Showing papers on "Marangoni effect published in 1984"

High Marangoni number convection in a square cavity

Abstract: Steady thermocapillary flow is examined in a square two‐dimensional cavity with a single free surface and differentially heated side walls. The numerical solutions are obtained with a finite difference method applied to a streamfunction‐temperature formulation. This work investigates the Prandtl number dependence, structure, and stability of high Marangoni number flow. It is found that the character of thermocapillary flow is highly sensitive to the value of the Prandtl number over a range of Marangoni numbers exceeding 1×105 for 1≤Pr≤50, the magnitude of the flow showing nonmonotonic dependence on the Marangoni number for Pr≤∼10. A complete structural analogy is observed between flow in a cavity driven by a moving lid and thermocapillary flow in the boundary layer limit, and it is found that all the solutions, spanning a wide range of Marangoni and Prandtl numbers, are linearly stable to a restricted class of disturbances.

A nonlinear stability analysis of the Bénard–Marangoni problem

Abstract: A nonlinear analysis of Benard–Marangoni convection in a horizontal fluid layer of infinite extent is proposed. The nonlinear equations describing the fields of temperature and velocity are solved by using the Gorkov–Malkus–Veronis technique, which consists of developing the steady solution in terms of a small parameter measuring the deviation from the marginal state. This work generalizes an earlier paper by Schluter, Lortz & Busse wherein only buoyancy-driven instabilities were handled. In the present work both buoyancy and temperature-dependent surface-tension effects are considered. The band of allowed steady states of convection near the onset of convection is determined as a function of the Marangoni number and the wavenumber. The influence of various dimensionless quantities like Rayleigh, Prandtl and Biot numbers is examined. Supercritical as well as subcritical zones of instability are displayed. It is found that hexagons are allowable flow patterns.

The contribution of chemistry to new Marangoni mass-transfer instabilities at the oil/water interface

Abstract: Spontaneous interfacial motions appear at an interface between two immiscible phases in a state far from equilibrium, e.g. an aqueous phase of an organic acid or a complex ion and an organic phase of a long-chain surfactant molecule. The instabilities observed are related to variations in the interfacial tension. It is shown that they resemble the well known Marangoni effect by considering interfacial convection and the coupling between diffusion and convection fluxes, but they differ by the presence of chemical reactions. The notion of assisted desorption is defined in order to interpret the experiments.The analysis of this phenomenon could be useful in determining the optimal conditions for obtaining convective interfacial transfer to enhance liquid–liquid extraction processes.

Free Liquid Surface Response Induced by Fluctuations of Thermal Marangoni Convection

Abstract: The original enthusiasm for processing in a microgravity environment has been slightly dimmed by the fact that liquid bridges are susceptible to surface oscillations and Marangoni convection. It has now been found that time fluctuations in the temperature gradient induce free liquid surface oscillations, which lead to large amplitudes in the vicinity of the resonances and possibly to the disintegration of the liquid system. An analytical solution leading to the magnification functions and phases of velocity, pressure distribution, and surface elevation is presented for an arbitrary axially periodic temperature field. Nomenclature a = radius of liquid column f(z) = function of angular coordinate z (/' = d//dz) /o, 77 = modified Bessel function of zeroth and first order and first kind, respectively p = liquid pressure r,

Marangoni waves induced by a multistable chemical reaction on thin liquid films

Abstract: It is shown that when steady states of a multistable kinetic system are attained at the extreme ends on the free surface of a thin liquid film, a simultaneous chemical and hydrodynamic wave can propagate with a constant velocity in the direction of the preferable concentration plateau. By using a systematic long-wave analysis, it is demonstrated that the surface deformation can cause thinning of the film when the wave propagates in the direction of the higher concentration region, while the film can swell when the wave moves in the opposite direction. The analysis, based on the presence of a long lateral diffusional scale compared with the film thickness, fails when the reaction scheme and the induced fluid motion act as to arrest the wave and reduce its velocity almost to a complete halt. Under such conditions, the separation of the scales is invalidated by developing shocks with steep local gradients which can result in a forward-breaking wave or film rupture.

Marangoni convection in space microgravity environments

Abstract: Thermally induced surface-driven convection (thermal Marangoni convection) was investigated in the Spacelab 1 microgravity environment The configuration studied is related to the floating-zone tec

Interfacial turbulence during the physical absorption of carbon dioxide into non-aqueous solvents

Abstract: Interfacial turbulence during the physical absorption of CO2 into non-aqueous solvents such as methanol and toluene was investigated experimentally from the point of view of the mass transfer rates. Liquid-phase mass transfer coefficients were measured in the range of gas-liquid contact time t = 0.1-1000 s, using a wetted-wall column, a two-dimensional source flow cell and a quiescent liquid cell, and were compared with calculated values from the penetration theory. The gas-liquid interface during absorption was observed by schlieren photography. It was found that interfacial turbulence owing to the Marangoni effect occurs around t = 0.1 s and succeedingly a density driven convection is superimposed on the turbulence after t = 5-50 s when CO2 is absorbed into non-aqueous (organic) solvents. It is also found that Marangoni-type turbulence occurs in the condition of negative Marangoni number.

Marangoni effect in the water wetting of surfactant coated human hair fibers

Abstract: Wetting force curves have been obtained, using a technique based on the Wilhelmy principle, for individual human hair fibers treated with a cationic surfactant (stearyldimethylbenzylammonium chloride). The characteristic stick-slip nature of these curves has been attributed to desorption of the surfactant from the fiber surface into the wetting liquid at the contact line. Differences in surfactant concentration between the vicinity of the contact line and the bulk liquid give rise to surface tension gradient related flows in the film near the contact line, which result in apparent changes in contact angle and wetting force. Such surface flows originating from surface tension gradients are known as Marangoni effects. An apparent increase in contact angle and reduction in wetting force in the dynamic Wilhelmy measurement seem to result when the surface tension of the liquid at the contact line is lower than that of the bulk liquid, giving rise to a surface tension gradient. An instantaneous decrease in contact angle and increase in wetting force seems to be due to the jumping of the meniscus when the surface tension gradient is reduced by the diffusion of the surfactant into the bulk liquid. The amplitude and frequency of the stick-slip depends on the distribution of the surfactant and the nature of its binding to the fiber surface, respectively.

Marangoni and electric field effects upon mass transfer to translating drops

Abstract: Interfacial stresses arising from the transfer of an interfacial tension-lowering solute (Marangoni effects) or the presence of an electric field may significantly alter the interfacial velocity of...

The effect of evaporative vapor recoil on the instability of liquid jets

Abstract: The stability of cylindrical liquid jets undergoing evaporation is examined theoretically with a linear analysis. Prediction of the effects on jet length of Marangoni flow and the vapor recoil force exerted on the liquid surface by evaporating molecules is obtained for a laminar viscous jet in inviscid surroundings. These predictions indicate that evaporation may have an important stabilizing influence which markedly elongates the jet. Under similar circumstances, the size or the resulting drops is predicted to be significantly reduced.