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Showing papers on "Marangoni effect published in 2004"


Journal ArticleDOI
TL;DR: In this article, an axisymmetric numerical method to simulate the dynamics of insoluble surfactant on a moving liquid-fluid interface is presented, where the motion of the interface is captured using a volume of fluid method.

237 citations


Journal ArticleDOI
TL;DR: In this article, the role of the oxide layer on the Marangoni convection on the pool surface at elevated temperature has been investigated and it was shown that the heavy oxide layer inhibited the fluid flow induced by the MARANGONA convection and also became a barrier for the oxygen absorption into the molten weld pool.
Abstract: Increasing the oxygen or the carbon dioxide concentration in the argon-based shielding gas leads to an increase in the weld metal oxygen content when the oxygen or carbon dioxide concentration is to be lower than 0.6 vol.% in the shielding gas. However, when the O2 or CO2 concentration is higher than 0.6 vol.% in the Ar-based shielding gas, the weld metal oxygen is maintained around 200 ppm–250 ppm. An inward Marangoni convection mode in the weld pool occurs when the weld metal oxygen content is more than 100 ppm. When it is lower than 100 ppm, the Marangoni convection would change to the outward direction and the weld shape varies from a deep narrow to a shallow wide shape. The effective ranges of O2 and CO2 concentrations for deep penetration are same. A heavy layer of oxides is formed when the O2 or CO2 concentration in the shielding gas is more than 0.6 vol.%. Based on the thermodynamic calculation of the equilibrium reactions of Fe, Si, Cr and Mn with oxygen in liquid iron for the oxide products, FeO, SiO2 ,C r 2O3 and MnO and the experimental oxygen content in the weld metal, Cr2O3 and SiO2 oxides are possibly formed at the periphery area of the liquid pool surface under the arc column during the welding process. One model is proposed to illustrate the role of the oxide layer on the Marangoni convection on the pool surface at elevated temperature. The heavy oxide layer inhibited the fluid flow induced by the Marangoni convection and also became a barrier for the oxygen absorption into the molten weld pool. © 2004 Elsevier B.V. All rights reserved.

140 citations


Journal ArticleDOI
TL;DR: This systematic analysis of the spreading of metal–metal systems with varying degrees of mutual solubility allows this work to report on the fundamental differences between the mechanisms controlling spreading of organic liquids and liquid metals and on formation of Marangoni films driven by surface-tension gradients in high-temperature systems.
Abstract: Despite its apparent simplicity, spreading of liquid metals at high temperatures has defied description and generalization. Wetting at high temperature is usually accompanied by interdiffusion and chemical reaction, but the forces that drive reactive spreading and the mechanisms that control its kinetics have been very poorly understood. The unsolved challenge has been to link macroscopic measurements such as the dynamic contact angle or the speed of a moving liquid front to phenomena occurring at the microscopic and even atomic level in the vicinity of the triple solid-liquid-vapour junction. We have taken a big step towards meeting this challenge. Our systematic analysis of the spreading of metal-metal systems with varying degrees of mutual solubility allows us to report on the fundamental differences between the mechanisms controlling spreading of organic liquids and liquid metals and on formation of Marangoni films driven by surface-tension gradients in high-temperature systems.

128 citations


Book
27 Dec 2004
TL;DR: Wesdorp et al. as discussed by the authors used 3D Wide Field Transmitted Polarized Light Microscopy and Image Deconvolution (WFLM) to image a model of a model plastic fat system.
Abstract: Crystallography AG Marangoni Crystallization Kinetics AG Marangoni Lipid Phase Behavior K L Humphrey and SS Narine Rheology Fundamentals and Structural Theory of Elasticity AG Marangoni and SS Narine Viscoelasticity AG Marangoni Dynamic Methods AG Marangoni Microstructure SS Narine and AG Marangoni The Yield Stress and Elastic Modulus of a Fat Crystal Network AG Marangoni Experimental Methodology R Campos Scaling Behavior of the Elastic Modulus in Colloidal Networks of Fat Crystals TS Awad, MA Rogers and AG Marangoni Comparison Between Image Analyses Methods for the Determination of the Fractal Dimension of Fat Crystal Networks TS Awad and AG Marangoni The Nature of Fractility in Fat Crystal Networks AG Marangoni Identifying Key Indicators of Mechanical Strength in Mixtures of Milk Fat Fractions and Cocoa Butter AG Marangoni and SS Narine The Functionality of Milk Fat Fractions in Confectionery and Plastic Fats AG Marangoni Liquid-Multiple Solid Phase Equilibria in Fats: Theory and Experiments LH Wesdorp, JA van Meeteren, S de Jong, R Giessen, P Overbosch, PAM Grootscholten, M Struik, E Royers, A Don, T de Loos, C Peters, and I Gandasasmita Imaging of a Model Plastic Fat System by 3-Dimensional Wide-Field Transmitted Polarized Light Microscopy and Image Deconvolution JW Litwinenko Index

127 citations


01 Jan 2004
TL;DR: In this article, a systematic analysis of the spreading of metal-metal systems with varying degrees of mutual solubility is presented, and fundamental differences between the mechanisms controlling spreading of organic liquids and liquid metals and on formation of Marangoni fi lms driven by surface-tension gradients in high-temperature systems are reported.
Abstract: Despite its apparent simplicity, spreading of liquid metals at high temperatures has defi ed description and generalization. Wetting at high temperature is usually accompanied by interdiffusion and chemical reaction, but the forces that drive reactive spreading and the mechanisms that control its kinetics have been very poorly understood. The unsolved challenge has been to link macroscopic measurements such as the dynamic contact angle or the speed of a moving liquid front to phenomena occurring at the microscopic and even atomic level in the vicinity of the triple solid‐liquid‐vapour junction. We have taken a big step towards meeting this challenge. Our systematic analysis of the spreading of metal‐metal systems with varying degrees of mutual solubility allows us to report on the fundamental differences between the mechanisms controlling spreading of organic liquids and liquid metals and on formation of Marangoni fi lms driven by surface-tension gradients in high-temperature systems.

104 citations


Journal ArticleDOI
TL;DR: By employing continuous Gaussian laser irradiation in tandem with a specifically designed drop-on-demand jetting system, nanoparticle inks were printed and sintered on glass substrate.
Abstract: By employing continuous Gaussian laser irradiation in tandem with a specifically designed drop-on-demand jetting system, nanoparticle inks were printed and sintered on glass substrate A toluene solvent is employed as the carrier of gold nanoparticles possessing a lower melting temperature than that of bulk gold Marangoni flow due to radial surface tension gradient combined with a moving substrate displaces nanoparticle ink in front of and around the laser spot Experiments were carried out changing incident laser power, focused beam waist, and translation speed, and resulting phenomena at different conditions were explained Strong coalescence occurred from 9000–14000 W/cm2, and a gold line with 8 μm of width was demonstrated

95 citations


Journal ArticleDOI
TL;DR: In this article, the effect of insoluble surfactants on the stability of the gravity-driven flow of a liquid film down an inclined plane was investigated by normal-mode analysis, and numerical solutions of the Orr-Sommerfeld equation reveal the occurrence of a stable Marangoni mode and a possibly unstable Yih mode.
Abstract: The effect of an insoluble surfactant on the stability of the gravity-driven flow of a liquid film down an inclined plane is investigated by a normal-mode analysis. Numerical solutions of the Orr–Sommerfeld equation reveal the occurrence of a stable Marangoni mode and a possibly unstable Yih mode, and demonstrate that the primary role of the surfactant is effectively to raise the critical Reynolds number at which instability is first encountered.

92 citations


Journal ArticleDOI
TL;DR: In this paper, the evaporation process from a liquid meniscus formed in capillary tubes of various sizes is investigated; a very strong convection within the liquid phase is observed.

90 citations


Journal ArticleDOI
TL;DR: In this article, a study of adsorbed and applied fluid movement on a solid surface driven by surface tension gradients created by thermal gradients is presented, where flexible control over the silicone oil and 1,3,5 trinitrotoluene movement is accomplished with an array of individually controllable gold thin film thermal elements on a fused silica substrate surface.
Abstract: A convective flow system is engendered when two liquid droplets, or a liquid droplet and a solid surface, are maintained at different temperatures. Such flows give rise to Marangoni forces which under proper conditions prevent droplet coalescence, cause fluid motion, and dewetting. We present a study of adsorbed and applied fluid movement on a solid surface driven by surface tension gradients created by thermal gradients. Flexible control over the silicone oil and 1,3,5-trinitrotoluene movement is accomplished with an array of individually controllable gold thin film thermal elements on a fused silica substrate surface. We thus demonstrate unlimited fluid movements in one dimension.

83 citations


Journal ArticleDOI
TL;DR: In this article, a combined experimental and numerical analysis has been carried out to study Marangoni effects during the evaporation of droplets, where the experiments were performed with pendant drops of silicone oils (with different viscosities) and hydrocarbons.
Abstract: A combined experimental and numerical analysis has been carried out to study Marangoni effects during the evaporation of droplets. The experiments are performed with pendant drops of silicone oils (with different viscosities) and hydrocarbons. The temperature of the disk sustaining the drop is rapidly increased or decreased in order to study transient heating or cooling processes. The velocity field in the droplet is evaluated monitoring the motion of tracers in the meridian plane, using a laser sheet illumination system and a video camera. Surface temperature distributions of the drops are detected by infrared thermocamera. The numerical model is based on axisymmetric Navier–Stokes equations, taking into account the presence of Marangoni shear stresses and evaporative cooling at the liquid-air interface. Marangoni flows cause a larger, more uniform surface temperature, increasing heat transfer from disk to droplet, as well as evaporation rate. When Marangoni effects are negligible, larger surface temperature differences occur along the drop surface and heat transfer is relatively small. The role of Marangoni and buoyancy flows in silicone oils with different viscosities and hydrocarbons is discussed and correlations are presented between experimental and numerical results.

82 citations


Journal ArticleDOI
TL;DR: In this paper, the formation of standing waves at the surfactant-covered free surface of a vertically-vibrated liquid is analyzed, and linear stability analysis and Floquet theory are applied to the governing equations.
Abstract: The formation of standing waves at the surfactant-covered free surface of a vertically-vibrated liquid is analyzed in this work. Assuming that the surfactants are insoluble and the effects of lateral boundaries are negligible, linear stability analysis and Floquet theory are applied to the governing equations. A recursion relation involving the temporal modes of the free-surface deflection and surfactant concentration variation results, and is solved to determine the critical vibration amplitude needed to excite the standing waves and the corresponding critical wave number. It is found that the critical vibration amplitude shows a minimum with respect to the Marangoni number, meaning that surfactants can potentially lower the value of the critical amplitude relative to its value for an uncontaminated free surface. The critical wave number, however, is found to be an increasing function of the Marangoni number. Analysis of the phase-angle difference between the free-surface deflection and the surfactant concentration variation suggests that the minimum in the critical amplitude arises because the Marangoni flows help produce a velocity field near the free surface similar to that which would be present if the liquid were inviscid.

Journal ArticleDOI
TL;DR: In this paper, a heat transfer model was developed in order to explain the phenomena observed in nucleate pool boiling, and the results indicated that Marangoni convection associated with the bubbles formed by the air dissolved in the water which emerged from solution when the water was heated sufficiently, significantly influenced the heat transfer rate in subcooled nucleate pools boiling.

Journal ArticleDOI
TL;DR: In this article, the effect of insoluble surfactant on the stability of two-layer viscous flow in an inclined channel confined by two parallel walls is considered, and a lubrication-flow model applicable to long waves and low Reynolds-number flow is developed, and pertinent nonlinear evolution equations for the interface position and surface concentration are derived.
Abstract: The effect of an insoluble surfactant on the stability of two-layer viscous flow in an inclined channel confined by two parallel walls is considered. A lubrication-flow model applicable to long waves and low-Reynolds-number-flow is developed, and pertinent nonlinear evolution equations for the interface position and surfactant concentration are derived. Linear stability analysis based on the lubrication-flow model and the inclusive equations of Stokes flow confirm the recent findings of Frenkel & Halpern (2002) and Halpern & Frenkel (2003) that the presence of an insoluble surfactant induces a Marangoni instability in certain regions of parameter space defined by the layer thickness and viscosity ratios. Numerical simulations based on both approaches show that the interfacial waves may grow and saturate into steep profiles. The lubrication-flow model is adequate in capturing the essential features of the instability for small and moderate wavenumbers.

Journal ArticleDOI
TL;DR: In this article, the authors present a theory based on the lubrication approximation, capable of explaining the physical mechanism responsible for these phenomena and the trends observed experimentally, which is achieved via use of a nonlinear equation of state.
Abstract: A striking fingering instability accompanies surfactant droplet deposition upon thin films. The fingers apparently emerge from the droplet and are preceded by a circular rim of thickened fluid. In this work, we present a theory, based on the lubrication approximation, capable of explaining the physical mechanism responsible for these phenomena and the trends observed experimentally. The model comprises evolution equations for the film thickness and surfactant interfacial and bulk concentrations, which are parametrized by appropriately defined solubility and sorption kinetics parameters, and surface and bulk Peclet numbers; closure is achieved via use of a nonlinear equation of state. The results of our transient growth analysis and two-dimensional numerical simulations illustrate the delicate interplay, which exists between surfactant solubility and the nonlinearity in the equation of state. In particular, we show that solubility acts to destabilize the spreading process for a given value of the nonlinearity except for very highly soluble surfactants. In this case, the magnitude of the Marangoni stresses available to drive spreading and instability diminishes leading to flow stability.

Journal ArticleDOI
TL;DR: In this article, the influence of a surfactant on the mass transfer of CO2-water was investigated and the Schlieren method and a three-mode magnetic suspension balance connected to an optical cell were used to analyse the CO2 mass transfer.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the effect of temperature and solutal driven changes of surface tension on pattern formation at the interface between two immiscible fluids filling a Hele-Shaw cell, each containing a reactant of an exothermic neutralization reaction.
Abstract: This article is devoted to the investigation of Marangoni-driven pattern formation at the interface between two immiscible fluids filling a Hele-Shaw cell, each of them containing a reactant of an exothermic neutralization reaction. In such a system, convective patterns arise when one reactant diffuses through the interface to react with the other chemical species in one of the fluids. A chemo-hydrodynamical pattern appears due to Marangoni instabilities taking place because of heat and solutal driven changes of the surface tension. The mathematical model we develop consists in a set of reaction-diffusion-advection equations ruling the evolution of concentrations and temperature coupled to Navier–Stokes equation, written in a Hele-Shaw approximation. In our analysis, the time-dependent convectionless reaction-diffusion base state is first obtained and studied in detail. Next, we perform a linear stability analysis of this base state with regard to thermal and solutal Marangoni effects to determine the parameter values beyond which convection occurs. Finally, we perform numerical simulations of the fully nonlinear system and study the influence of the different parameters on pattern formation.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the self-motion of a camphor disk on water and found that it exhibited a characteristic motion that depended on the shape of the base of the chamber.
Abstract: The self-motion of a camphor disk on water was investigated both experimentally and theoretically. When the camphor disk moved along a one-dimensional water chamber, a convective flow was observed around the disk and the magnitude of convection decreased with an increase in the velocity of camphor motion. The camphor disk exhibited a characteristic motion that depended on the shape of the base of the chamber. The nature of the self-motion was reproduced by a numerical simulation that included the surface tension of the camphor layer as the driving force and Marangoni convection induced by the difference in surface tension around the camphor disk.

Journal ArticleDOI
TL;DR: In this paper, the effect of the drop-scale Marangoni effect with the sub-drop-scale local interfacial convection is investigated numerically, showing that the effect occurs only when the surface tension sensitivity to the solute concentration variation is above certain critical level.

Journal ArticleDOI
TL;DR: In this article, the effects of vapor fluid dynamics on the interfacial instability that occurs during evaporation were investigated and it was concluded that the vapor flow stabilizes while the liquid flow destabilizes the evapation problem when heated from the liquid side.
Abstract: Linear stability analysis is used to describe the effects of vapor fluid dynamics on the interfacial instability that occurs during evaporation. Evaporation is considered in a liquid layer underlying its own vapor, and both fluid layers are assumed to be of finite depth. The physics are initially described without Marangoni and gravitational effects. Later, these effects are sequentially added to the problem. It is concluded that the vapor flow stabilizes while the liquid flow destabilizes the evaporation problem when heated from the liquid side. These conclusions are supported by calculations.

Journal ArticleDOI
TL;DR: A series of microgravity experiments on self-rewetting fluids has been conducted at the 10-second drop shaft of the Japan Microgravity Center (JAMIC) in this article.
Abstract: A series of microgravity experiments on self-rewetting fluids has been conducted at the 10-second drop shaft of the Japan Microgravity Center (JAMIC). In all the experiments, 1.5 wt% of 1-butanol aqueous solution were employed as a self-rewetting fluid. The objective of the first experiment was to observe the boiling behavior of two-dimensional adjacent dual vapor bubbles with the aid of a two-wavelength interferometer and tracer particles. A significant difference was observed between a self-rewetting fluid and a normal fluid (CFC-113 in this experiment) in bubble interaction and flow developed along vapor/bubble interface. The second experiment focused on the flow at the bubble/heater contact area and around the three-phase interline, visualized with tracer particles. Differing behavior among three fluids, 1-butanol aqueous solution, CFC-113, and ethanol aqueous solution, was observed. The last microgravity experiment was a demonstration of wickless heat pipes containing three different fluids as a working fluid, 1-butanol aqueous solution, water, and ethanol aqueous solution. The temperature variation of working fluid in the heat pipe was monitored, and the liquid flow returning from the condensation region to the evaporation region was visualized by tracer particles. In addition to microgravity experiments, the performance of conventional heat pipes with 1-butanol aqueous solution was evaluated on the ground, and compared with water heat pipes. Our preliminary results are presented.

Journal ArticleDOI
TL;DR: In this article, a fundamental study on the movement of various sized micro-liter droplets on a surface subjected to temperature gradients is presented, where the histories of droplet movement are recorded by high-speed CCD camera and are simulated by numerical methods based on first principle equations.
Abstract: This work is a fundamental study on the movement of various sized micro-liter droplets on a surface subjected to temperature gradients The histories of droplet movement are recorded by high-speed CCD camera and are simulated by numerical methods based on first principle equations The agreement between computations and experimental observations are obtained The study indicates that temperature gradients, the change of dynamic receding/advancing contact angles across the droplets, and the flowfields inside the droplet are the key parameters determining the moving behavior of the micro-droplet driven by Marangoni and capillary effects

Journal ArticleDOI
TL;DR: It was found that water droplets on an aluminum surface exhibit a 'depinning jump' at subatmospheric pressures, thought that the local concentration of the surfactant causes a gradient of surface tension.

Journal ArticleDOI
TL;DR: In this article, a 3D model is implemented in the finite element software calcosoft in order to model the development of the fluid convection within the liquid pool and the local solidification conditions such as thermal gradient and the solidification speed can be extracted at both the solidus and liquidus temperatures to assess the risk of CET and hot cracking.
Abstract: Epitaxial Laser Metal Forming (E-LMF) consists in impinging a jet of metallic powder onto a molten pool formed by controlled laser heating and thereby, generating epitaxially a single crystal deposit onto the damaged component. This new technique aims to be used for the repair and reshape single crystal gas turbine components. Because of the very localised melting pool, the high temperature gradients produced during the process must be carefully controlled in order to avoid both the columnar-to-equiaxed transition (CET) and the appearance of hot tears. To this end, heat flow modelling is required to establish the relationship between process parameters such as laser power, beam diameter and scanning speed, and the local solidification conditions. When modelling the heat transfer within the sample, it is necessary to include the liquid flow pattern generated by the surface tension driven convection known as the Marangoni effect. Indeed, the fluid flow in the liquid pool dictates the shape of the traces as shown by the measurements carried out at EPF-Lausanne in re-melting experiments. A three dimensional (3D) model is implemented in the finite element software calcosoft in order to model the development of the fluid convection within the liquid pool. It is shown that the velocities due to natural convection are of the order of 1 mm/sec whereas Marangoni convection produces velocities of the order of 1 m/sec. Moreover, at low scanning speeds, the liquid pool becomes larger than the beam diameter and the development of Marangoni eddies leads to a widening and deepening of the pool. The local solidification conditions such as the thermal gradient and the solidification speed can be extracted at both the solidus and liquidus temperatures to assess the risk of CET and hot cracking.

Journal ArticleDOI
TL;DR: In this article, the effect of inertia on the Yih-Marangoni instability of the interface between two liquid layers in the presence of an insoluble surfactant was assessed for shear-driven channel flow by a normal-mode linear stability analysis.
Abstract: The effect of inertia on the Yih–Marangoni instability of the interface between two liquid layers in the presence of an insoluble surfactant is assessed for shear-driven channel flow by a normal-mode linear stability analysis. The Orr–Sommerfeld equation describing the growth of small perturbations is solved numerically subject to interfacial conditions that allow for the Marangoni traction. For general Reynolds numbers and arbitrary wave numbers, the surfactant is found to either provoke instability or significantly lower the rate of decay of infinitesimal perturbations, while inertial effects act to widen the range of unstable wave numbers. The nonlinear evolution of growing interfacial waves consisting of a special pair of normal modes yielding an initially flat interface is analysed numerically by a finite-difference method. The results of the simulations are consistent with the predictions of the linear theory and reveal that the interfacial waves steepen and eventually overturn under the influence of the shear flow.

Journal ArticleDOI
TL;DR: In this paper, the deformation of the free melt-gas interface due to the gravity field is taken into account, and the results of the analysis are shown that the interplay between the upper half and lower half of the liquid domain is an essential factor for the correct description of the phenomena under investigation.
Abstract: The present paper strongly extends a previous analysis dealing with the investigation of the three-dimensional Marangoni flow instability in cylindrical floating zones (straight liquid column of full-zone extent) of a low Prandtl liquid laterally heated by a ring positioned around the equatorial plane and under microgravity conditions. The new study gives insights into the combined influence of volume and gravitational effects. The deformation of the free melt–gas interface due to the gravity field is taken into account. Parallel supercalculus is used to reduce the otherwise prohibitive computational time. The prominent features of the three-dimensional field are largely dependent on geometrical parameters. The results (full zone) are heretofore unseen and show that the interplay between the upper half and lower half of the liquid domain is an essential factor for the correct description of the phenomena under investigation. They are contrasted with the case of the half zone for which a rich variety of interesting and worthy contributions is available in literature.

Journal ArticleDOI
TL;DR: In this paper, the electric potential and interfacial tension were simultaneously recorded in a water−oil−water system (cetyltrimethylammonium bromide (CTAB) in water/picric acid in dichloromethane/water).
Abstract: Oscillations of the electric potential and of the interfacial tension were simultaneously recorded in a water−oil−water system (cetyltrimethylammonium bromide (CTAB) in water/picric acid in dichloromethane/water). Both types of oscillations were perfectly correlated in time and shape. In each oscillatory cycle, the fast jumps in the electric potential are related to a rapid adsorption of the surfactant at the interface while the slow motion relaxations correspond to the liberation of the interface from the surfactant by the formation of hydrophobic cetyltrimethylammonium picrate ion pairs that diffuse into the CH2Cl2 phase. The fast inflow of CTAB to the interface is probably caused by periodically occurring convective Marangoni instabilities. The transitions to the convective regime are assumed to be controlled by the fractional surfactant coverage of the interface.

Journal ArticleDOI
TL;DR: In this article, a model is proposed to illustrate the interaction between CO2 gas and the molten pool in the welding process, and an inward Marangoni convection occurs when the oxygen content in the weld pool is over 80 ppm.
Abstract: Small CO2 additions of 0.092 to 10 vol pct to the Ar shielding gas dramatically change the weld shape and penetration from a shallow flat-bottomed shape, to a deep cylindrical shape, to a shallow concave-bottomed shape, and back to the shallow flat-bottomed shape again with increasing CO2 additions in gas thermal arc (GTA) welding of a SUS304 plate. Oxygen from the decomposition of CO2 transfers and becomes an active solute element in the weld pool and reverses the Marangoni convection mode. An inward Marangoni convection in the weld pool occurs when the oxygen content in the weld pool is over 80 ppm. Lower than 80 ppm, flow will change to the outward direction. An oxide layer forms on the weld pool in the welding process. The heavy oxide layer on the liquid-pool surface will inhibit the inward fluid flow under it and also affects the oxygen transfer to the liquid pool. A model is proposed to illustrate the interaction between the CO2 gas and the molten pool in the welding process.

Journal ArticleDOI
TL;DR: A chemical oscillatory phenomenon which occurs as follows: a pendant drop of water is immersed in a viscous oil, both phases containing reagents which react to produce a surfactant at the interface.
Abstract: We describe a chemical oscillatory phenomenon which occurs as follows: a pendant drop of water is immersed in a viscous oil, both phases containing reagents which react to produce a surfactant at the interface. As the drop falls away from the tip of a small needle, the remaining interface spontaneously elongates into a sharp cone and ejects small droplets from the pointed tip. The tip then either contracts and re-elongates periodically, or remains steadily elongated. Small droplets continue to be ejected in either case, and the phenomenon persists over a period of tens of minutes. Quantitative measurements connect these chemically driven phenomena with studies in four-roll mills. A mechanism is proposed by which these phenomena are sustained by Marangoni stresses.

Journal ArticleDOI
TL;DR: In this article, it was shown that for inlet ammonia concentrations in the range 0.2-0.9 wt.% the average condensation heat transfer for the condenser was enhanced by up to 14%.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate the motion of liquids induced by surface tension gradients generated by local heating by bringing a heat source (soldering iron) close to a thin liquid film in a Petri dish, where the motions are easily observable owing to the rupture of the film.
Abstract: This article presents a simple experiment to demonstrate the motion of liquids induced by surface tension gradients generated by local heating. Changes in temperature are produced by bringing a heat source (soldering iron) close to a thin liquid film in a Petri dish, where the motions are easily observable owing to the rupture of the film. The experiment is easy to perform, and the visualization of the effect can facilitate the introduction of surface tension gradients. The use of other heat sources and some of the possible variations of this experiment are also mentioned.Find this demonstration and others in the DigiDemos area of the JCE Digital Library.