Showing papers on "Marangoni effect published in 1990"
TL;DR: In this paper, the authors report another example of such unstable driven flow, this time caused by the Marangoni effect, in which a temperature gradient induces a gradient of surface tension which drives the spreading process.
Abstract: THE dynamics of spreading of thin liquid films are important to many technological and biological processes, including tertiary oil recovery, coating processes, the formation and protection of microchips and biological cell interactions. The spontaneous spreading of thin liquid films under capillary forces alone is typically a slow process. An applied force—gravitational or centrifugal, or a surface shear stress—can be used to drive the spreading more quickly1,2. Recent experimental3,4 and theoretical5 studies have revealed that in all of these cases of forced spreading, the liquid front undergoes a fingering instability. Here we report another example of such unstable driven flow, this time caused by the Marangoni effect6, in which a temperature gradient induces a gradient of surface tension which drives the spreading process.
385 citations
TL;DR: In this article, the authors investigate the flow induced by a localized insoluble surfactant on a thin film and derive equations that describe the evolution of the film thickness and surface tension.
Abstract: We investigate the flow induced by a localized insoluble surfactant on a thin film. This problem is intended to model the behaviour of the lung's thin-film lining after an aerosol droplet lands on its surface. The surfactant-induced surface-tension gradients drive convection (Marangoni convection) within the film, disrupting the film surface and causing the surfactant to spread. The surfactant may also spread on the film's surface by surface diffusion without inducing convection. Gravity provides a restoring force that decreases film disturbances.Lubrication theory is employed to derive equations that describe the evolution of the film thickness and surfactant concentration. A nonlinear surface-tension equation of state describes the relationship between the surfactant concentration and the surface tension. Solutions of the evolution equations are found numerically using the method of lines and analytically under limiting cases of small and large surface diffusivity. The results elucidate the behaviour of the thin-film/surfactant system.We find that surface-tension-induced convection creates film disturbances that increase the film thickness near the surfactant's leading edge, and thins the film in the central region. Surface diffusion causes more rapid spreading of the surfactant, and decreases the film disturbances. Gravity decreases the film disturbances by creating bi-directional flow in the form of a ring vortex. This behaviour may have implications for the delivery of medications or toxins by aerosol inhalation.
238 citations
TL;DR: In this article, the authors carried out an asymptotic analysis for different convective, diffusive and kinetic timescales and showed that, if transport in the film is mass-transfer limited such that a bulk concentration gradient exists, the film thickness increases by a maximum factor of 4 2/3; over Bretherton's mobile result at low bubble speeds.
Abstract: When a viscous liquid is displaced by a long air bubble in a capillary, it leaves behind a wetting liquid film. A lubrication analysis by Bretherton (1961), which assumes a mobile surface, underpredicts the film thickness at low bubble speeds. In this investigation, the Marangoni effect of small amounts of impurities is shown to be capable of explaining this discrepancy. We carry out an asymptotic analysis for different convective, diffusive and kinetic timescales and show that, if transport in the film is mass-transfer limited such that a bulk concentration gradient exists in the film, the film thickness increases by a maximum factor of 4 2/3; over Bretherton's mobile result at low bubble speeds. Moreover, at large bubble speeds, Bretherton's mobile prediction is approached for all ranges of timescales. For intermediate bubble speeds, the film thickness varies with respect to the bubble speed with an exponent smaller than 2/3 of the mobile theory. These results are favourably compared to literature data on film thickness.
202 citations
TL;DR: It is shown that the Marangoni effect drives the fingering instability observed at the edge of an aqueous surfactant drop spreading on a thin film of water via a mechanism mathematically similar to that in Hele-Shaw flow despite the very different underlying physics.
Abstract: We show that the Marangoni effect drives the fingering instability observed at the edge of an aqueous surfactant drop spreading on a thin film of water. A calculation of the unperturbed flow profile demonstrates that the spreading of the drop is controlled by the dynamics of a thin layer which develops in front of the drop. The surface-tension gradient in this region leads to the fingering instability via a mechanism mathematically similar to that in Hele-Shaw flow despite the very different underlying physics.
151 citations
TL;DR: Marangoni drying as mentioned in this paper is a new drying process in which the substrate to be dried is withdrawn from a rinse bath (water) while at the same time nitrogen gas with a trace of an organic vapor is led along its surface.
Abstract: In a new drying process (referred to as Marangoni drying), the substrate to be dried is withdrawn from a rinse bath (water) while at the same time nitrogen gas with a trace of an organic vapor is led along its surface The organic vapor dissolves into water and introduces a surface tension gradient in the wetting film on the substrate, causing the water film to quickly drain backwards into the rinse batch (a Marangoni effect) As a result, a completely dry substrate emerges from the bath Contrary to spin drying, almost no contamination is added to the substrate surface during drying
124 citations
TL;DR: In this paper, the time dependent thermocapillary flow in floating half-zones has been investigated experimentally under microgravity and under normal gravity by heating from above and from below.
67 citations
TL;DR: In this paper, a population balance model is presented for the coarsening of the dispersed phase of liquid-liquid two-phase mixtures in microgravity due to gravity sedimentation and Marangoni migration, which lead to the collision and coalescence of droplets.
Abstract: A population balance model is presented for the coarsening of the dispersed phase of liquid-liquid two-phase mixtures in microgravity due to gravity sedimentation and Marangoni migration, which lead to the collision and coalescence of droplets. The model is used to predict the evolution of the size distribution of the dispersed phase in a liquid-phase miscibility gap system, Zn-Bi, which has been used in a number of experimental microgravity processing studies in which significant phase segregation has been observed. The analysis shows that increasing the temperature gradient, gravity level, volume fraction of the dispersed phase, initial average drop radius, initial standard deviation of droplet radii, or the temperature coefficient of the interfacial tension leads to an increase in the rate of droplet growth due to collision and coalescence. Comparison of the distribution evolutions for unimodal and bimodal initial distributions shows that the latter yield significantly more rapid droplet growth. Finally, it is shown that droplet growth can be dramatically reduced with antiparallel orientation of the gravity vector and the temperature gradient, provided that the relative magnitude of these two vectors is properly chosen.
67 citations
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01 Jan 1990
TL;DR: In this article, the authors presented a simulation of buoyancy-driven Oscillatory Flows in Shallow Cavities Filled With Low-Prandtl Number Fluids using the TURBIT Code.
Abstract: Benchmark Definition.- 1. Finite Difference Methods.- Fine Mesh Solutions Using Stream Function-Vorticity Formulation.- A Comparison of Velocity-Vorticity and Stream Function-Vorticity Formulations for Pr=0.- Buoyancy-Driven Oscillatory Flows in Shallow Cavities Filled With Low-Prandtl Number Fluids.- A Finite-Difference Method With Direct Solvers for Thermally-Driven Cavity Problems.- Contribution to the GAMM Workshop.- Low Prandtl Number Convection in a Shallow Cavity.- Numerical Simulation of Oscillatory Convection in Low Prandtl Number Fluids With the TURBIT Code.- Marangoni Flows in a Cylindrical Liquid Bridge of Silicon.- Numerical Simulation of Oscillatory Convection in a Low Prandtl Fluid.- Steady-State Natural Convection in a Rectangular Cavity Filled With Low Prandtl Number Fluids.- Numerical Simulation of Oscillatory Convection in Low Prandtl Number Fluids Using AQUA Code.- Pressure Correction Splitting Methods for the Computation of Oscillatory Free Convection in Low Pr Fluids.- Influence of Thermocapillarity on the Oscillatory Convection in Low-Pr Fluids.- 2. Finite Volume Methods.- Numerical Simulation of Oscillatory Convection in Low-Pr Fluids.- An Implicit Pressure Velocity Algorithm Applied to Oscillatory Convection in Low Prandtl Fluid.- Oscillatory Natural Convection in a Long Horizontal Cavity.- Contribution of the Heat-Transfer Group at DELFT University.- Numerical Simulation of Oscillatory Convection in Low Prandtl Fluids.- 3. Finite Element Methods.- Application of the N3S Finite Element Code to Simulation of Oscillatory Convection in Low Prandtl Fluids.- Two- and Three-Dimensional Finite Element Simulations of Buoyancy-Driven Convection in a Confined Pr=0.015 Liquid Layer.- Two and Three-Dimensional Study of Convection in Low Prandtl Number Fluids.- Numerical Simulation of Oscillatory Convection in Low Prandtl Fluids.- The Solution of the Boussinesq Equations by the Finite Element Method.- Numerical Simulation of Oscillatory Convection in Low Pr Fluids by Using the Galerkin Finite Element Method.- 4. Spectral Methods.- Oscillatory Convection in Low Prandtl Fluids: A Chebyshev Solution With Special Treatment of the Pressure field.- Contribution to the GAMM Workshop With a Pseudo-Spectral Chebyshev Algorithm on a Staggered Grid.- Spectral Calculations of Convection in Low-Pr Fluids.- Spectral Method for Two-Dimensional Time-Dependent Pr?0 Convection.- Steady-State Solution of a Convection Benchmark Problem by Multidomain Chebyshev Collocation.- 5. Synthesis.- Synthesis of Finite Difference Methods.- Synthesis of the Results With the Finite-Volume Method.- Analysis of Finite Element Results.- Analysis of Spectral Results.- General Synthesis of the Numerical Results.- 6. Stability Results.- Linear and Non-Linear Analysis of the Hadley Circulation.- A Bifurcation Analysis of Oscillatory Convection in Liquid Metals.- 7. Experimental Results.- A Laboratory Study of Oscillations in Differentially Heated Layers of Mercury.- Subharmonic Transitions in Convection in a Moderately Shallow Cavity.- Convection in a Shallow Cavity.- Conclusions.- List of Participants.- Support and Sponsoring Acknowledgements.
53 citations
TL;DR: In this paper, the origin of strictly periodic, non-rotational W striations in Mo single crystals grown by electron beam float-zoning was investigated through a systematic variation of crystal growth parameters, the periodic striations were shown to be due to the transition of the thermocapillary flow from a steady to a single-mode oscillatory state.
51 citations
TL;DR: In this paper, the authors considered the case of exchange of stability as a special case of overstability and provided a generalization of Takashima's work concerning a pure Marangoni mechanism (with less general conditions).
Abstract: Overstability for simultaneous surface‐tension‐ and buoyancy‐driven instability in a horizontal infinite liquid layer is theoretically investigated by means of a small disturbance analysis. Formulation and results are given in dimensionless forms. Critical wavenumbers, time constants, and Marangoni numbers are computed. Besides the influence of Prandtl, Bond, and crispation numbers, the modifications induced by interfacial viscosities, heat transfer at the free surface, buoyancy with respect to a pure Marangoni mechanism, and different thermal conditions at the rigid wall, are included in the analysis. The case of exchange of stability is considered as a special case of overstability. This work provides a generalization of Takashima’s work [J. Phys. Soc. Jpn. 50, 2745, 2751 (1981)] concerning a pure Marangoni mechanism (with less general conditions).
41 citations
TL;DR: In this article, the authors used particle image-velocimetry for flow visualization and analysis, which offers the advantage of measuring the entire flow field (velocity field, streamlines etc) in a selected plane within the fluid at a given instant of time.
Abstract: Thermocapillary convection is studied experimentally using particle-image-velocimetry for flow visualization and analysis This method offers the advantage of measuring the entire flow field (velocity field, streamlines etc) in a selected plane within the fluid at a given instant of time in contrast to point by point methods like laser-Doppler-velocimetry (LDV) The paper describes the method and presents quantitative results for different Marangoni numbers
TL;DR: In this paper, the motion of a nitroethane lens located at the surface of an aqueous solution of dodecyltrimethylammonium bromide is analyzed.
TL;DR: In this paper, the surface temperature of stationary molten zones in Mo and Nb rods was measured as a function of the heating power at well defined stability limits, singlemode temperature oscillations were detected.
TL;DR: In this article, the authors considered thermocapillary convection in a rectangular cavity with a top 287 free surface and found the solutions that describe the thermocAPillary convections and interface shape of the free surface iteratively for both fixed heights and fixed angles of the contact between the free surfaces and the solid side walls.
Abstract: Thermocapillary convection in a rectangular cavity with a top 287free surface has been, considered. The top free surface of the cavity is subjected to inhomogeneous heating, which generates a bulk fluid motion. The Navier-Stokes equations and the energy equation have been solved by a finite-difference method with a boundary-fitted curvilinear coordinate system, which is generated numerically and always places the coordinate line coincident with the current boundary surfaces. The solutions that describe the thermocapillary convection and interface shape of the free surface are found iteratively for both fixed heights and fixed angles of the contact between the free surface and the solid side walls. The influence of the capillary, Reynolds, and Prandtl numbers on the flow field, the temperature distribution, and the free-surface deformation is considered. The results for a shallow cavity with small capillary, Reynolds, and Marangoni numbers are in qualitative and quantitative agreement with the previous asy...
TL;DR: In this article, the influence of surface tension on the flow and heat transfer in the liquid phase as well as the resultant shape and motion of the solid-liquid interface is investigated for the melting of a pure metal from an isothermal vertical wall.
TL;DR: In this article, the authors present a stability diagram for liquid columns with free fluid surfaces, which are supported by surface tension only, in the microgravity environment within the Space Station Mir, within the Spacelab, and within the forthcoming Space Station Freedom.
TL;DR: In this article, a simulation and direct observation of Marangoni convection in the half-zone system were carried out for two different cases, in the first case the surface of the melt zone was completely free, while in the second it was mostly in contact with a quartz ring.
TL;DR: In this article, a three dimensional thermocapillary convection in a cubical cavity is considered and a consistent finite differencing procedure which enables this integral constraint to be satisfied to machine accuracy is outlined.
TL;DR: In this article, an asymptotic model for the nonsteady, nonplanar deflagration of energetic solids, such as nitramines, that experience exothermic reactions in liquid layers at their surfaces is derived.
TL;DR: In this paper, the authors used non-linear equations describing finite-amplitude deformation of the interfaces /1/ of a system of horizontal immiscible liquid layers, long-wave convective flows are studied for nearly critical Marangoni numbers.
TL;DR: In this paper, the coupling of the Marangoni and capillary instabilities in an annular thread of liquid heated along its axis was shown to give rise to traveling waves, and it was also shown that coupling of both instabilities is not able to stabilize capillary breakup.
TL;DR: In this paper, the presence of a precursor film in front of the spreading macroscopic film, whether it is by prewetting the substrate or by surface diffusion or multilayer absorption, can prevent the development of the fingering instability.
Abstract: Recent experimental and theoretical efforts have revealed the existence of a fingering instability at the moving front of thin liquid films forced to spread under gravitational, rotational or surface shear stresses, as for example by using the Marangoni effect. The authors describe how the presence of a precursor film in front of the spreading macroscopic film, whether it is by prewetting the substrate or by surface diffusion or multilayer absorption, can prevent the development of the instability.
TL;DR: In this paper, an intricate flow pattern with azimuthal symmetry was observed through the use of schlieren photography, which was characterized in terms of its qualitative features and the region of concentrations for which it occurred.
Abstract: When a drop of one ethanol-water solution is placed on the surface of a different ethanol-water solution, the difference in surface tension along the drop boundary causes spreading behavior which depends sensitively on the ethanol concentrations of the two bulk phases. Within a narrow range of concentration combinations, an intricate flow pattern with azimuthal symmetry was observed through the use of schlieren photography. This phenomenon, believed to be a novel Maragoni effect, was characterized in terms of its qualitative features and the region of concentrations for which it occurred. The concentration zone was consistent with a fixed surface tension difference between the two solutions.
01 Jan 1990
TL;DR: In this article, a thermal buoyancy and surface tension driven convection is numerically investigated in a system with two, immiscible fluids, where the upper fluid meniscus and the interface are assumed to be flat and undeformable in the calculations.
Abstract: Thermal buoyancy and surface tension driven convection is numerically investigated in a system with two, immiscible fluids. The geometry investigated, has an open cavity configuration with the lighter fluid situated on top of the heavier fluid, forming a stable layered system. The upper fluid meniscus and the interface are assumed to be flat and undeformable in the calculations. The governing equations and boundary/interface conditions are solved by a control volume based finite difference scheme for two pairs of immiscible fluids; the water-hexadecane system and a so called generic system. The steady state calculations show, that dramatically different flows are predicted when the interfacial tension effects are included or excluded from the system model. These differences are particularly appreciable in surface tension dominated flows, that are typical of microgravity situations. Complex flow patterns, with induced secondary flows are noticed in both the fluids. In general, the overall system heat transfer is found to increase with increases in the thermal buoyancy and surface tension effects, but the behavior of the system flow and thermal fields is not easy to characterize, when different combinations of these forces are considered.
TL;DR: In this paper, the dopant distribution from different levels of Marangoni flows were analyzed in a modified Bridgman configuration with partially free surfaces during the flight of the rocket MASER 2.
TL;DR: In this article, the spatial distribution of impurities and structural defects of Te- and Si-doped GaAs grown in space have been investigated using capacitancevoltage (C-V ) method and scanning photoluminescence (SPL) and cathodolumininescence image (CLI) techniques.
TL;DR: In this paper, the problem of surface tension driven instability in a rotating spherical fluid shell is studied. But the authors assume that the fluid layer is Boussinesq-like, heated from the inner sphere and placed in a microgravity environment (Marangoni problem).
Abstract: New results concerning the problem of surface‐tension‐driven instability in a rotating spherical fluid shell are presented. The fluid layer is assumed to be Boussinesq‐like, heated from the inner sphere and placed in a microgravity environment (Marangoni problem). Small‐amplitude disturbances are considered and the normal mode problem is solved numerically by means of a finite difference technique. Marginal stability curves are computed and surstability is exhibited. Onset of convection is subordinated to several parameters like the thickness of the layer, its angular velocity, and its viscous and diffusive properties; all these effects receive a special treatment.
TL;DR: In this article, the onset of motion in two immiscible fluids heated from below by a uniform heat flux is studied analytically, and the critical Rayleigh and Marangoni numbers are determined.
Abstract: The onset of motion in two immiscible fluids heated from below by a uniform heat flux is studied analytically. The solution is based on the parallel-flow assumption. The critical Rayleigh and Marangoni numbers are determined. The superimposed cell mode in a single fluid layer is found to be possible when Ma is greater than 180. The secondary cell in the two-layer system can only appear in one of the layers, and the conditions leading to the secondary cell are specified. The influence of upper free boundary, responses in a solid-layer and a fluid-layer system, as well as the use of equivalent Rayleigh numbers are also discussed. 19 refs.
TL;DR: In this paper, the linear stability of the time-dependent, spherically-symmetric concentration profiles in a motionless liquid was studied. But the authors only considered the case of neutral stability and showed that the stability properties are strongly dependent on the curvature of the interface and on the mass transfer Biot number.
Abstract: A liquid layer containing a single solute is bounded on the outside by a rigid spherical surface and on the inside by a concentric gas/liquid interface. The solute evaporates from the liquid to the gas phase and, if the surface tension depends on the solute concentration, surface-tension driven convective flows may arise (Marangoni instability). Assuming zero-gravity conditions and using a normal-mode approach, we study the linear stability of the time-dependent, spherically-symmetric concentration profiles in a motionless liquid. Numerical results are presented for Marangoni numbers and perturbation wave numbers in the case of neutral stability. It turns out that the system's stability properties are strongly dependent on the curvature of the interface and on the mass-transfer Biot number.