liquid. Thus, the proposed 3D mathematical model of film downflow allows for the determination of the hydrodynamic parameters of the liquid film flow and the interfacial surface. As a result, it was discovered that the interfacial surface depends on the proposed dimensionless criterion, which includes internal friction stress, channel length, and fluid density. Additionally, equations for determining the averaged film thickness, the averaged velocity vectors over the film thickness, the longitudinal and vertical velocity components, and the initial angle of streamline deviation from the vertical axis were analytically obtained.
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Li, Chengxian, et Shengguo Xia. « Study on Lubrication Characteristics of Metal Liquid Film Based on Electromagnetic-Elastic Mechanics-Hydrodynamics Multiphysics Coupling Model ». Materials 13, no 5 (27 février 2020) : 1056. http://dx.doi.org/10.3390/ma13051056.
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In an electromagnetic rail launcher, a metal liquid film is created at the armature/rail (A/R) contact interface. It has a significant impact on electromagnetic launch performance. In this paper, an electromagnetic-elastic mechanics-hydrodynamics multi physics coupling model is established in consideration of the metal liquid film’s own acceleration, magnetic pressure and dynamic changes in film thickness. Based on this model, the lubricating characteristics of magnetic pressure and fluid pressure distribution, film thickness distribution and velocity distribution of the metal liquid film were studied. When the velocity of the metal liquid film is very fast, and the magnetic pressure is reduced, it may fail to maintain stability and rupture, which may be an important reason for the transition. Finally, this paper analyzes the lubrication effect of the metal liquid film, and points out that when we want strictly to control the muzzle velocity, the lubrication effect of the metal liquid film must be considered.
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Wan, Zhihua, Ping Wang, Huanying Shen et Yanzhong Li. « Falling Film Flow and Heat Transfer of Cryogenic Liquid Oxygen on Different Structural Surfaces ». Energies 15, no 14 (10 juillet 2022) : 5040. http://dx.doi.org/10.3390/en15145040.
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The accurate prediction of the falling film characteristics of cryogenic liquids is necessary to ensure good evaporation performance, due to their special physical properties. In this study, the film flow and heat transfer characteristics on four different structures were investigated, and the performance of the cryogenic liquid oxygen was compared with other fluids with higher temperatures, which demonstrates the influence of structures and liquid mediums. The VOF model was used to capture the film surface in the simulation model. The results show that for the four structures, liquids with higher kinematic viscosity tend to have greater film thickness, and the sensible heat transfer coefficients are inversely related to the nominal thermal resistance of falling film flow. Both on the smooth plate and the corrugated plate, the film wettability depends on the kinematic viscosity, rather than the dynamic viscosity, and the effect of kinematic viscosity is greater than that of surface tension. Both the local heat transfer coefficient and its fluctuation amplitude decrease gradually along the flow direction on the triangular corrugated plate, and the vortices are easier to produce at the wall troughs when the film viscosity is higher. At the bottom of the horizontal tube, the increases in local film thickness of the liquid oxygen are less than those of the water and the seawater. More liquid tends to accumulate at the bottom of the round tube, while it easily detaches from the film surface of the elliptical tube. For the horizontal tubes, the local heat transfer coefficients decrease rapidly when θ = 0–5°, and increase sharply at θ = 175–180°.
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Li, Jia-Xin, Yun-Ze Li, En-Hui Li et Tong Li. « Numerical Investigation on the Thermodynamic Characteristics of a Liquid Film upon Spray Cooling Using an Air-Blast Atomization Nozzle ». Entropy 22, no 3 (9 mars 2020) : 308. http://dx.doi.org/10.3390/e22030308.
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This paper developed a three-dimensional model to simulate the process of atomization and liquid film formation during the air-blast spray cooling technological process. The model was solved using the discrete phase model method. Several factors including the thermodynamic characteristics of the liquid film as well as the spray quality with different spray mass flow rates under different spray heights were numerically investigated and discussed. The results show that the varied spray height has little effect on the Sauter Mean Diameter (d32) of the spray droplet, while the thermodynamic characteristics of liquid film including the liquid film height, the liquid film velocity, and the liquid film generation rate are sensitive to the change of the spray height. With the growth of spray mass flow rates, d32, the liquid film generation rate and liquid film height become larger, while the liquid film velocity with different spray mass flow rates has a similar velocity distribution, indicating that the spray mass flow rate has little effect on the liquid film velocity. The average d32 of droplet size shows a sharp drop when sprayed from the nozzle in a short period of time (<1.5 ms), then approaching smoothness, below a value of 40 μ m , the spray status tends to be stable.
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Xu, Fei, Yaning Zhang, Guangri Jin, Bingxi Li, Yong-Song Kim, Gongnan Xie et Zhongbin Fu. « Three phase heat and mass transfer model for unsaturated soil freezing process : Part 1 - model development ». Open Physics 16, no 1 (2 avril 2018) : 75–83. http://dx.doi.org/10.1515/phys-2018-0014.
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Abstract A three-phase model capable of predicting the heat transfer and moisture migration for soil freezing process was developed based on the Shen-Chen model and the mechanisms of heat and mass transfer in unsaturated soil freezing. The pre-melted film was taken into consideration, and the relationship between film thickness and soil temperature was used to calculate the liquid water fraction in both frozen zone and freezing fringe. The force that causes the moisture migration was calculated by the sum of several interactive forces and the suction in the pre-melted film was regarded as an interactive force between ice and water. Two kinds of resistance were regarded as a kind of body force related to the water films between the ice grains and soil grains, and a block force instead of gravity was introduced to keep balance with gravity before soil freezing. Lattice Boltzmann method was used in the simulation, and the input variables for the simulation included the size of computational domain, obstacle fraction, liquid water fraction, air fraction and soil porosity. The model is capable of predicting the water content distribution along soil depth and variations in water content and temperature during soil freezing process.
24
Zemitis, A. « ON INTERACTION OF A LIQUID FILM WITH AN OBSTACLE ». Mathematical Modelling and Analysis 7, no 2 (15 décembre 2002) : 327–42. http://dx.doi.org/10.3846/13926292.2002.9637204.
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In this paper are discussed mathematical models for the liquid film generated by impinging jets. These models describe only the film shape under special assumptions about processes. Attention is stressed on the interaction of the liquid film with some obstacle. The idea is to generalize existing models and to investigate qualitative behavior of liquid film using numerical experiments. G.I. Taylor [Proc. R. Soc. London Ser. A 253, 313 (1959)] found that the liquid film generated by impinging jets is very sensitive to properties of the wire which was used as an obstacle. The aim of this presentation is to propose a modification of the Taylor's model, which allows to simulate the film shape in cases when the angle between jets is different from 180°. Numerical results obtained by discussed models give two different shapes of the liquid film similar as in Taylors experiments. These two shapes depend on the regime: either droplets are produced close to the obstacle or not. The difference between two regimes becomes larger if the angle between jets decreases. Existence of such two regimes can be very essential for some applications of impinging jets, if the generated liquid film can have a contact with obstacles.
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Kaewthong, Jutarat, Wuttipan Satienpaisan, Natthawat Hongkarnjanakul, Padetha Tin et Nattaporn Chattham. « Coalescence of nematic liquid crystal droplets on freely suspended liquid crystal films ». Journal of Physics : Conference Series 2431, no 1 (1 janvier 2023) : 012067. http://dx.doi.org/10.1088/1742-6596/2431/1/012067.
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Abstract Freely suspended smectic films of a few molecular layers thick is a model system that can be used to study two dimensional phenomena. In our study, we drew a smectic C film across a few millimeter hole and stabilized it with a strong surface tension capable of suspending 5CB nematic liquid crystal droplets sprayed onto it. Thermal fluctuation of liquid crystal molecules is observed across the smectic C film and can cause the droplets to be driven closer and coalesce. The coalescence in this environment has yet to be studied more extensively. When two droplets are touching each other, connecting bridge between them forms and rapidly grows while they merge. Coalescence between them was thoroughly studied through high-speed camera under the cross-polarized observation and different regimes during coalescence process were analysed. Scaling law for various regimes will be discussed and explained. To understand the experimental result further, we also perform the study of droplet coalescence through finite element software which include inertial force, interfacial force and viscous force in the model. Comparing and analyzing the experimental and simulation results.
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A. Kuibin, Pavel, et Oleg V. Sharypov. « Vortex Generation in a Thin Liquid Layer under the Effect of Moving Heater ». Siberian Journal of Physics 3, no 2 (1 juillet 2008) : 40–46. http://dx.doi.org/10.54362/1818-7919-2008-3-2-40-46.
Texte intégralRésumé :
An effect of moving local heater on the flow structure in a thin liquid layer on horizontal substrate is analyzed. The 2-D problem is considered under boundary layer approximation. For the case of small Reynolds numbers the steadystate equation is derived for description of the liquid film deformation in the accompanying frame of reference. The obtained equation can be applied in particular at horizontal substrate orientation. The results of simulations of the film thickness, pressure and liquid velocity at a given model temperature distribution on a free surface are presented. The dependencies of liquid viscosity and density on the temperature are neglected in the model, as well as heat, mass and momentum transfer at the free surface. It is shown that even in absence of liquid motion under gravity action the motion of local heater provides the existence of steady-state regime without film breakdown and dry spot formation. As outcome the theoretical background for new scheme of experimental study of phenomena in non-isothermal liquid films is developed.
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Edwards, Andrew M. J., Rodrigo Ledesma-Aguilar, Michael I. Newton, Carl V. Brown et Glen McHale. « Not spreading in reverse : The dewetting of a liquid film into a single drop ». Science Advances 2, no 9 (septembre 2016) : e1600183. http://dx.doi.org/10.1126/sciadv.1600183.
Texte intégralRésumé :
Wetting and dewetting are both fundamental modes of motion of liquids on solid surfaces. They are critically important for processes in biology, chemistry, and engineering, such as drying, coating, and lubrication. However, recent progress in wetting, which has led to new fields such as superhydrophobicity and liquid marbles, has not been matched by dewetting. A significant problem has been the inability to study the model system of a uniform film dewetting from a nonwetting surface to a single macroscopic droplet—a barrier that does not exist for the reverse wetting process of a droplet spreading into a film. We report the dewetting of a dielectrophoresis-induced film into a single equilibrium droplet. The emergent picture of the full dewetting dynamics is of an initial regime, where a liquid rim recedes at constant speed and constant dynamic contact angle, followed by a relatively short exponential relaxation of a spherical cap shape. This sharply contrasts with the reverse wetting process, where a spreading droplet follows a smooth sequence of spherical cap shapes. Complementary numerical simulations and a hydrodynamic model reveal a local dewetting mechanism driven by the equilibrium contact angle, where contact line slip dominates the dewetting dynamics. Our conclusions can be used to understand a wide variety of processes involving liquid dewetting, such as drop rebound, condensation, and evaporation. In overcoming the barrier to studying single film-to-droplet dewetting, our results provide new approaches to fluid manipulation and uses of dewetting, such as inducing films of prescribed initial shapes and slip-controlled liquid retraction.
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Agati, Giuliano, Adriano Evangelisti, Serena Gabriele, Franco Rispoli, Paolo Venturini et Domenico Borello. « Liquid film formation : prediction accuracy of different numerical approaches ». Journal of Physics : Conference Series 2385, no 1 (1 décembre 2022) : 012138. http://dx.doi.org/10.1088/1742-6596/2385/1/012138.
Texte intégralRésumé :
Abstract In counteracting fouling phenomenon in gas turbines, which leads to system inefficiencies and performance degradation, water washing technique is very often adopted. Water droplets sprays are injected and, hitting the solid surfaces, remove the dirt deposition. Among the collateral undesirable phenomena related to water washing, blades erosion and liquid film formation are the most remarkable. Despite the former issue was extensively assessed by the authors in previous works, up to the authors’ knowledge the risk of liquid film formation due to water washing was scarcely investigated. Liquid film formation and spreading on a solid surface is a complex phenomenon involving a large number of physical events, such as: droplets impact on a solid surface, splashing phenomena, liquid film dragging under the effect of the carrier phase and droplets separation from the film in proximity of geometry discontinuities. In this paper, an extensively used experimental test case involving all these phenomena was used to test different numerical wall film models available in literature. The test case consists in the injection of a liquid jet in a high velocity crossflow. Some of the liquid jet mass impacts on the opposite solid surface generating a wall film which develops under the dragging effect of the crossflow. A Lagrangian approach was used to track the suspended droplets within the flow field by also considering the turbulent dispersion by means of a Random Walk model. Droplets-wall interaction is considered according to the Stanton-Rutland model, which provides the outcome of a collision (deposit, rebound or splashing), depending on the local impact conditions. If a droplet sticks on a solid boundary, a liquid film generates. Droplets atomization is also accounted for by using the Madabhushi model while Friederich separation model was selected to take into account the detachment of droplets from the film at the geometry edge. Three different numerical simulations have been performed based on different approaches used to solve the liquid film evolution, namely Eulerian one-way coupling, Eulerian two-way coupling and Lagrangian two-way coupling. Numerical results have been compared with the experimental ones from both a qualitative and a quantitative point of view. The wall film shape, its spatial distribution and the variation of the film thickness of the wall centreline have been compared between experimental and numerical simulations proving that the Lagrangian 2-way coupling approach better reproduces the liquid film dynamics observed in the experiments.
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Lozowski, E. P., A. M. Kobos et L. G. Kachurin. « Influence of the Surface Liquid Film on Cylinder Icing Under Marine Conditions ». Journal of Offshore Mechanics and Arctic Engineering 118, no 2 (1 mai 1996) : 158–64. http://dx.doi.org/10.1115/1.2828826.
Texte intégralRésumé :
A new steady-state icing model is presented Which explicitly takes into account the dynamics and thermodynamics of a liquid film on the ice accretion surface under high liquid fluxes. The film is generated by excess unfrozen impinging liquid, is set in motion by the aerodynamic shear stress, and is eventually shed. In order to keep the model simple, it is formulated for a rotating cylinder subjected to a continuous supercooled freshwater spray. The model is used to explore the physics of the liquid film, and confirms that the film is thin and laminar except possibly under extreme liquid fluxes. It predicts supercooling of several degrees at the film surface, in agreement with recent observations. Further, the model is used to investigate the dependence of the icing rate on the following parameters: liquid water content, air temperature, wind speed, spray temperature, cylinder diameter, and heat transfer coefficient.
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Fan, Yilin, Eduardo Pereyra et Cem Sarica. « Onset of Liquid-Film Reversal In Upward-Inclined Pipes ». SPE Journal 23, no 05 (11 mai 2018) : 1630–47. http://dx.doi.org/10.2118/191120-pa.
Texte intégralRésumé :
Summary Accumulation of oil and/or water at the bottom of an upward-inclined pipe is known to be the source of many industrial problems, such as corrosion and terrain slugging. Therefore, accurate prediction of the critical gas velocity that can avoid the liquid accumulation is of great importance. An experimental study of onset of liquid-film reversal, which is believed to be the main cause of liquid accumulation, was conducted in a hilly-valley test section at low-liquid-loading condition. A new, easily implemented mechanistic model to predict critical gas velocity, which is specifically developed based on the liquid-film reversal in stratified flow, is proposed in this work. The new model was verified with the data acquired in the study and other studies from the open literature, showing a fair agreement. This work also reviewed and evaluated other critical-gas-velocity-prediction models. The new model performs best compared with other models, especially in terms of the inclination angle and liquid-flow-rate effect on critical gas velocity. The total average absolute error was reduced 6.0% compared with the current best-prediction model (Zhang et al. 2003), and 38.2% for the widely used Turner et al. (1969) droplet-removal model.
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Roque, Anthony, Fabrice Foucher, Quentin Lamiel, Bill Imoehl, Nicolas Lamarque et Jerome Helie. « Impact of gasoline direct injection fuel films on exhaust soot production in a model experiment ». International Journal of Engine Research 21, no 2 (7 octobre 2019) : 367–90. http://dx.doi.org/10.1177/1468087419879851.
Texte intégralRésumé :
The fuel films that can be generated during the injection process in gasoline direct injection engines are the most important factor in carbon particle mass and number. They also have an influence on combustion chamber and injector tip deposits. A model experiment was set up to study a liquid film, its evaporation, and combustion with soot generation on a metal plate in realistic engine conditions. The experiment was conducted in a dedicated constant volume vessel. A liquid fuel injection system (with injection pressures up to 100 bar) directs the spray onto a plate with a controlled temperature in the range of 80 °C–200 °C. The resulting liquid film and vaporization process were studied when subjected to interaction with a laminar spherical flame. A blend of four components was used as a gasoline surrogate. The liquid film spreading, thickness, and evaporation rates were initially measured in ambient conditions. Mie scattering and schlieren measurements in the chamber conditions returned a qualitative correlation of the vaporized area with the surface temperature. Fluorescence of the light and heavy fuel components was used to quantify the influence of the vaporization process on soot production. Simultaneous measurements of natural luminosity and KL factor were analyzed to understand the process of soot production. The results showed a critical wall temperature of 120 °C at which the maximum quantity of soot is generated, which can be due to the quantity and composition of fuel film in interaction with the entrainment flows generated during combustion.
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Grishaev, Viktor G., Ivan K. Bakulin, Alidad Amirfazli et Iskander S. Akhatov. « Puncture of a Viscous Liquid Film Due to Droplet Falling ». Fluids 7, no 6 (8 juin 2022) : 196. http://dx.doi.org/10.3390/fluids7060196.
Texte intégralRésumé :
Droplet impact may rupture a liquid film on a non-wettable surface. The formation of a stable dry spot has only been studied in the inviscid case. Here, we examine the break-up of viscous films, and demonstrate the importance and role of the viscous dissipation in both film and droplet. A new model was therefore proposed to predict the necessary droplet energy to create a dry spot. It also showed that the dissipation contribution in film dominates when the ratio of the thicknesses to drop diameter is larger than 7/4.
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Chen, C., P. Joseph, S. Geoffroy, M. Prat et P. Duru. « Evaporation with the formation of chains of liquid bridges ». Journal of Fluid Mechanics 837 (5 janvier 2018) : 703–28. http://dx.doi.org/10.1017/jfm.2017.827.
Texte intégralRésumé :
The objective of the present work is to study the drying of a quasi-two-dimensional model porous medium, hereafter called the micromodel, initially filled with a pure liquid. The micromodel consists of cylinders measuring $50~\unicode[STIX]{x03BC}\text{m}$ in both height and diameter, radially arranged as a set of neighbouring spirals and sandwiched between two horizontal flat plates. As drying proceeds, air invades the pore space and elongated liquid films trapped by capillary forces form along the spirals. These films consist of ‘chains’ of liquid bridges connecting neighbouring cylinders. They provide hydraulic connectivity between the central bulk liquid cluster and the external rim of the cylinder pattern, where evaporation takes place during a first constant-evaporation-rate drying stage. The first goal of the present paper is to describe experimentally the phase distribution during drying, notably the evolution of liquid films, which controls the evaporation kinetics (e.g. the depinning of the films from the external rim signals the end of the constant-evaporation-rate period). Then, a viscocapillary model for the drying process is presented. It is based on numerical simulations of a liquid film capillary shape and viscous flow within a film. The model shows a reasonably good agreement with the experimental data. Thus, the present study is a step towards direct modelling of the effect of films on the drying of more complex porous media (e.g. packing of beads) and should be of interest for multiphase flow applications in porous media, involving transport within liquid films.
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Wu, Rui, et Feng Chen. « Interplay between salt precipitation, corner liquid film flow, and gas–liquid displacement during evaporation in microfluidic pore networks ». Journal of Applied Physics 133, no 7 (21 février 2023) : 074701. http://dx.doi.org/10.1063/5.0135135.
Texte intégralRésumé :
Visualization experiments with microfluidic pore networks are performed in this work to disclose interplay between salt precipitation, the corner liquid film flow, and gas–liquid displacement during evaporation. Two forms of salt precipitation are revealed: aggregated polycrystalline structures and large bulk crystals. It is found that gas bubbles can be formed because of imbibition of liquid into aggregated polycrystalline structures. The length of a corner liquid film can affect the direction of growth of the aggregated polycrystalline structures connected to the corner liquid film. Discontinuous corner liquid films can be transformed to continuous ones when they are touched by growing aggregated polycrystalline structures. The “sleeping” aggregated polycrystalline structures at the open surface of a microfluidic pore network, i.e., efflorescence, can grow again if they are touched by growing aggregated polycrystalline structures inside the microfluidic pore network, i.e., subflorescence. Because of efflorescence, the evaporation rate from a microfluidic pore network can increase first and then decrease. Moreover, a theoretical model is developed for the coupled transport of vapor diffusion in the gas zone and liquid flow as well as transport of dissolved salt in the corner liquid films in a capillary tube of square cross section so as to disclose the key parameters controlling the transport processes.
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Wajs, Jan, et Dariusz Mikielewicz. « Determination of dryout localization using a five-equation model of annular flow for boiling in minichannels ». Archives of Thermodynamics 38, no 1 (28 mars 2017) : 123–39. http://dx.doi.org/10.1515/aoter-2017-0007.
Texte intégralRésumé :
AbstractDetailed studies have suggested that the critical heat flux in the form of dryout in minichannels occurs when the combined effects of entrainment, deposition, and evaporation of the film make the film flow rate go gradually and smoothly to zero. Most approaches so far used the mass balance equation for the liquid film with appropriate formulations for the rate of deposition and entrainment respectively. It must be acknowledged that any discrepancy in determination of deposition and entrainment rates, together with cross-correlations between them, leads to the loss of accuracy of model predictions. Conservation equations relating the primary parameters are established for the liquid film and vapor core. The model consists of three mass balance equations, for liquid in the film as well as two-phase core and the gas phase itself. These equations are supplemented by the corresponding momentum equations for liquid in the film and the two-phase core. Applicability of the model has been tested on some experimental data.
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Dietze, Georg F., et Christian Ruyer-Quil. « Films in narrow tubes ». Journal of Fluid Mechanics 762 (27 novembre 2014) : 68–109. http://dx.doi.org/10.1017/jfm.2014.648.
Texte intégralRésumé :
AbstractWe consider the axisymmetric arrangement of an annular liquid film, coating the inner surface of a narrow cylindrical tube, in interaction with an active core fluid. We introduce a low-dimensional model based on the two-phase weighted residual integral boundary layer (WRIBL) formalism (Dietze & Ruyer-Quil, J. Fluid Mech., vol. 722, 2013, pp. 348–393) which is able to capture the long-wave instabilities characterizing such flows. Our model improves upon existing works by fully representing interfacial coupling and accounting for inertia as well as streamwise viscous diffusion in both phases. We apply this model to gravity-free liquid-film/core-fluid arrangements in narrow capillaries with specific attention to the dynamics leading to flooding, i.e. when the liquid film drains into large-amplitude collars that occlude the tube cross-section. We do this against the background of linear stability calculations and nonlinear two-phase direct numerical simulations (DNS). Due to the improvements of our model, we have found a number of novel/salient physical features of these flows. First, we show that it is essential to account for inertia and full interphase coupling to capture the temporal evolution of flooding for fluid combinations that are not dominated by viscosity, e.g. water/air and water/silicone oil. Second, we elucidate a viscous-blocking mechanism which drastically delays flooding in thin films that are too thick to form unduloids. This mechanism involves buckling of the residual film between two liquid collars, generating two very pronounced film troughs where viscous dissipation is drastically increased and growth effectively arrested. Only at very long times does breaking of symmetry in this region (due to small perturbations) initiate a sliding motion of the liquid film similar to observations by Lister et al. (J. Fluid Mech., vol. 552, 2006, pp. 311–343) in thin non-flooding films. This kickstarts the growth of liquid collars anew and ultimately leads to flooding. We show that streamwise viscous diffusion is essential to this mechanism. Low-frequency core-flow oscillations, such as occur in human pulmonary capillaries, are found to set off this sliding-induced flooding mechanism much earlier.
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Morozov, Matvey, et Ofer Manor. « An extended Landau–Levich model for the dragging of a thin liquid film with a propagating surface acoustic wave ». Journal of Fluid Mechanics 810 (25 novembre 2016) : 307–22. http://dx.doi.org/10.1017/jfm.2016.728.
Texte intégralRésumé :
In this paper we revisit the Landau and Levich analysis of a coating flow in the case where the flow in the thin liquid film is supported by a Rayleigh surface acoustic wave (SAW), propagating in the solid substrate. Our theoretical analysis reveals that the geometry of the film evolves under the action of the propagating SAW in a manner that is similar to the evolution of films that are being deposited using the dip coating technique. We show that in a steady state the thin-film evolution equation reduces to a generalized Landau–Levich equation with the dragging velocity, imposed by the SAW, depending on the local film thickness. We demonstrate that the generalized Landau–Levich equation has a branch of stable steady state solutions and a branch of unstable solutions. The branches meet at a saddle-node bifurcation point corresponding to the threshold value of the SAW intensity. Below the threshold value no steady states were found and our numerical computations suggest a gradual thinning of the liquid film from its initial geometry.
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JOO, SANG W., STEPHEN H. DAVIS et S. GEORGE BANKOFF. « A simple hydrodynamic model for transition boiling ». Journal of Fluid Mechanics 402 (10 janvier 2000) : 195–210. http://dx.doi.org/10.1017/s0022112099006758.
Texte intégralRésumé :
A vertical column of an inviscid fluid, heated uniformly from below through a horizontal rigid bottom, is studied, with focus on the dynamics of the vapour/liquid interface near the three-phase (contact) line. The interfacial motion is induced by the competing effects of liquid feeding from above and evaporative mass loss through the interface. A linearized solution is obtained that describes the location of the contact line. The solution is used to study the transition processes to and from film boiling, where part of the liquid, lying on top of a vapour layer, can spontaneously be drawn downward and touch the heated bottom. Recession or advancement of the contact line then determines whether the film boiling is sustained or broken. It is seen that the correct contact-line dynamics cannot be predicted solely from a global mass balance in the liquid column.
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Maroteaux, F., D. Llory, J.-F. Le Coz et C. Habchi. « Liquid Film Atomization on Wall Edges—Separation Criterion and Droplets Formation Model ». Journal of Fluids Engineering 124, no 3 (19 août 2002) : 565–75. http://dx.doi.org/10.1115/1.1493811.
Texte intégralRésumé :
In order to predict the fuel mixture preparation inside the cylinder of port fuel injection engines, a model for the aerodynamic stripping of the fuel film deposited on the manifold walls is discussed, and a model for the fuel film separation and atomization near the sharp edges is developed. A separation criterion is set up using an analogy with Rayleigh-Taylor instabilities driven by the inertial forces of the liquid film. To determine the physical parameters of the resulting droplets, a liquid sheet atomization scheme is used. The critical value for the separation criterion is adjusted using experimental data obtained in 2D wind tunnel equipped with different steps shaped as a valve seat, and reproducing the main characteristics of the intake of spark ignition engine. CFD simulations are performed using the KMB code, a modified version of KIVA-2 already including a stochastic Lagrangian description of the spray, and an Eulerian liquid film model. Computations results for different operating conditions are in good agreement with the images of film separation and measured droplet size distributions.
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Wang, Yun-lei, Jiu-hui Wu, Zhen-tao Li et Lu-shuai Xu. « Effect of slip position on the hydrodynamic performance of liquid film seal ». Industrial Lubrication and Tribology 73, no 3 (19 novembre 2020) : 405–13. http://dx.doi.org/10.1108/ilt-03-2020-0082.
Texte intégralRésumé :
Purpose The purpose of this paper is to investigate the effect of slip position on the performance of liquid film seal. Design/methodology/approach A mathematical model of liquid film seal with slip/no-slip surface was established based on the Navier slip model and JFO boundary condition. Liquid film governing equation was discretized by the finite difference method and solved by the SOR relaxation iterative algorithm and the effects of slip position on sealing performance are discussed. Findings The results indicate that boundary slip plays an important role in the overall performance of a seal and a reasonable arrangement of slip position can improve the steady-state performance of liquid film seal. Originality/value Based on the mathematical model, the optimal parameters for liquid film seal with boundary slip at groove are obtained. The results presented in this study are expected to provide a theoretical basis to improve the design method of liquid film seal. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2020-0082/
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Zhang, Jun Xia, et Xiao Lin Xu. « Application of VOF Interfacial Tracking Model to Condensation Heat Transfer ». Advanced Materials Research 619 (décembre 2012) : 139–42. http://dx.doi.org/10.4028/www.scientific.net/amr.619.139.
Texte intégralRésumé :
Condensation heat transfer used to the condenser as an important way of heat transfer is a phenomenon that involves flowing and heat and mass transfer of both gas and liquid phases. Thus, the development of its numerical prediction helps to the design of the condenser. At the present work, a VOF model was used to numerically simulate condensation heat transfer in a V-shape tube, obtaining volume fraction of vapor, location of liquid film and parameters of heat transfer. Results show that the VOF model may predict flow pattern of condensation and mass flux of condensation of vapor on the liquid film well. From computations, mass flux of condensation of vapor on the liquid film increases along vapor flowing, however, it tends to steady at the back part of the condenser tube. Flow pattern of condensation develops from annular flow at the inlet of the condenser tube to stratified flow, finally to plug flow at its back part. Velocity decreases along the tube length.
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Gerendas, M., et S. Wittig. « Experimental and Numerical Investigation on the Evaporation of Shear-Driven Multicomponent Liquid Wall Films ». Journal of Engineering for Gas Turbines and Power 123, no 3 (1 janvier 2001) : 580–88. http://dx.doi.org/10.1115/1.1362663.
Texte intégralRésumé :
The presented work is concerned with two-phase flows similar to those in prefilming airblast atomizers and combustors employing film vaporization. Correlations for the multicomponent mixture properties and models for the calculations of the multicomponent evaporation were implemented in a well tested elliptic finite-volume code GAP-2D (S. Wittig et al., 1992, “Motion and Evaporation of Shear-Driven Liquid Films in Turbulent Gas,” ASME J. Eng. Gas Turbines Power 114, pp. 395–400) utilizing time-averaged quantities, k,ε turbulence model, wall functions, and curve-linear coordinates in the gas phase, adiabatic or diabatic conditions at the film plate, partially turbulent velocity profile, uniform temperature, and a rapid mixing approach in the wavy film. This new code GAP-2K was tested for stability, precision, and grid independence of the results by applying it to a turbulent hot air flow over a two-component liquid film, a mixture of water and ethanol in different concentrations. Both simulations and experiments were carried out over a wide range of inlet conditions, such as inlet pressure (1–2.6 bar), inlet temperature (298–573 K), inlet air velocity (30–120 m/s), initial liquid flow rate (0.3–1.2 cm2/s), and initial ethanol concentration (20–75 percent mass). Profiles of temperature, gas velocity, and concentration of the evaporating component normal to the film, and the development of the film temperature, the static pressure, the liquid flow rate, and the liquid compound along the film plate have been measured and compared with the simulation, showing a good match.
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Wang, Yun-Lei, Jiu-Hui Wu, Mu-Ming Hao et Lu-Shuai Xu. « Improved hydrodynamic performance of liquid film seal by considering boundary slip and cavitation ». Industrial Lubrication and Tribology 71, no 9 (4 novembre 2019) : 1108–15. http://dx.doi.org/10.1108/ilt-03-2019-0088.
Texte intégralRésumé :
Purpose The purpose of this paper is to investigate the effect of boundary slip on hydrodynamic performance of liquid film seal considering cavitation. Design/methodology/approach A mathematical model of liquid film seal with slip surface was established based on the Navier slip model and Jakobsson–Floberg–Olsson (JFO) boundary condition. Liquid film governing equation was discretized by the finite difference method and solved by the SOR relaxation iterative algorithm and the hydrodynamic performance parameters of liquid film seal were obtained considering boundary slip and cavitation. Findings The results indicate that the values of performance parameters are affected significantly by the slip length under the condition of high speed and low differential pressure. Originality/value The performances of liquid film seal are investigated considering slip surface and cavitation. The results presented in the study are expected to provide a theoretical basis to improve the design method of liquid film seal.
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Lee Yeu, Yee, et Alexander Gorin. « Two-Phase Region Effect on Film Condensation on an Inclined Plate Embedded in a Porous Medium ». Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 78, no 2 (10 décembre 2020) : 67–84. http://dx.doi.org/10.37934/arfmts.78.2.6784.
Texte intégralRésumé :
Film condensation in a porous medium has been receiving increasing attention due to its wide range of heat transfer applications. Some examples of these practical applications are distillation, drying technology, geothermal energy, cooling towers, heat exchangers, and air conditioning. One of the characteristic features of film condensation in porous media is the formation of a two-phase zone separating the liquid film and the vapour zone due to capillary pressure. In this paper, a physico-mathematical model of liquid film condensation on a surface embedded in a porous medium with a two-phase region effect is developed and presented. The model is based on momentum and continuity equations as applied to the liquid film and the two-phase flow region supplemented with the Darcy flow assumption and assumptions on the Leverette J-function and the saturation behaviour near the edge of the liquid film. The developed model allows a simple analytical solution to the problem in distinction to semi-analytical and numerical solutions published by different authors. From the model developed, it shows that the presence of the two-phase region decreases the liquid film thickness. By taking the capillary effects into consideration results in higher heat transfer and condensation rates due to the decrease in the liquid film thickness. The presented model yields good agreement when compared to the theoretical results and experimental data by other authors. The developed model addresses the fundamental concepts of phase transition in porous media which can effectively find applications in many areas.
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Zhou, Yu, Yang Zou, Chao Gao, Qinwen Xu, Xin Tong, Binghui Lin, Yan Liu, Bo Woon Soon, Yao Cai et Chengliang Sun. « Investigation of film bulk acoustic resonators for sensing applications in liquid environment ». Applied Physics Letters 121, no 21 (21 novembre 2022) : 213501. http://dx.doi.org/10.1063/5.0124829.
Texte intégralRésumé :
The thin film bulk acoustic resonator (FBAR) has emerged as a promising choice for liquid sensors because of its high frequency and sensitivity. To investigate the potential of FBAR devices working as the liquid sensors, we study the operating law of FBAR in liquid environments and explore the different loading effects of liquid on the shear mode and longitudinal mode. By analyzing the device and liquid interactions, we modify the Mason model of FBAR in the liquid environment. Subsequently, the influence of the piezoelectric film with different tilt angles and liquids on the characteristics of FBAR is discussed. We also prepared Sc0.2Al0.8N film-based FBAR to confirm the influence of different liquid environments on the resonant performances. The results show that the frequency drift of FBAR in the shear mode is related to density and viscosity of liquid, and the frequency drift of FBAR in the longitudinal mode is related to bulk modulus and density of liquid. The resonant frequency of FBAR in the shear mode is more sensitive with glycerol solution than that of FBAR in the longitudinal mode. This work can provide a research basis for the application of FBAR liquid sensors.
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Zhang, Hong-Quan, et Cem Sarica. « A Model for Wetted-Wall Fraction and Gravity Center of Liquid Film in Gas/Liquid Pipe Flow ». SPE Journal 16, no 03 (16 juin 2011) : 692–97. http://dx.doi.org/10.2118/148330-pa.
Texte intégralRésumé :
Summary The model presented in this study unifies the predictions of liquid wetted-wall fraction, film gravity center, and flow-pattern transition between stratified and annular flows. It is based on the instability of the liquid film in an equilibrium stratified flow proposed by Taitel and Dukler (1976) for flow-pattern transition prediction from stratified flow to nonstratified flows. The geometrical relationship between the wetted-wall fraction and the gravity center of the liquid film is established based on the double-circle model proposed by Chen et al. (1997), and is further simplified with explicit approximation. The predictions of the present model are compared and agree well with experimental wetted-wall-fraction measurements and flow-pattern observations from different authors.
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Su, Shujing, Zihui Geng, Xiaoxin Ma, Qiulin Tan et Jijun Xiong. « A film bulk acoustic resonator pressure sensor based on lateral field excitation ». International Journal of Distributed Sensor Networks 14, no 11 (novembre 2018) : 155014771881434. http://dx.doi.org/10.1177/1550147718814343.
Texte intégralRésumé :
A high-sensitive thickness shear mode film bulk acoustic resonator pressure sensor based on lateral field excitation is designed with its structure simulated in environment of air and liquids. A finite element model of film bulk acoustic resonator pressure sensor structure is established to obtain frequency variation under different pressure conditions by parameter sweep method when the multi-physics fields are added to the model. The results of simulation show that the pressure sensor’s resonance frequency is 2.114 GHz and pressure sensitivity is 1200 Hz/kPa in air. In liquid environment, film bulk acoustic resonator pressure sensor displays a pressure sensitivity of 325 Hz/kPa in ethanol, 475 Hz/kPa in deionized water, and 612.5 Hz/kPa in glycerol. This film bulk acoustic resonator pressure sensor has been proved to be highly sensitive both in air and liquid environment and has the potential to be used in biomedical applications.
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Aursand, Eskil, Stephen H. Davis et Tor Ytrehus. « Thermocapillary instability as a mechanism for film boiling collapse ». Journal of Fluid Mechanics 852 (3 août 2018) : 283–312. http://dx.doi.org/10.1017/jfm.2018.545.
Texte intégralRésumé :
We construct a model to investigate the interfacial stability of film boiling, and discover that instability of very thin vapour films and subsequent large interface superheating is only possible if thermocapillary instabilities are present. The model concerns horizontal saturated film boiling, and includes novel features such as non-equilibrium evaporation based on kinetic theory, thermocapillary and vapour thrust stresses and van der Waals interactions. From linear stability analysis applied to this model, we are led to suggest that vapour film collapse depends on a balance between thermocapillary instabilities and vapour thrust stabilization. This yields a purely theoretical prediction of the Leidenfrost temperature. Given that the evaporation coefficient is in the range 0.7–1.0, this model is consistent with the average Leidenfrost temperature of every fluid for which data could be found. With an evaporation coefficient of 0.85, the model can predict the Leidenfrost point within 10 % error for every fluid, including cryogens and liquid metals where existing models and correlations fail.
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Yu, Xin Qi, Qing Gang Liu, Hui Qin Gao et Jia Hui Yu. « Liquid Film Performance Analysis of the Mechanical Seals with a Laser-Textured Micro-Pore Face ». Advanced Materials Research 139-141 (octobre 2010) : 418–21. http://dx.doi.org/10.4028/www.scientific.net/amr.139-141.418.
Texte intégralRésumé :
A theoretical model has been developed for the mechanical seals with a laser-textured porous seal face. By means of variable dimensionless steps, parametric analysis has been performed to obtain dimensionless liquid film pressure by the finite difference method. Liquid film pressure profiles over the pore column have be achieved by the computer program MATLAB. It is found from calculating results that average liquid film pressure increases with increase of the rotational speed, liquid viscosity and reduction of liquid film thickness. Hydrodynamic effect produced by micro-pores decreases with increase of fluid pressure. In addition, the effect of the pore area density and depth over diameter ratio on the liquid film pressure is very significant. Optimum values of these parameters can maximize the average liquid film pressure.
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Vikhansky, A. « An engineering model of a turbulent liquid film flow ». European Journal of Mechanics - B/Fluids 90 (novembre 2021) : 15–17. http://dx.doi.org/10.1016/j.euromechflu.2021.07.015.
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