Showing papers on "Marangoni effect published in 2007"
TL;DR: It is demonstrated that the Marangoni flow can significantly influence the resulting patterns of particle deposition in the face of nonuniform evaporation.
Abstract: Nonuniform evaporation from sessile droplets induces radial convection within the drop, which produces the well-known ‘‘coffee-ring’’ effect. The evaporation also induces a gradient in temperature and consequently a gradient in surface tension, generating a Marangoni flow. Here we investigate theoretically and experimentally the thermal Marangoni flow and establish criteria to gauge its influence. An asymptotic analysis indicates that the direction of the flow depends on the relative thermal � ;
526 citations
TL;DR: In this article, the existence of the Marangoni effect in pure water droplets has been observed by using fluorescent nanoparticles, which indicate that a stagnation point where the surface flow, the surface tension gradient, and the surface temperature gradient change their directions exists at the droplet surface.
Abstract: Marangoni effect has been observed in many liquids, but its existence in pure water is still a debated problem. In the present work, the Marangoni flow in evaporating water droplets has been observed by using fluorescent nanoparticles. Flow patterns indicate that a stagnation point where the surface flow, the surface tension gradient, and the surface temperature gradient change their directions exists at the droplet surface. The deduced nonmonotonic variation of the droplet surface temperature, which is different from that in some previous works, is explained by a heat transfer model considering the adsorbed thin film of the evaporating liquid droplet.
246 citations
TL;DR: In this article, the flux effect on TIG weld shape variations is investigated by application of the heat transfer and fluid flow model, and the simulation makes use of Nimonic 263 alloy, TiO,TiO2 and Ti2O3 as the flux.
117 citations
TL;DR: In this paper, the flow of a locally heated liquid film moving under the friction of gas in a channel is considered through theoretical and numerical modeling and conducting experiments, and the critical heat flux at which an initial stable dry patch forms for a shear-driven liquid film can be several times higher than that for a vertical falling liquid film, making shear driven liquid films more suitable for cooling applications.
105 citations
TL;DR: In this article, the effect of Marangoni convection on the flow and heat transfer within a power-law liquid film on an unsteady stretching sheet is examined, and the governing equations are non-dimensionalized using suitable transformation variables and the resulting transformed PDEs are then solved numerically by an implicit finite-difference scheme.
103 citations
TL;DR: It is found that thermophoresis due to surface forces is insensitive to hydrodynamic interactions, and the thermal diffusion coefficient D(T) of polymer solutions is independent of molecular weight and concentration.
Abstract: In a hydrodynamic approach to thermophoretic transport in colloidal suspensions, the solute velocity u and the solvent flow v(r) are derived from Stokes' equation, with slip boundary conditions imposed by thermal Marangoni forces. The resulting fluid velocity field v(r) significantly differs from that induced by an externally driven particle. We find, in particular, that thermophoresis due to surface forces is insensitive to hydrodynamic interactions. As a consequence, the thermal diffusion coefficient D(T) of polymer solutions is independent of molecular weight and concentration.
99 citations
TL;DR: An experimental study of transient drop rise velocities and mass transfer rates was carried out in the system toluene/acetone/water which is known to show interfacial instabilities as mentioned in this paper.
92 citations
TL;DR: In this article, the authors studied the drying process of polymer solution drops put on a wettable substrate and showed that the morphology is not determined by the evaporation process, the "coffee stain" effect, but essentially by the capillary instabilities.
Abstract: We studied the drying process of polymer solution drops put on a wettable substrate. Three stages can be identified. First, the droplet spreads until a maximum radius where evaporation becomes dominant. The second phase is characterized by a constant radius due to competition between spreading and evaporation of the solvent. Finally, the contact line recedes until complete evaporation of the solvent. We show that, for complex fluids (highly viscous polymer), the morphology is not determined by the evaporation process, the "coffee stain" effect but essentially by the capillary instabilities. Using the appropriate couple of polymer/solvent, we were able to obtain a outward, inward or a lack of Marangoni flow in the droplets, leading to the formation of a rim, a drop or a uniform film, respectively.
88 citations
TL;DR: In this paper, the role of Marangoni effects in heat pipes with aqueous solutions of long-chain alcohols, proposed to replace common pure liquids used in conventional heat pipes.
76 citations
TL;DR: It is shown that the flow field of the evaporating liquid is strongly affected by the presence of the thermocapillary convection, and when the results obtained from both water and organic liquids are compared, they give further insight into the nature of thermocAPillary convections.
76 citations
TL;DR: In this article, surface profiles and propagation speeds of the capillary-Marangoni wave along a pendent water drop with a flat ethanol surface or with a sessile drop of ethanol are presented.
Abstract: When two drops of different miscible liquids are brought into contact, their coalescence speed is governed by the liquid having the weaker surface tension. Marangoni waves propagate along the drop with the stronger surface tension. We present surface profiles and propagation speeds of these waves, from experiments with a pendent water drop coalescing with a flat ethanol surface or with a sessile drop of ethanol. We find in the former case that the capillary-Marangoni waves along the water drop show self-similar character when measured in terms of arc length along the original surface. The coalescence of two liquids of different viscosities is also studied. For large viscosity difference, mobility is confined to the lower viscosity fluid and a sharp corner forms where the two liquids meet along the free surface. The coalescence speed of a water drop with a much more viscous liquid is nearly independent of the strength of the viscosity difference.
25 Apr 2007-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, three-dimensional numerical simulations were conducted to study temperature distributions and fluid flows during formation of humped beads in high speed gas metal arc welding (GMAW).
Abstract: Three-dimensional numerical simulations were conducted to study temperature distributions and fluid flows during formation of humped beads in high speed gas metal arc welding (GMAW). Based on simulation and experimental results, the physical mechanisms associated with humping phenomenon were investigated and two conditions responsible for hump formation were identified: the formation of thin liquid channel induced by surface tension pinching force and premature solidification of the melt in the thin channel that divides the weld pool into a front and rear portion. A strong backward fluid flow that produced an accumulation of melt at the rear of the weld pool increased the size of humps. Although surface tension was shown to be important in hump formation, Marangoni flow induced by negative surface tension gradients was not significant for hump formation. The simulation results clarified the fluid flow associated with two different hump shapes. Experimental welds without bead humping were made at a lower travel speed and were also simulated to illustrate the differences in heat and fluid flow from humped beads.
TL;DR: In this article, the steady laminar thermosolutal Marangoni convection in the presence of temperature-dependent volumetric heat sources/sinks as well as of a first-order chemical reaction is considered.
Abstract: The steady laminar thermosolutal Marangoni convection in the presence of temperature-dependent volumetric heat sources/sinks as well as of a first-order chemical reaction is considered in this paper. Assuming that the surface tension varies linearly with temperature and concentration and that the interface temperature and concentration are quadratic functions of the interface arc length x, exact analytical similarity solutions are obtained for the velocity, temperature and concentration fields. The features of these exact solutions as functions of the physical parameters of the problem are discussed in detail.
TL;DR: In this article, the role of intermolecular forces and surface rheology in foam film drainage was investigated and it was shown that non-DLVO hydrophobic attractive forces have the most significant effect on the film drainage.
TL;DR: In this paper, a three-dimensional model describing melting and resolidification of a direct metal laser sintering process under the irradiation of a moving Gaussian laser beam is developed, where effects of shrinkage and natural convection driven by the surface tension and buoyancy force are taken into account.
Abstract: A three-dimensional model describing melting and resolidification of a direct metal laser sintering process under the irradiation of a moving Gaussian laser beam is developed. Effects of shrinkage and natural convection driven by the surface tension and buoyancy force are taken into account. The energy equation is formulated using a temperature-transforming model and solved by the finite-volume method. The temperature distribution and velocity field are investigated. The results show that increasing the initial porosity of the powder bed enlarges the depth of the melt–solid interface and that the laser intensity has great influence on both the depth and width of the liquid pool. The whole molten pool shifts toward the direction opposite the laser scanning as the scanning velocity increases.
TL;DR: In this paper, the development of instabilities under the joint action of van der Waals forces and Marangoni stresses in a two-layer film on a heated or cooled substrate is considered.
Abstract: The development of instabilities under the joint action of the van der Waals forces and Marangoni stresses in a two-layer film on a heated or cooled substrate, is considered. The problem is solved by means of a linear stability theory and nonlinear simulations. Nontrivial change of the droplet shape in the presence of the Marangoni effect, which manifests itself as the deformation of a “plateau” into an “inkpot,” is observed. The appearance of the threshold oscillations predicted by the linear stability theory is confirmed by nonlinear simulations.
TL;DR: In this article, the interplay between a stable horizontal thin liquid film on a solid substrate and an excitable or bistable reactive mixture on its free surface is investigated, and the linear stability of the coupled system as well as the nonlinear behavior, including the propagation of solitary waves, fronts, and pulses are analyzed.
Abstract: We investigate the interplay between a stable horizontal thin liquid film on a solid substrate and an excitable or bistable reactive mixture on its free surface. Their coupling is twofold. On the one hand, flow in the film transports the reacting surfactants convectively. On the other hand, gradients in the surfactant concentration exert Marangoni stresses on the free surface of the film. A reduced model is derived based on the long-wave approximation. We analyze the linear stability of the coupled system as well as the nonlinear behavior, including the propagation of solitary waves, fronts, and pulses. We show, for instance, that the coupling of thin film hydrodynamics and surfactant chemistry can either stabilize instabilities occurring in the pure chemical system, or in a regime where the pure hydrodynamic and chemical subsystems are both stable, the coupling can induce instabilities.
Journal Article•
TL;DR: In this article, the spreading kinetics of aqueous solutions of sodium dodecyl sulfate and trimethyl ammonium bromide along the interface between thick layers of water and decane has been investigated by means of two different optical visualization techniques (dye tracer and laser shadowgraphy).
Abstract: Marangoni-driven spreading at gas-liquid interfaces has been studied extensively over the past years but so far the spreading kinetics along the interface between immiscible liquids has not been investigated systematically. In this study, the spreading kinetics of aqueous solutions of sodium dodecyl sulfate and dodecyl trimethyl ammonium bromide along the interface between thick layers of water and decane has been investigated by means of two different optical visualization techniques (dye tracer and laser shadowgraphy). The spreading kinetics follows a power law where the radius r as function of time t scales as r(t)∝t3/4 indicating large similarities with Marangoni-driven spreading at air-liquid interfaces. The existing scaling law for spreading at air-liquid interfaces is based on the balance between an interfacial tension gradient and the viscous stress in the fluid layers beneath the interface. When the viscous dissipation in the two boundary layers below and above the interface is factored into the scaling law, quantitative agreement with experimental data is obtained. Marangoni-driven spreading along an interface is a fast transport mechanism. The velocity of the leading edge lies within the range of group velocities of capillary waves.
TL;DR: In this paper, a horizontal condenser tube was used to study the Marangoni condensation problem on small vertical plane surfaces, where the appearance of the condensate closely resembles that of dropwise condensation of a pure fluid on a hydrophobic surface.
TL;DR: In this article, experiments on Benard-Marangoni convection are described, which permit a useful understanding of the main concepts involved in this phenomenon such as, Benard cells, aspect ratio, Rayleigh and Marangoni numbers, Crispation number and critical conditions.
Abstract: We describe experiments on Benard–Marangoni convection which permit a useful understanding of the main concepts involved in this phenomenon such as, for example, Benard cells, aspect ratio, Rayleigh and Marangoni numbers, Crispation number and critical conditions. In spite of the complexity of convection theory, we carry out a simple and introductory analysis which has the additional advantage of providing very suggestive experiments. As a consequence, we recommend our device for use as a laboratory experiment for undergraduate students of the thermodynamics of nonlinear and fluid physics.
TL;DR: A phase field model to describe Marangoni convection in a compressible fluid of van der Waals type far from criticality is proposed and a randomly distributed initial density evolves towards phase separation and single droplet formation.
Abstract: Recently we proposed a phase field model to describe Marangoni convection in a compressible fluid of van der Waals type far from criticality [Eur. Phys. J. B 44, 101 (2005)]. The model previously developed for a two-layer geometry is now extended to drops and bubbles. A randomly distributed initial density evolves towards phase separation and single droplet formation. For a two-component liquid-liquid system we report on numerical simulations for drop Marangoni migration in a vertical thermal gradient.
Book•
17 Apr 2007
TL;DR: In this paper, a discussion of instability phenomena driven by the Marangoni effect excitation of isothermal liquid surface instability by variable force fields stabilizing influence of high frequency vibrations on the possible instability of an isothermalliquid surface is presented.
Abstract: A first discussion of instability phenomena driven by the Marangoni effect excitation of isothermal liquid surface instability by variable force fields stabilizing influence of high frequency vibrations on the possible instability of an isothermalliquid surface thermocapillary instability of the free surface of a plane liquid layer convective instability of a liquid layer with a permeable partition thermocapillary instability of two-layer systems with liquid-liquid or liquid-gas interfaces thermocapillary instability in multilayer systems thermocapillary convection of constrained interfaces thermocapillary migration of bubbles and drops spreading and layer breaking driven by the Marangoni effect parametric wave excitation innonisothermal liquid layers thermocapillary instability of a liquid interface under the joint action of high frequency vibration and the Marangoni effect.
TL;DR: In this article, it is shown that the liquid drainage rate is approximately independent of surface dilational viscosity and surface tension (insofar as it creates capillary suction).
TL;DR: In this paper, a variety of controlled flow patterns, including toroidal cells and surface doublets, can be generated in 80-400μm thick liquid films by placing scanning microscopy probes with integrated heaters just above the surface.
Abstract: The authors show that a variety of controlled flow patterns, including toroidal cells and surface doublets, can be generated in 80–400μm thick liquid films by placing scanning microscopy probes with integrated heaters just above the surface ( 1000μm∕s can be accomplished with surface temperature perturbations <1°C. This technique enables microfluidic manipulation on unpatterned substrates.
TL;DR: The dynamics and linear stability of a liquid film flowing over a locally heated surface are studied using a long-wave lubrication analysis, and the structure of optimal perturbation of different wave numbers is computed to elucidate the regions of the film that are most sensitive to perturbations, which provides insight into ways to stabilize the flow.
Abstract: The dynamics and linear stability of a liquid film flowing over a locally heated surface are studied using a long-wave lubrication analysis. The temperature gradient at the leading edge of the heater induces a gradient in surface tension that opposes the gravitationally driven flow and leads to the formation of a pronounced capillary ridge. The resulting free-surface shapes are computed, and their stability to spanwise perturbations is analyzed for a range of Marangoni numbers, substrate inclination angles, and temperature profiles. Instability is predicted above a critical Marangoni number for a finite band of wave numbers separated from zero, which is consistent with published results from experiment and direct numerical simulation. An energy analysis is used to gain insight into the effect of inclination angle on the instability. Because the spatial nonuniformity of the base state gives rise to nonnormal linearized operators that govern the evolution of perturbations, a nonmodal, transient analysis is used to determine the maximum amplification of small perturbations to the film. The structure of optimal perturbations of different wave numbers is computed to elucidate the regions of the film that are most sensitive to perturbations, which provides insight into ways to stabilize the flow. The results of this analysis are contrasted to those for noninertial coating flows over substrates with topographical features, which exhibit similar capillary ridges but are strongly stable to perturbations.
Book•
28 Sep 2007
TL;DR: In this paper, the Lid Driven Container (LDC) Similarity Solutions, Streamlines and Eddies in Planar Flows The New Embedding Method for Complex Geometries The Singular LDC Problem and its Resolution Stokes Flows in special geometries Planar Thermal, Mixed and Thermocapillary (Marangoni) Convection General Features of Three-Dimensional (3D) Flows 3D) Flow in a Cylinder and in a Liquid Bridge 3D Corner Eddies 3D Flow in Rectangular Container
Abstract: Physical Background Least Squares and Eigenfunction Expansions The Lid Driven Container (LDC) Similarity Solutions, Streamlines and Eddies in Planar Flows The New Embedding Method for Complex Geometries The Singular LDC Problem and Its Resolution Stokes Flows in Special Geometries Planar Thermal, Mixed and Thermocapillary (Marangoni) Convection General Features of Three-Dimensional (3D) Flows 3D Flow in a Cylinder and in a Liquid Bridge 3D Corner Eddies 3D Flow in Rectangular Container 3D Thermal Convection in a Cylinder Eddy Structure in an Oscillating LDC Applications to Mixing in LDCs and Viscous Attenuation The Oseen Equations for External Flows Flows Past Bluff Bodies and Arbitrary Streamlined Bodies.
TL;DR: In this paper, the wave characteristics of the water film flow over a vertical or an inclined plate with a heater have been studied and the fluorescence method was used to measure local instantaneous film thickness.
Abstract: Liquid films are encountered in space systems as well as in numerous industrial processes and everyday life. The present work is a part of the preparation of the SAFIR experiment of the European Space Agency onboard the International Space Station. Wave characteristics of the water film flow over a vertical or an inclined plate with a heater have been studied. The fluorescence method was used to measure local instantaneous film thickness. In addition to measure wave characteristics eight capacitance sensors were located as a line across the flow. The process of rivulet formation in a heated film was registered. Two zones of the heat flux effect on liquid film deformation were distinguished. At low heat fluxes, the film flow is hardly deformed. At high heat fluxes the thermocapillary forces provide formation of rivulets and a thin film between them. The measured values of the distance between rivulets depend slightly on the plate inclination angle. It was found that for a positive temperature gradient along the flow, heating may increase the wave amplitude because thermocapillary forces are directed from the valley to the crest of the wave. This effect was shown in the interrivulet zone, where relative wave amplitude and Marangoni number increase with a rise of the heat flux density.
TL;DR: In this article, the effect of the shielding gas concentration on the weld shape was studied for the moving bead on plate TIG welding of SUS304 stainless steel under He-O2 mixed shielding.
Abstract: The effect of the shielding gas concentration on the weld shape was studied for the moving bead on plate TIG welding of SUS304 stainless steel under He–O2 mixed shielding. The small addition of oxygen to the helium base shielding gas can precisely control the oxygen content in a liquid pool and the weld shape. Oxygen is a surface active element for stainless steel. When the oxygen content in the liquid pool is above the critical value of ∼ 70 ppm, the weld shape suddenly changes from a wide shallow type to a deep narrow one due to the change in the Marangoni convection from the outward to inward direction on the liquid pool surface. Weld shape variations influenced by the welding parameters including welding speed, welding current and electrode tip work distance under pure He and He–0.4%O2 mixed gas shielding were systematically investigated. The investigation results showed that the final shape of the TIG weld depends to a large extent on the pattern and magnitude of the Marangoni convection on t...
TL;DR: In this article, the effects of different beam geometries including circular, rectangular and diamond shapes on laser melting of metallic materials were investigated, and the finite volume method was used to simulate the transient effects of a moving beam.
Abstract: Laser melting is an important industrial activity encountered in a variety of laser manufacturing processes, e.g. selective laser melting, welding, brazing, soldering, glazing, surface alloying, cladding etc. The majority of these processes are carried out by using either circular or rectangular beams. At present, the melt pool characteristics such as melt pool geometry, thermal gradients and cooling rate are controlled by the variation of laser power, spot size or scanning speed. However, the variations in these parameters are often limited by other processing conditions. Although different laser beam modes and intensity distributions have been studied to improve the process, no other laser beam geometries have been investigated. The effect of laser beam geometry on the laser melting process has received very little attention. This paper presents an investigation of the effects of different beam geometries including circular, rectangular and diamond shapes on laser melting of metallic materials. The finite volume method has been used to simulate the transient effects of a moving beam for laser melting of mild steel (EN-43A) taking into account Marangoni and buoyancy convection. The temperature distribution, melt pool geometry, fluid flow velocities and heating/cooling rates have been calculated. Some of the results have been compared with the experimental data.
TL;DR: In this paper, the stability of the Rayleigh-Taylor instability of a thin liquid film by the Marangoni effect arising from heating of the liquid at the gas-liquid interface in a bilayer setting is investigated.
Abstract: Stabilization of the Rayleigh-Taylor instability of a thin liquid film by the Marangoni effect arising from heating of the liquid at the gas-liquid interface in a bilayer setting is investigated. Solution of time-dependent Navier-Stokes and long-wave evolution equations in both two and three dimensions shows the emergence of nontrivial nonruptured steady states in the system when the applied temperature gradient exceeds a certain critical value.