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1
Pavlenko, Aleksandr, Oleg Volodin e Vladimir Serdyukov. "The Features Of The Film Flow Of Liquid Nitrogen Over The Structured Surfaces". Siberian Journal of Physics 10, n.º 1 (1 de março de 2015): 33–41. http://dx.doi.org/10.54362/1818-7919-2015-10-1-33-41.
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Experimental results on hydrodynamics of cryogenic liquid film flow over the surface of the single elements of the structured packing are presented. Based on the comparison of experimental data, the effect of microtexture and perforation on the zones of liquid film spreading over a corrugated surface is shown for different values of the film Reynolds number. The results of experiments on dependence of a relative portion of liquid held in a single irrigated channel of the corrugated plates with different thicknesses on irrigation degree are presented. It is shown that microtexture, its direction relative to the gravity has a significant effect on redistribution of the local flow rate of liquid flowing over the surface with complex geometry
2
Pavlenko, Aleksandr, Oleg Volodin e Vladimir Serdyukov. "Effect Of The Rib Inclination Angle On Liquid Film Spreading Over The Structured Surface". Siberian Journal of Physics 10, n.º 1 (1 de março de 2015): 42–49. http://dx.doi.org/10.54362/1818-7919-2015-10-1-42-49.
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Results of experimental studies on hydrodynamics of the film flow of liquid nitrogen over the surface of the single elements of structured packing are presented. The effect of inclination angle of the large ribs and perforation on the zones of liquid film spreading over the corrugated surface with microtexture at different Reynolds numbers of the film is shown based on a comparison of experimental data. It is shown that the angle of large rib inclination has a significant influence on redistribution of the local flow rate of liquid flowing on the surface with complex geometry. Analysis of results of the high-speed video revealed that in a vicinity of the vertical lateral edges of corrugated plates, the intense rivulet flows are formed, including those with separation from the film flow surface. This negative factor can lead to significant liquid accumulation and flow near the vertical edges of the structured packing and on the inner wall of the heat exchanging apparatuses and, finally, to a significant increase in the degree of maldistribution of local liquid flow rate over the crosssection, for instance, of the distillation columns.
3
Dressaire, Emilie, Laurent Courbin, Adrian Delancy, Marcus Roper e Howard A. Stone. "Study of polygonal water bells: inertia-dominated thin-film flows over microtextured surfaces". Journal of Fluid Mechanics 721 (13 de março de 2013): 46–57. http://dx.doi.org/10.1017/jfm.2013.60.
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AbstractMicrotextured surfaces are commonly used to study complex hydrodynamic phenomena such as spreading and splashing of liquid droplets. However, although surface topography is known to modify near-surface flow, there is no theory able to quantitatively predict the dramatic changes in dynamics of liquid spreading and splashing. Here, we investigate experimentally water bells formed on micropatterned surfaces in order to characterize the hydrodynamics of inertia-dominated flows through regular porous layers. Water bells are self-suspended catenary-shaped liquid films created when a jet impinges on a horizontal disc called an impactor. We show that the presence of micrometre-sized posts regularly arranged on the impactor results in a decrease of the water bell radius and the loss of axisymmetry as open water bells adopt polygonal shapes. We introduce a simple model that captures the main features of the inertia-dominated flow and reveals the role of the hydrodynamic interactions between neighbouring posts. In addition to their applications for tunable jet atomization, these polygonal sheets provide a paradigmatic system for understanding inertia-dominated flow in porous media.
4
Penn, David G., Martin Lopez de Bertodano, Paul S. Lykoudis e Stephen G. Beus. "Dry Patch Stability of Shear Driven Liquid Films". Journal of Fluids Engineering 123, n.º 4 (26 de junho de 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.
5
Silva, F. O., I. R. Siqueira, M. S. Carvalho e R. L. Thompson. "Slot coating flows with a Boussinesq–Scriven viscous interface". Physics of Fluids 35, n.º 4 (abril de 2023): 042106. http://dx.doi.org/10.1063/5.0147030.
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We present a computational study of free surface flows with rheologically complex interfaces in the film formation region of a slot coater. The equations of motion for incompressible Newtonian liquids in the bulk flow are coupled with the Boussinesq–Scriven constitutive equation for viscous interfaces in the dynamic boundary condition at the liquid-air free surface and solved with a mixed finite element method. We show that the interfacial viscosity plays a major role in the flow dynamics and operating limits of slot coating. We find that the interfacial viscosity makes viscous interfaces generally stiffer than their simple counterparts, affecting both the normal and the tangential stress jumps across the free surface. As a result, the interfacial viscosity counteracts the meniscus retraction and slows down the film flow, increasing the development length over the substrate and changing the topology of the recirculation region in the coating bead. Remarkably, we also find that the interfacial viscosity can substantially broaden the operating boundaries of the coating window associated with the low-flow limit, suggesting that surface-active components can be suitably designed to allow for the stable production of thinner films at higher speeds by tuning interfacial material properties in slot coating applications.
6
Pavlenko, Aleksandr, Anton Surtaev, Oleg Volodin e Vladimir Serdyukov. "Distribution Of Liquid Nitrogen At The Film Flow In The Single Elements Of The Structured Packing". Siberian Journal of Physics 11, n.º 2 (1 de junho de 2016): 12–20. http://dx.doi.org/10.54362/1818-7919-2016-11-2-12-20.
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Experimental results on the parameters of the film flow of cryogenic liquid over the surface of single elements of the structured packing consisting of two corrugated plates are presented. The effect of microtexture and its direction relative to the direction of gravity on liquid distribution along the packing at different irrigation degrees is shown based on the comparison with experimental data. Experimental results on the degree of liquid flowing through the contact points in the packing with plates are presented relative to the irrigation degree. It is shown that microtexture and its direction have a significant influence on redistribution of the local liquid flow, flowing on the structured surface of complex geometry, along the packing.
7
Shmyrov, Andrey. "Thermo-capillary flow in a Hele-Show cell as a tool for research of the dynamics of insoluble surfactant monolayer". EPJ Web of Conferences 213 (2019): 02073. http://dx.doi.org/10.1051/epjconf/201921302073.
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The occurrence of thermocapillary convection in a Hele-Shaw cell in the presence of the surfactant film on the free surface is experimentally investigated. It is shown that at certain values of the control parameter two different zones are formed on the surface – the zone free from impurities and the stagnant zone. In the first zone, the onset and development of an intense Marangoni convection is observed, while in the stagnant zone the velocity of the motion on the surface is lower by about two orders of magnitude. This study clearly demonstrates that the analysis of the temperature profile provides sufficient information about both the distribution of tangential stresses over the surface and the degree of compression of the surfactant film. In addition, due to a simple linear law of temperature variation on the surface of the stagnant zone, the distribution of the surfactant molecules over the surface can be predicted based on the known equation of state for the film of the examined surfactant. Thus, the application of a set of simple experimental techniques to the examined model problem allowed us to obtain complete information on the state of a complex system consisting of a liquid layer and a surface film of the surfactant, the structure of the volumetric flow, the velocity of the liquid at the surface, the distribution of shear stresses and surfactant molecules over the surface.
8
Dietze, Georg F., W. Rohlfs, K. Nährich, R. Kneer e B. Scheid. "Three-dimensional flow structures in laminar falling liquid films". Journal of Fluid Mechanics 743 (4 de março de 2014): 75–123. http://dx.doi.org/10.1017/jfm.2013.679.
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AbstractFull numerical simulations of the Navier–Stokes equations for four cases of vertically falling liquid films with three-dimensional surface waves have been performed. Flow conditions are based on several previous experimental studies where the streamwise and spanwise wavelengths were imposed, which we exploit by simulating periodic wave segments. The considered flows are laminar but approach conditions at which intermittent wave-induced turbulence has been observed elsewhere. Working liquids range from water to silicone oil and cover a large interval of the Kapitza number ($\textit {Ka}=18\mbox{--}3923$), which relates capillary to viscous forces. Simulations were performed on a supercomputer, using a finite-volume code and the volume of fluid and continuum surface force methods to account for the multiphase nature of the flow. Our results show that surface waves, consisting of large horseshoe-shaped wave humps concentrating most of the liquid and preceded by capillary ripples on a thin residual film, segregate the flow field into two regions: an inertia-dominated one in the large humps, where the local Reynolds number is up to five times larger than its mean value, and a visco-capillary region, where capillary and/or viscous forces dominate. In the inertial region, an intricate structure of different-scale vortices arises, which is more complicated than film thickness variations there suggest. Conversely, the flow in the visco-capillary region of large-$\textit {Ka} $ fluids is entirely governed by the local free-surface curvature through the action of capillary forces, which impose the pressure distribution in the liquid film. This results in flow separation zones underneath the capillary troughs and a spanwise cellular flow pattern in the region of capillary wave interference. In some cases, capillary waves bridge the large horseshoe humps in the spanwise direction, coupling the two aforementioned regions and leading the flow to oscillate between three- and two-dimensional wave patterns. This persists over long times, as we show by simulations with the low-dimensional model of Scheid et al. (J. Fluid Mech., vol. 562, 2006, pp. 183–222) after satisfactory comparison with our direct simulations at short times. The governing mechanism is connected to the bridging capillary waves, which drain liquid from the horseshoe humps, decreasing their amplitude and wave speed and causing them to retract in the streamwise direction. Overall, it is observed that spanwise flow structures (not accounted for in two-dimensional investigations) are particularly complex due to the absence of gravity in this direction.
9
Cuccia, Nicholas L., Suraj Pothineni, Brady Wu, Joshua Méndez Harper e Justin C. Burton. "Pore-size dependence and slow relaxation of hydrogel friction on smooth surfaces". Proceedings of the National Academy of Sciences 117, n.º 21 (12 de maio de 2020): 11247–56. http://dx.doi.org/10.1073/pnas.1922364117.
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Hydrogels consist of a cross-linked polymer matrix imbibed with a solvent such as water at volume fractions that can exceed 90%. They are important in many scientific and engineering applications due to their tunable physiochemical properties, biocompatibility, and ultralow friction. Their multiphase structure leads to a complex interfacial rheology, yet a detailed, microscopic understanding of hydrogel friction is still emerging. Using a custom-built tribometer, here we identify three distinct regimes of frictional behavior for polyacrylic acid (PAA), polyacrylamide (PAAm), and agarose hydrogel spheres on smooth surfaces. We find that at low velocities, friction is controlled by hydrodynamic flow through the porous hydrogel network and is inversely proportional to the characteristic pore size. At high velocities, a mesoscopic, lubricating liquid film forms between the gel and surface that obeys elastohydrodynamic theory. Between these regimes, the frictional force decreases by an order of magnitude and displays slow relaxation over several minutes. Our results can be interpreted as an interfacial shear thinning of the polymers with an increasing relaxation time due to the confinement of entanglements. This transition can be tuned by varying the solvent salt concentration, solvent viscosity, and sliding geometry at the interface.
10
Aidun, Cyrus K. "Mechanics of a Free-Surface Liquid Film Flow". Journal of Applied Mechanics 54, n.º 4 (1 de dezembro de 1987): 951–54. http://dx.doi.org/10.1115/1.3173144.
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The mechanics of a free surface viscous liquid curtain flowing steadily between two vertical guide wires under the influence of gravity is investigated. The Navier-Stokes equation is integrated over the film thickness and an integro-differential equation is derived for the average film velocity. An approximate nonlinear differential equation, attributed to G. I. Taylor, is obtained by neglecting the higher order terms. An analytical solution is obtained for a similar equation which neglects the surface tension effects and the results are compared with the experimental measurements of Brown (1961).
11
SREENIVAS, K. R., P. K. DE e JAYWANT H. ARAKERI. "Levitation of a drop over a film flow". Journal of Fluid Mechanics 380 (10 de fevereiro de 1999): 297–307. http://dx.doi.org/10.1017/s0022112098003486.
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A vertical jet of water impinging on a horizontal surface produces a radial film flow followed by a circular hydraulic jump. We report a phenomenon where fairly large (1 ml) drops of liquid levitate just upstream of the jump on a thin air layer between the drop and the film flow. We explain the phenomenon using lubrication theory. Bearing action both in the air film and the water film seems to be necessary to support large drops. Horizontal support is given to the drop by the hydraulic jump. A variety of drop shapes is observed depending on the volume of the drop and liquid properties. We show that interaction of the forces due to gravity, surface tension, viscosity and inertia produces these various shapes.
12
Peng, X. F., e G. P. Peterson. "Analysis of Rewetting for Surface Tension Induced Flow". Journal of Heat Transfer 114, n.º 3 (1 de agosto de 1992): 703–7. http://dx.doi.org/10.1115/1.2911337.
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An analytical investigation was conducted to determine the rewetting characteristics of thin, surface tension driven liquid films over heated plates as a function of the fluid properties, the film thickness, and the applied heat flux. Analytical expressions for the maximum sustainable heat flux and the rewetting velocity were developed for both flat and grooved plates and were compared with data from previous investigations. The results indicated good agreement for low film velocities; however, at high velocities the experimental data deviated significantly from the theoretical predictions. It was hypothesized that this deviation was due to the presence of liquid sputtering near the liquid front. To compensate for this liquid sputtering, the expressions for maximum sustainable heat flux and rewetting velocity were modified using an empirical correction factor developed from the data of previous thin film thickness investigations. The resulting modified expressions were found to compare very favorably with available experimental data over a large range of flow conditions and velocities.
13
TSELUIKO, D., M. G. BLYTH, D. T. PAPAGEORGIOU e J. M. VANDEN-BROECK. "Electrified viscous thin film flow over topography". Journal of Fluid Mechanics 597 (1 de fevereiro de 2008): 449–75. http://dx.doi.org/10.1017/s002211200700986x.
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The gravity-driven flow of a liquid film down an inclined wall with periodic indentations in the presence of a normal electric field is investigated. The film is assumed to be a perfect conductor, and the bounding region of air above the film is taken to be a perfect dielectric. In particular, the interaction between the electric field and the topography is examined by predicting the shape of the film surface under steady conditions. A nonlinear, non-local evolution equation for the thickness of the liquid film is derived using a long-wave asymptotic analysis. Steady solutions are computed for flow into a rectangular trench and over a rectangular mound, whose shapes are approximated with smooth functions. The limiting behaviour of the film profile as the steepness of the wall geometry is increased is discussed. Using substantial numerical evidence, it is established that as the topography steepness increases towards rectangular steps, trenches, or mounds, the interfacial slope remains bounded, and the film does not touch the wall. In the absence of an electric field, the film develops a capillary ridge above a downward step and a slight depression in front of an upward step. It is demonstrated how an electric field may be used to completely eliminate the capillary ridge at a downward step. In contrast, imposing an electric field leads to the creation of a free-surface ridge at an upward step. The effect of the electric field on film flow into relatively narrow trenches, over relatively narrow mounds, and down slightly inclined substrates is also considered.
14
Zama, Yoshio, Hiroyasu Eriguchi e Tomohiko Furuhata. "Effect Of Wavy Structure Of Liquid Film On Flow Characteristics Of Impingement Jet Flowing On Fuel Liquid Film". Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (8 de julho de 2024): 1–12. http://dx.doi.org/10.55037/lxlaser.21st.104.
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In recent years, diesel engines have been downsized in order to improve combustion efficiency by using high-pressure injection to atomize the fuel and to increase fuel economy. As a result, the diesel spray flame inevitably impinges on the combustion chamber wall, resulting in heat loss due to heat transfer between the flame and the wall. According to Newton's cooling law, the heat transferred from the flame to the wall is proportional to the heat transfer coefficient, which is closely related to the flow of the spray flame. However, there are few reports on the flow of a spray flame impinging on a wall. The flow characteristics of a non-vaporized spray impinging on a wall surface, assuming that the flow of a spray flame impinging on a wall surface is equivalent to that of a non-vaporized spray. The fuel film formed on the wall affected on the flow characteristics of the spray. When the spray flame impinges on the wall in the engine cylinder, no liquid film is formed on the wall. Still, during cold start, a liquid fuel film may form on the piston wall due to the low temperature in the engine cylinder, resulting in HC and soot emissions. As a result, the spray may flow over the formed film. Therefore, it is necessary to investigate the flow characteristics of the spray flowing over the fuel film. In this study, the experiments using an impingement gas jet were conducted on a wall surface with a fuel film, and the velocity field of the jet after impingement of the wall surface was measured by the time-series PIV. In addition, the thickness of the wavy liquid film formed by the gas jet impingement was measured by using the laser-induced fluorescence (LIF) method, discussing the relationship between the velocity of the jet after wall impingement and the characteristics of the wavy liquid film.
15
Ovcharova, A. S. "Controlling the Free-Surface Profile of Film Flow over Complex Topography". Journal of Applied Mechanics and Technical Physics 45, n.º 4 (julho de 2004): 523–27. http://dx.doi.org/10.1023/b:jamt.0000030329.01002.32.
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Pavlenko, Aleksandr, Anton Surtaev, Oleg Volodin e Vladimir Serdyukov. "The Features Of The Film Flow Of Liquid Nitrogen Over The Corrugated Plates With Combined Microtexture". Siberian Journal of Physics 12, n.º 2 (1 de junho de 2017): 75–84. http://dx.doi.org/10.54362/1818-7919-2017-12-2-75-84.
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Experimental results on hydrodynamics of cryogenic liquid film flow over the surface of the single elements of the structured packing are presented. Based on the comparison of experimental data, the effect of microtexture form, diameter of the holes on the zones of liquid film spreading over a corrugated surface is shown for different values of the film Reynolds number. It is shown that the presence of combined microtexture (with the periodic change in its direction at the height of the sheet) leads to a better spreading of the liquid nitrogen film on the surface of the corrugated perforated sheet. Analysis of experimental data shows that the presence of the periodic zones with vertical orientation of the microchannels on the sheets with the combined microtexture provides the greater flow of liquid through the holes compared to the sheet having the horizontal direction of microtexture. The use of smaller holes, while maintaining the same total area occupied by holes, at the small degree of irrigation also leads to increasing size of the wetting zones on the sheet with combined microtexture.
17
Xue, Danting, Ruigang Zhang, Quansheng Liu e Zhaodong Ding. "Instability of Liquid Film with Odd Viscosity over a Non-Uniformly Heated and Corrugated Substrate". Nanomaterials 13, n.º 19 (28 de setembro de 2023): 2660. http://dx.doi.org/10.3390/nano13192660.
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The effect of odd viscosity on the instability of liquid film along a wavy inclined bottom with linear temperature variation is investigated. By utilizing the long-wave approximation, the non-linear evolution equation of the free surface is derived. By applying the normal mode method, the linear instability of thin film flow is investigated. With the help of multi-scale analysis methods, the weakly non-linear instability of thin film flow is also investigated. The results reveal that the Marangoni effect caused by non-uniform temperature distribution promotes the instability of the liquid film, while the odd viscosity has a stabilizing effect. In addition, for a positive local inclination angle θ, an increase in bottom steepness ζ inhibits the instability of the liquid film flow. In contrast, with a negative local inclination angle θ, increased bottom steepness ζ promotes the instability of the liquid film flow. The results of the temporal linear instability analysis and the weakly non-linear instability analysis have been substantiated through numerical simulations of the non-linear evolution equations.
18
Ozar, B., B. M. Cetegen e A. Faghri. "Experiments on Heat Transfer in a Thin Liquid Film Flowing Over a Rotating Disk". Journal of Heat Transfer 126, n.º 2 (1 de abril de 2004): 184–92. http://dx.doi.org/10.1115/1.1652044.
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An experimental study of heat transfer into a thin liquid film on a rotating heated disk is described. Deionized water was introduced at the center of a heated, horizontal disk with a constant film thickness and uniform radial velocity. Radial distribution of the disk surface temperatures was measured using a thermocouple/slip ring arrangement. Experiments were performed for a range of liquid flow rates between 3.0 lpm and 15.0 lpm. The angular speed of the disk was varied from 0 rpm to 500 rpm. The local heat transfer coefficient was determined based on the heat flux supplied to the disk and the temperature difference between the measured disk surface temperature and the liquid entrance temperature onto the disk. The local heat transfer coefficient was seen to increase with increasing flow rate as well as increasing angular velocity of the disk. Effect of rotation on heat transfer was largest for the lower liquid flow rates with the effect gradually decreasing with increasing liquid flow rates. Semi-empirical correlations are presented in this study for the local and average Nusselt numbers.
19
Fang, Tiegang, Fujun Wang e Bo Gao. "Liquid film flow over an unsteady moving surface with a new stretching velocity". Physics of Fluids 30, n.º 9 (setembro de 2018): 093603. http://dx.doi.org/10.1063/1.5046479.
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Chang, K. H., e L. C. Witte. "Liquid-Solid Contact During Flow Film Boiling of Subcooled Freon-11". Journal of Heat Transfer 112, n.º 2 (1 de maio de 1990): 465–71. http://dx.doi.org/10.1115/1.2910401.
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Liquid-solid contacts were measured for flow film boiling of subcooled Freon-11 over an electrically heated cylinder equipped with a surface microthermocouple probe. No systematic variation of the extent of liquid-solid contact with wall superheat, liquid subcooling, or velocity was detected. Only random small-scale contacts that contribute negligibly to overall heat transfer were detected when the surface was above the homogeneous nucleation temperature of the Freon-11. When large-scale contacts were detected, they led to an unexpected intermediate transition from local film boiling to local transition boiling. An explanation is proposed for these unexpected transitions. A comparison of analytical results that used experimentally determined liquid-solid contact parameters to experimental heat fluxes did not show good agreement. It was concluded that the available model for heat transfer accounting for liquid-solid contact is not adequate for flow film boiling.
21
Mamedov, Asiman, Serhiy Stas e Evhen Lavrukhin. "FEATURES OF THE FILM FLOW OF A LIQUID OVER A VERTICAL SURFACE IN A TRANSVERSE MAGNETIC FIELD". Bulletin of the National Technical University "KhPI". Series: Hydraulic machines and hydraulic units, n.º 2 (24 de janeiro de 2024): 44–48. http://dx.doi.org/10.20998/2411-3441.2023.2.06.
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One of the actual problems of magnetohydrodynamics is the problem of the flow of electrically conductive liquids in thin liquid layers in the presence of a transverse magnetic field. Unfortunately, studies of these problems have not been sufficient so far. The influence of a transverse magnetic field can affect a number of factors: the change in the viscosity of the flow due to the magnetic field on the physico-chemical characteristics of the medium; manifestation of the effect of flow deceleration, which can have a significant effect on the hydrodynamic characteristics of the film flow in the processes of heat and mass transfer. In this regard, in this work was made an attempt to consider the influence of a constant magnetic field on the formation of a thin liquid layer on a vertical surface under the action of ponderomotive forces. As known, ponderomotive forces in the case under consideration can lead to a number of effects associated with a change in viscosity and flow deceleration. To a greater extent, this can manifest itself in thin liquid layers, depending on the ratio of gravitational forces, inertia forces and forces of a magnetic nature. An analysis of the influence of this phenomenon in the considered case of thin liquid layers, as shown in the work, significantly affects the length of the hydrodynamic initial section, the thickness of the liquid layer, and the damping of wave motion in the zone of stabilized flow. Recommendations for calculating these characteristics are presented in this article, in which much attention is paid to the definition of the liquid layer, depending on the ratio between the forces of inertia and the forces of a magnetic nature. An expression was also obtained for determining the distribution of velocities in the zone of a stabilized film flow in a transverse magnetic field. Thus, by comparing the expression for determining the distribution of velocities in a film without the influence of a magnetic field with the expression in the presence of a magnetic field, one can estimate the effect of ponderomotive forces on the flow of a liquid film.
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Chen, Ping-Hei, Min-Sheng Hung e Pei-Pei Ding. "A Transient Method Using Liquid Crystal for Film Cooling Over a Convex surface". International Journal of Rotating Machinery 7, n.º 3 (2001): 153–64. http://dx.doi.org/10.1155/s1023621x01000148.
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In order to explore the effect of blowing ratio on film cooling over a convex surface, the present study adopts the transient liquid crystal thermography for the film cooling measurement on a straight circular hole configuration. The test piece has a strength of curvature(2r/D)of 92.5, pitch to diameter ratio(P/D)of 3 and streamwise injection angle(γ)of35∘All measurements were conducted under the mainstream Reynolds number(Red)of 1700 with turbulence intensity(Tu)of 3.8%, and the density ratio between coolant and mainstream(ρc/ρm)is 0.98. In current study, the effect of blowing ratio(M)on film cooling performance is investigated by varying the range of blowing ratio from 0.5 to 2.0. Two transient tests of different injection flow temperature were conducted to obtain both detailed heat transfer coefficient and film cooling effectiveness distributions of measured region. The present measured results show that both the spanwise averaged heat transfer coefficient and film cooling effectiveness increase with decreased blowing ratio.
23
Woods, David R., e S. P. Lin. "Instability of a liquid film flow over a vibrating inclined plane". Journal of Fluid Mechanics 294 (10 de julho de 1995): 391–407. http://dx.doi.org/10.1017/s0022112095002941.
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The problem of the onset of instability in a liquid layer flowing down a vibrating inclined plane is formulated. For the solution of the problem, the Fourier components of the disturbance are expanded in Chebychev polynomials with time-dependent coefficients. The reduced system of ordinary differential equations is analysed with the aid of Floquet theory. The interaction of the long gravity waves, the relatively short shear waves and the parametrically resonated Faraday waves occurring in the film flow is studied. Numerical results show that the long gravity waves can be significantly suppressed, but cannot be completely eliminated by use of the externally imposed oscillation on the incline. At small angles of inclination, the short shear waves may be exploited to enhance the Faraday waves. For a given set of relevant flow parameters, there exists a critical amplitude of the plane vibration below which the Faraday wave cannot be generated. At a given amplitude above this critical one, there also exists a cutoff wavenumber above which the Faraday wave cannot be excited. In general the critical amplitude increases, but the cutoff wavenumber decreases, with increasing viscosity. The cutoff wavenumber also decreases with increasing surface tension. The application of the theory to a novel method of film atomization is discussed.
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Rezk, Amgad R., Ofer Manor, Leslie Y. Yeo e James R. Friend. "Double flow reversal in thin liquid films driven by megahertz-order surface vibration". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, n.º 2169 (8 de setembro de 2014): 20130765. http://dx.doi.org/10.1098/rspa.2013.0765.
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Arising from an interplay between capillary, acoustic and intermolecular forces, surface acoustic waves (SAWs) are observed to drive a unique and curious double flow reversal in the spreading of thin films. With a thickness at or less than the submicrometre viscous penetration depth, the film is seen to advance along the SAW propagation direction, and self-similarly over time t 1/4 in the inertial limit. At intermediate film thicknesses, beyond one-fourth the sound wavelength λ ℓ in the liquid, the spreading direction reverses, and the film propagates against the direction of the SAW propagation. The film reverses yet again, once its depth is further increased beyond one SAW wavelength. An unstable thickness region, between λ ℓ /8 and λ ℓ /4, exists from which regions of the film either rapidly grow in thickness to exceed λ ℓ /4 and move against the SAW propagation, consistent with the intermediate thickness films, whereas other regions decrease in thickness below λ ℓ /8 to conserve mass and move along the SAW propagation direction, consistent with the thin submicrometre films.
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Pavlenko, Ivan, Oleksandr Liaposhchenko, Marek Ochowiak, Radosław Olszewski, Maryna Demianenko, Oleksandr Starynskyi, Vitalii Ivanov, Vitalii Yanovych, Sylwia Włodarczak e Michał Doligalski. "Three-Dimensional Mathematical Model of the Liquid Film Downflow on a Vertical Surface". Energies 13, n.º 8 (15 de abril de 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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Ruschak, Kenneth J., e Steven J. Weinstein. "Thin-Film Flow at Moderate Reynolds Number". Journal of Fluids Engineering 122, n.º 4 (5 de julho de 2000): 774–78. http://dx.doi.org/10.1115/1.1319499.
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Viscous, laminar, gravitationally-driven flow of a thin film over a round-crested weir is analyzed for moderate Reynolds numbers. A previous analysis of this flow utilized a momentum integral approach with a semiparabolic velocity profile to obtain an equation for the film thickness (Ruschak, K. J., and Weinstein, S. J., 1999, “Viscous Thin-Film Flow Over a Round-Crested Weir,” ASME J. Fluids Eng., 121, pp. 673–677). In this work, a viscous boundary layer is introduced in the manner of Haugen (Haugen, R., 1968, “Laminar Flow Around a Vertical Wall,” ASME J. Appl. Mech. 35, pp. 631–633). As in the previous analysis of Ruschak and Weinstein, the approximate equations have a critical point that provides an internal boundary condition for a bounded solution. The complication of a boundary layer is found to have little effect on the thickness profile while introducing a weak singularity at its beginning. The thickness of the boundary layer grows rapidly, and there is little cumulative effect of the increased wall friction. Regardless of whether a boundary layer is incorporated, the approximate free-surface profiles are close to profiles from finite-element solutions of the Navier-Stokes equation. Similar results are obtained for the related problem of developing flow on a vertical wall (Cerro, R. L., and Whitaker, S., 1971, “Entrance Region Flows With a Free Surface: the Falling Liquid Film,” Chem. Eng. Sci., 26, pp. 785–798). Less accurate results are obtained for decelerating flow on a horizontal wall (Watson, E. J., 1964, “The Radial Spread of a Liquid Jet Over a Horizontal Plane,” J. Fluid Mech. 20, pp. 481–499) where the flow is not gravitationally driven. [S0098-2202(00)01904-0]
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Xu, Hang, Ioan Pop e Xiang-Cheng You. "Flow and heat transfer in a nano-liquid film over an unsteady stretching surface". International Journal of Heat and Mass Transfer 60 (maio de 2013): 646–52. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2013.01.046.
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Reisfeld, B., e S. G. Bankoff. "Non-isothermal flow of a liquid film on a horizontal cylinder". Journal of Fluid Mechanics 236 (março de 1992): 167–96. http://dx.doi.org/10.1017/s0022112092001381.
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We consider the flow of a viscous liquid film on the surface of a cylinder that is heated or cooled. Lubrication theory is used to study a thin film under the influence of gravity, capillary, thermocapillary, and intermolecular forces. We derive evolution equations for the interface shapes as a function of the azimuthal angle about the cylinder that govern the behaviour of the film subject to the above coupled forces. We use both analytical and numerical techniques to elucidate the dynamics and steady states of the thin layer over a wide range of thermal conditions and material properties. Finally, we extend our derivation to the case of three-dimensional dynamics and explore the stability of the film to small axial disturbances.
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Shahzad, Azeem, Uzma Gulistan, Ramzan Ali, Azhar Iqbal, Ali Cemal Benim, Muhammad Kamran, Salah Ud-Din Khan, Shahab Ud-Din Khan e Aamir Farooq. "Numerical Study of Axisymmetric Flow and Heat Transfer in a Liquid Film over an Unsteady Radially Stretching Surface". Mathematical Problems in Engineering 2020 (28 de agosto de 2020): 1–9. http://dx.doi.org/10.1155/2020/6737243.
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The main emphasis on this paper is to analyze the axisymmetric flow and heat transfer in a liquid film over an unsteady radially stretching surface in the presence of a transverse magnetic field. The similarity transformations are used to reduce the highly nonlinear governing partial differential equations for momentum and energy into a set of ordinary differential equations. A numerical scheme is developed for the reduced nonlinear differential equations for the velocity and temperature fields. The literature survey shows that the present problem of thin film flow over a radially stretching sheet has not been studied before. The features of the flow and heat transfer characteristic for different values of governing parameters such as unsteadiness parameter, Prandtl number, Eckert number, and magnetic parameter are thoroughly examined. This study noticed that, by increasing the magnetic parameter and unsteadiness parameter, film thickness decreases.
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Sakhnov, A., O. A. Volodin, N. I. Pecherkin e A. N. Pavlenko. "Numerical Modelling of Liquid Film Spreading Dynamics over Smooth Vertical Surface under Isothermal Conditions". Journal of Physics: Conference Series 2119, n.º 1 (1 de dezembro de 2021): 012054. http://dx.doi.org/10.1088/1742-6596/2119/1/012054.
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Abstract The paper presents numerical modelling of the liquid film spreading dynamics of the R21 (mol. fraction: 0.9) and R114 refrigerants mixture. We considered an outer flow along a round vertical cylinder at Reynolds number of 104 and various contact angles. The simulation was performed in OpenFOAM software on the basis of the volume of fluid (VOF) method. We have shown that the wetting front deforms at wetting angles of 30 and 50 degrees, and regular jets form. At the same time, it was demonstrated that at the wetting angle of 10 degrees the spreading front has practically a flat shape, but one may see some regular thickenings of the liquid film along the contact line of the front.
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Ilie, Marius Ciprian, Ioana Maior, Cristian Eugen Raducanu, Iuliana Mihaela Deleanu, Tanase Dobre e Oana Cristina Parvulescu. "Experimental Investigation and Modeling of Film Flow Corrosion". Metals 13, n.º 8 (9 de agosto de 2023): 1425. http://dx.doi.org/10.3390/met13081425.
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The paper focuses on the experimental investigation and mathematical modeling of the corrosion of steel when a film of water flows over its surface. The experimental monitoring of corrosion dynamics in the flowing film was carried out using a laboratory pilot model, exploited in such a way as to obtain data necessary to identify some characteristic parameters of the mathematical model of this problem. The mathematical model of the case takes into account the transfer of oxygen through the liquid film flowing on the surface of the corroding plate where the chemical surface processes characteristic of corrosion occur (dissolution of Fe, oxidation of Fe2+ to Fe3+, formation of surface deposit, etc.). Experimental measurements were used to identify the parameters of the mathematical model, especially the reaction constant of the Fe dissolution rate and the surface oxidation yield of Fe2+ to Fe3+. Calculation of the correlation coefficients for the apparent constant surface reaction rate and process factors showed that they correlate strongly and non-linearly with the Reynolds number (Re) of the film flow, with the cumulative flow duration, and with the cumulative standby time of the experiments. Using the dynamics of the resistance to the transfer of oxygen through the rust film and the dynamics of its thickness resulting from the specific flow of rust deposition, the apparent oxygen diffusion coefficient through the rust film formed on the plate was expressed.
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Liu, Xiao Bo, Jian Run Zhang, Pu Li e Xin Hua Wang. "Analysis and Calculation of Vacuum Film Deaeration for High Viscosity Liquids". Applied Mechanics and Materials 141 (novembro de 2011): 76–82. http://dx.doi.org/10.4028/www.scientific.net/amm.141.76.
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A theoretical analysis of Vacuum Film Deaeration(VFD) based on the characteristics of fluid film on a rotating cone surface is carried out. The motion equation of bubble is derived to find out its relative slip velocity in the flowing film. And the bubbles removal time from the high viscosity liquid is discussed. The thickness model of liquid film on the rotating surface and the residence time of the film flows over the surface are built in this paper. It is found that the thickness and the velocity of the flowing film on the rotating cone surface are the key parameters for VFD; the time of bubble remove mainly includes the growth time and the rest time; the velocity of bubble is slightly lagging behind the main flow; the low angular velocity has little effect on the film thickness; and the time of VFD for flowing film is less than that of static film.
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Khan, Abdul Samad, Yufeng Nie e Zahir Shah. "Impact of Thermal Radiation on Magnetohydrodynamic Unsteady Thin Film Flow of Sisko Fluid over a Stretching Surface". Processes 7, n.º 6 (12 de junho de 2019): 369. http://dx.doi.org/10.3390/pr7060369.
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The current article discussed the heat transfer and thermal radioactive of the thin liquid flow of Sisko fluid on unsteady stretching sheet with constant magnetic field (MHD). Here the thin liquid fluid flow is assumed in two dimensions. The governing time-dependent equations of Sisko fluid are modeled and reduced to Ordinary differential equations (ODEs) by use of Similarity transformation with unsteadiness non-dimensionless parameter S t . To solve the model problem, we used analytical and numerical techniques. The convergence of the problem has been shown numerically and graphically using Homotopy Analysis Method (HAM). The obtained numerical result shows that the HAM estimates of the structures is closed with this result. The Comparison of these two methods (HAM and numerical) has been shown graphically and numerically. The impact of the thermal radiation R d and unsteadiness parameter S t over thin liquid flow is discovered analytically. Moreover, to know the physical representation of the embedded parameters, like β , magnetic parameter M, stretching parameter ξ , and Sisko fluid parameters ε have been plotted graphically and discussed.
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Brož, Zdeněk, e Mirko Endršt. "The effect of surface active agents on the mass transfer coefficient in vertical film flow of liquid over the surface of expanded metal sheet packing". Collection of Czechoslovak Chemical Communications 51, n.º 2 (1986): 302–13. http://dx.doi.org/10.1135/cccc19860302.
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Experimental data have been used on absorption of poorly soluble gases, helium, carbon dioxide, and propane, to study the mechanism of interfacial mass transfer in vertical gravitational film flow down the surface of the expanded metal sheet. It has been found that upon addition of surface active agents into water, the original almost freely moving liquid-gas interfacial surface behaves similarly as a liquid-solid surface. Two adjustable hydrodynamic parameters have been evaluated on the basis of the film penetration theory with the physical meaning of the dimensionless thickness of an unmixed region near the interface ϑ+ = 0.4 and the characteristic length < scale of the disturbance λ+ = 26.4.
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Suzzi, Nicola, e Giulio Croce. "Numerical Bifurcation Analysis of a Film Flowing over a Patterned Surface through Enhanced Lubrication Theory". Fluids 6, n.º 11 (9 de novembro de 2021): 405. http://dx.doi.org/10.3390/fluids6110405.
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The bifurcation analysis of a film falling down an hybrid surface is conducted via the numerical solution of the governing lubrication equation. Instability phenomena, that lead to film breakage and growth of fingers, are induced by multiple contamination spots. Contact angles up to 75∘ are investigated due to the full implementation of the free surface curvature, which replaces the small slope approximation, accurate for film slope lower than 30∘. The dynamic contact angle is first verified with the Hoffman–Voinov–Tanner law in case of a stable film down an inclined plate with uniform surface wettability. Then, contamination spots, characterized by an increased value of the static contact angle, are considered in order to induce film instability and several parametric computations are run, with different film patterns observed. The effects of the flow characteristics and of the hybrid pattern geometry are investigated and the corresponding bifurcation diagram with the number of observed rivulets is built. The long term evolution of induced film instabilities shows a complex behavior: different flow regimes can be observed at the same flow characteristics under slightly different hybrid configurations. This suggest the possibility of controlling the rivulet/film transition via a proper design of the surfaces, thus opening the way for relevant practical application.
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Mimouni, S., N. Mechitoua, A. Foissac, M. Hassanaly e M. Ouraou. "CFD Modeling of Wall Steam Condensation: Two-Phase Flow Approach versus Homogeneous Flow Approach". Science and Technology of Nuclear Installations 2011 (2011): 1–10. http://dx.doi.org/10.1155/2011/941239.
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The present work is focused on the condensation heat transfer that plays a dominant role in many accident scenarios postulated to occur in the containment of nuclear reactors. The study compares a general multiphase approach implemented in NEPTUNE_CFD with a homogeneous model, of widespread use for engineering studies, implemented inCode_Saturne. The model implemented in NEPTUNE_CFD assumes that liquid droplets form along the wall within nucleation sites. Vapor condensation on droplets makes them grow. Once the droplet diameter reaches a critical value, gravitational forces compensate surface tension force and then droplets slide over the wall and form a liquid film. This approach allows taking into account simultaneously the mechanical drift between the droplet and the gas, the heat and mass transfer on droplets in the core of the flow and the condensation/evaporation phenomena on the walls. As concern the homogeneous approach, the motion of the liquid film due to the gravitational forces is neglected, as well as the volume occupied by the liquid. Both condensation models and compressible procedures are validated and compared to experimental data provided by the TOSQAN ISP47 experiment (IRSN Saclay). Computational results compare favorably with experimental data, particularly for the Helium and steam volume fractions.
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Harper, J. F. "The leading edge of an oil slick, soap film, or bubble stagnant cap in Stokes flow". Journal of Fluid Mechanics 237 (abril de 1992): 23–32. http://dx.doi.org/10.1017/s0022112092003331.
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Trace impurities often collect on the upstream side of an obstacle in the surface of flowing liquid. The transition from practically free surface to surface sufficiently clogged to be treated as stationary can be quite sharp. The viscous flow underneath is nonlinearly coupled to the convective mass transfer of surface-active material. For two-dimensional flow at high Reynolds number the first observations were due to Thoreau, Langton and Reynolds over 100 years ago, and the theory was given by Harper & Dixon in 1974. If the whole problem is considered from a frame of reference moving with the stream instead of fixed to the downstream surface film, the solution refers to the leading edge of a slowly spreading oil slick.The present work gives the theory corresponding to Harper & Dixon's for low Reynolds numbers (Stokes flow), for which there is a very simple leading approximation near the transition for a soluble surfactant, and a more complicated one, which can still be found exactly, for an insoluble surfactant which spreads onto clear liquid by surface diffusion. In both cases the surface remains flat: the ridge often observed is not a Stokes flow phenomenon.The results are used to clarify the circumstances in which Savic's stagnant-cap approximation is useful for a bubble rising in a viscous liquid: the rear stagnation point now plays the role of the obstacle in the surface, and the flow near the surface transition can be treated locally as if it were two-dimensional instead of axisymmetric.
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Polajnar, M., B. Bizjan, B. Širok e M. Kalin. "High-speed optical imaging of liquid film flow and liquid macro-slip over free surfaces with different surface energies". Lubrication Science 29, n.º 8 (21 de maio de 2017): 557–66. http://dx.doi.org/10.1002/ls.1388.
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Jawad, Muhammad, Zahir Shah, Saeed Islam, Waris Khan e Aurang Zeb Khan. "Nanofluid thin film flow of Sisko fluid and variable heat transfer over an unsteady stretching surface with external magnetic field". Journal of Algorithms & Computational Technology 13 (janeiro de 2019): 174830181983245. http://dx.doi.org/10.1177/1748301819832456.
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This research paper investigates two dimensional liquid film flow of Sisko nanofluid with variable heat transmission over an unsteady stretching sheet in the existence of uniform magnetic field. The basic governing time-dependent equations of the nanofluid flow phenomena with Sisko fluid are modeled and reduced to a system of differential equations with use of similarity transformation. The significant influence of Brownian motion and thermophoresis has been taken in the nanofluids model. An optimal approach is used to obtain the solution of the modeled problems. The convergence of the Homotopy Analysis Method (HAM) method has been shown numerically. The variation of the skin friction, Nusselt number and Sherwood number, their influence on liquid film flow with heat and mass transfer have been examined. The influence of the unsteadiness parameter [Formula: see text] over thin film is explored analytically for different values. Moreover for comprehension, the physical presentation of the embedded parameters, like [Formula: see text], magnetic parameter [Formula: see text], stretching parameter [Formula: see text] and Sisko fluid parameters [Formula: see text], Prandtl number Pr, thermophoretic parameter [Formula: see text], Brownian motion parameter [Formula: see text], Schmidt number [Formula: see text] have been represented by graph and discussed.
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Khan, Waris, Muhammad Idress, Taza Gul, Muhammad Altaf Khan e Ebenezer Bonyah. "Three non-Newtonian fluids flow considering thin film over an unsteady stretching surface with variable fluid properties". Advances in Mechanical Engineering 10, n.º 10 (outubro de 2018): 168781401880736. http://dx.doi.org/10.1177/1687814018807361.
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This research examines the features of liquid film of non-Newtonian fluids under the influence of thermophoresis. For this study, we proposed a mathematical model for Jeffrey, Maxwell, and Oldroyd-B fluids and concluded the unsteady stretched surface in the existence of a magnetic field and also the thermal conductivity was measured which is directly related to the temperature whereas the viscosity inversely related to the temperature. Inserting the thermophoretic effect which improved the thermal conductivity of Jeffrey fluid over the Oldroyd-B and Maxwell fluids. The model is helpful for the liquid flow of Jeffrey, Maxwell, and Oldroyd-B fluid including the Brownian motion parameter effect. The results have been obtained through optimal approach compared with numerical (ND-Solve) method. Study mainly focused to understand the physical appearance of the embedded parameters based on the characteristic length of the liquid flow. The behavior of skin friction, local Nusselt number, and Sherwood number has been described numerically for the dynamic constraints of the problem. The obtained results are drafted graphically and discussed.
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Suzzi, Nicola, e Giulio Croce. "Numerical simulation of shear driven film instability over heterogeneous surfaces via enhanced lubrication theory". Journal of Physics: Conference Series 2685, n.º 1 (1 de janeiro de 2024): 012019. http://dx.doi.org/10.1088/1742-6596/2685/1/012019.
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Abstract The prediction of the transition between continuous film, ensemble of rivulets and moving droplets is crucial in applications such as in-flight icing on airfoil wings or a number of chemical reactors. Here, lubrication theory is used to numerically investigate the stability of a continuous liquid film, driven by shear, over a heterogeneous surface. The disjoining pressure is used to model surface wettability, while the full implementation of the film curvature allows to investigate contact angles up to 60°. Different heterogeneous surface configurations occurring in real problems are investigated. An extended computational campaign records the transition from continuous film to rivulet regime and, if present, the further transition from rivulet to droplets at different flow conditions. A moving grid approach allows for accurate prediction of instability phenomena at low computational cost. The numerical results are successfully validated with experimental evidence in case of critical flow rate leading to a stable dry patch and compared with literature results involving the inherently multiscale in-flight icing phenomenon, providing useful statistical information, required to transfer the present detailed small-scale information into larger scale CFD computational approaches.
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Tripathi, R. "Marangoni convection in the transient flow of hybrid nanoliquid thin film over a radially stretching disk". Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 235, n.º 4 (12 de abril de 2021): 800–811. http://dx.doi.org/10.1177/09544089211008052.
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Within a magnetohydrodynamic environment, Marangoni convection (Thermocapilarity effect) in an unsteady thin film of hybrid nanoliquid flow over a disk has been discussed. A set of simplified Navier-Stokes equation using boundary layer theory is written in order to model the above mentioned flow situation. The dissipative effects caused by viscosity and magnetic field have been incorporated in temperature-balance equation. A suitable choice of transform variables facilitate a system of ordinary differential equations (ODEs) from original partial differential equations (PDEs) representing the flow phenomena. This system of ODEs are solved by shooting technique in conjunction with Runge-Kutta 4th order numerical scheme. This study reveals that by increasing the surface tension along the liquid-air interface, the velocity of hybrid nanoliquid can be increased. In the context of this research work, the hybrid nanoliquid prepared by dispersing blade shaped [Formula: see text] and Cu nanoparticles, is an ideal liquid as far as liquid coolants are concerned.
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Osiptsov, A. N., e E. G. Shapiro. "Two-phase flow over a surface with the formation of a liquid film by particle deposition". Fluid Dynamics 24, n.º 4 (1990): 559–66. http://dx.doi.org/10.1007/bf01052417.
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Sailaja, M., R. Hemadri Reddy, R. Saravana e K. Avinash. "Aligned magnetic field effect on unsteady liquid film flow of Casson fluid over a stretching surface". IOP Conference Series: Materials Science and Engineering 263 (novembro de 2017): 062008. http://dx.doi.org/10.1088/1757-899x/263/6/062008.
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Basu, S., e B. M. Cetegen. "Effect of Hydraulic Jump on Hydrodynamics and Heat Transfer in a Thin Liquid Film Flowing Over a Rotating Disk Analyzed by Integral Method". Journal of Heat Transfer 129, n.º 5 (26 de junho de 2006): 657–63. http://dx.doi.org/10.1115/1.2712854.
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Flow and heat transfer in a liquid film flowing over the surface of a rotating disk was analyzed by integral technique. The integral analysis includes the prediction of the hydraulic jump and its effects on heat transfer. The results of this analysis are compared to the earlier results that did not include this effect. At low inlet Reynolds numbers and high Rossby numbers, corresponding to low film inertia and low rotation rates, respectively, a hydraulic jump appears on the disk surface. The location of the jump and the liquid film height at this location are predicted. A scaling analysis of the equations governing the film thickness provided a semi-empirical expression for these quantities that was found to be in very good agreement with numerical results. Heat transfer analysis shows that the Nusselt numbers for both constant disk surface temperature and constant disk surface heat flux boundary conditions are lowered in the vicinity of the hydraulic jump due to the thickened liquid film. This effect can be more pronounced for the constant heat flux case depending on the location of the hydraulic jump. The Nusselt number exhibits a turning point at the jump location and can have higher values downstream of the hydraulic jump compared to those obtained from the analysis that does not include the gravitational effects.
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Sun, Chunhua, Zhi Ning, Xinqi Qiao, Ming Lv, Juan Fu, Jin Zhao e Xintao Wang. "Numerical simulation of gas–liquid flow behavior in the nozzle exit region of an effervescent atomizer". International Journal of Spray and Combustion Dynamics 11 (janeiro de 2019): 175682771882159. http://dx.doi.org/10.1177/1756827718821592.
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The pressure drop and particular geometric structure of the nozzle exit region of an effervescent atomizer cause complex changes in the flow pattern, which could affect the spray performance. In this study, the gas–liquid two-phase flow behavior in the nozzle exit region of the effervescent atomizer was investigated numerically. The results show that the flow behaviors in the nozzle exit region have disparate characteristics with different upstream flow regimes. For upstream churn flow, the liquid film morphology is closely related to fluctuation in the gas–liquid velocity, and the flow parameters (fluids’ velocities and gas void fraction) at the exit section vary regularly with time. For upstream bubbly flow, the instantaneous gas void fraction is determined by the bubble distribution inside the mixing chamber. The bubble will form a tadpole-like shape as a result of the complex flow field and the surface tension. The flow parameters at the exit section are in an oscillatory decay, and the fluctuation amplitude is larger than for churn flow. For upstream slug flow, the gas void fraction varies significantly with time. The discrete characteristic of the gas–liquid flow parameters at exit section is very obvious.
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Pascall, Andrew J., e Todd M. Squires. "Electrokinetics at liquid/liquid interfaces". Journal of Fluid Mechanics 684 (28 de setembro de 2011): 163–91. http://dx.doi.org/10.1017/jfm.2011.288.
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AbstractElectrokinetic effects at liquid/liquid interfaces have received considerably less attention than at solid/liquid interfaces. Because liquid/liquid interfaces are generally mobile, one might expect electrokinetic effects over a liquid/liquid interface to be faster than over an equivalent solid surface. The earliest predictions for the electrophoretic mobility of charged mercury drops – distinct approaches by Frumkin, along with Levich, and Booth – differed by $O(a/ {\lambda }_{D} )$, where $a$ is the radius of the drop and ${\lambda }_{D} $ is the Debye length. Seeking to reconcile this rather striking discrepancy, Levine & O’Brien showed double-layer polarization to be the key ingredient. Without a physical mechanism by which electrokinetic effects are enhanced, however, it is difficult to know how general the enhancement is – whether it holds only for liquid metal surfaces, or more generally, for all liquid/liquid surfaces. By considering a series of systems in which a planar metal strip is coated with either a liquid metal or liquid dielectric, we show that the central physical mechanism behind the enhancement predicted by Frumkin is the presence of an unmatched electrical stress upon the electrolyte/liquid interface, which establishes a Marangoni stress on the droplet surface and drives it into motion. The source of the unbalanced electrokinetic stress on a liquid metal surface is clear – metals represent equipotential surfaces, so no field exists to drive an equal and opposite force on the surface charge. This might suggest that liquid metals represent a unique system, since dielectric liquids can support finite electric fields, which might be expected to exert an electrical stress on the surface charge that balances the electric stress. We demonstrate, however, that electrical and osmotic stresses on relaxed double layers internal to dielectric liquids precisely cancel, so that internal electrokinetic stresses generally vanish in closed, ideally polarizable liquids. The enhancement predicted by Frumkin for liquid mercury drops can thus be expected quite generally over ideally polarizable liquid drops. We then reconsider the electrophoretic mobility of spherical drops, and reconcile the approaches of Frumkin and Booth: Booth’s neglect of double-layer polarization leads to a standard electro-osmotic flow, without the enhancement, and Frumkin’s neglect of the detailed double-layer dynamics leads to the enhanced electrocapillary motion, but does not capture the (sub-dominant) electrophoretic motion. Finally, we show that, while the electrokinetic flow over electrodes coated with thin liquid films is $O(d/ {\lambda }_{D} )$ faster than over solid/liquid interfaces, the Dukhin number, $\mathit{Du}$, which reflects the importance of surface conduction to bulk conduction, generally increases by a smaller amount [$O(d/ L)$], where $d$ is the thickness of film and $L$ is the length of the electrode. This suggests that liquid/liquid interfaces may be utilized to enhance electrokinetic velocities in microfluidic devices, while delaying the onset of high-$\mathit{Du}$ electrokinetic suppression.
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Guo, S. M., C. C. Lai, T. V. Jones, M. L. G. Oldfield, G. D. Lock e A. J. Rawlinson. "Influence of Surface Roughness on Heat Transfer and Effectiveness for a Fully Film Cooled Nozzle Guide Vane Measured by Wide Band Liquid Crystals and Direct Heat Flux Gages". Journal of Turbomachinery 122, n.º 4 (1 de fevereiro de 2000): 709–16. http://dx.doi.org/10.1115/1.1312798.
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The influence of surface roughness on heat transfer coefficient and cooling effectiveness for a fully film cooled three-dimensional nozzle guide vane (NGV) has been measured in a transonic annular cascade using wide band liquid crystal and direct heat flux gages (DHFGs). The liquid crystal methods were used for rough surface measurements and the DHFGs were used for the smooth surfaces. The measurements have been made at engine representative Mach and Reynolds numbers and inlet free-stream turbulence intensity. The aerodynamic and thermodynamic characteristics of the coolant flow have been modeled to represent engine conditions by using a heavy “foreign gas” (30.2 percent SF6 and 69.8 percent Ar by weight). Two cooling geometries (cylindrical and fan-shaped holes) have been tested. The strategies of obtaining accurate heat transfer data using a variety of transient heat transfer measurement techniques under the extreme conditions of transonic flow and high heat transfer coefficient are presented. The surfaces of interest are coated with wide-band thermochromic liquid crystals, which cover the range of NGV surface temperature variation encountered in the test. The liquid crystal has a natural peak-to-peak roughness height of 25 μm creating a transitionally rough surface on the NGV. The time variation of color is processed to give distributions of both heat transfer coefficient and film cooling effectiveness over the NGV surface. The NGV was first instrumented with the DHFGs and smooth surface tests preformed. Subsequently the surface was coated with liquid crystals for the rough surface tests. The DHFGs were then employed as the means of calibrating the liquid crystal layer. The roughness of 25 μm, which is the typical order of roughness for the in-service turbine blades and vanes, increases the heat transfer coefficient by up to 50 percent over the smooth surface level. The film cooling effectiveness is influenced less by the roughness. [S0889-504X(00)00804-7]
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Shmeliova, Dina V., Sergey V. Pasechnik, Semen S. Kharlamov, Alexander V. Dubtsov, Alexandre V. Zakharov, Sarah Loebner e Svetlana Santer. "Photo-Induced Relief in Rheology of Liquid Crystals". Symmetry 15, n.º 3 (14 de março de 2023): 722. http://dx.doi.org/10.3390/sym15030722.
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In this paper, we report the first experimental results on capillary shear flows of a nematic liquid crystal 5CB (4-cyano-4′-pentylbiphenyl), arising due to interaction of the anisotropic liquid, correspondent to the continuous rotational symmetry, with photo-profiled polymer surfaces. The regular surface relief was obtained due to opto-mechanical deformation of azobenzene containing potoresponsive polymer film (PAZO) during irradiation with two-beam interference. Such surface treatment makes it possible to obtain a regular submicron profile with well-defined characteristics (direction, period, and height). The polarizing microscopy (PM) and dynamic light scattering (DLS) techniques were used to determine the direction of the surface orientation of LC and anchoring strength, which characterize the interaction of LC with the photo-profiled polymer surface. Two types of shear flows—spreading of LC droplets and capillary flow in a plane capillary, induced by the interaction of LC with one or two photo-profiled surfaces—were investigated for different directions of the flow relative to the direction of the relief. Strong anisotropy in the dynamics of the precursor film and contact line motion, as well as in the dynamical contact angle, was established. The experimental results were analyzed and compared with those previously obtained at the investigation of the spreading of LC droplets over a mechanically stamped submicron profile and capillary flows in plane capillaries with photo-aligned surfaces.
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Panda, Satyananda, Mathieu Sellier, M. C. S. Fernando e M. K. Abeyratne. "Process Parameter Identification in Thin Film Flows Driven by a Stretching Surface". International Journal of Engineering Mathematics 2014 (21 de julho de 2014): 1–12. http://dx.doi.org/10.1155/2014/485431.
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The flow of a thin liquid film over a heated stretching surface is considered in this study. Due to a potential nonuniform temperature distribution on the stretching sheet, a temperature gradient occurs in the fluid which produces surface tension gradient at the free surface of the thin film. As a result, the free surface deforms and these deformations are advected by the flow in the stretching direction. This work focuses on the inverse problem of reconstructing the sheet temperature distribution and the sheet stretch rate from observed free surface variations. This work builds on the analysis of Santra and Dandapat (2009) who, based on the long-wave expansion of the Navier-Stokes equations, formulate a partial differential equation which describes the evolution of the thickness of a film over a nonisothermal stretched surface. In this work, we show that after algebraic manipulation of a discrete form of the governing equations, it is possible to reconstruct either the unknown temperature field on the sheet and hence the resulting heat transfer or the stretching rate of the underlying surface. We illustrate the proposed methodology and test its applicability on a range of test problems.