Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session L9: Interfacial/Thin Film Instability V: Evaporation |
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Chair: Omar Matar, Imperial College London Room: 25B |
Monday, November 19, 2012 3:35PM - 3:48PM |
L9.00001: Stability of evaporating liquid layer with insoluble surfactant Alexander Mikishev, Alexander Nepomnyashchy A horizontally infinite layer of incompressible Newtonian liquid with insoluble surfactant on the deformable surface is considered. The evaporation process is described by 2D one-side model. Therefore, the assumptions of small density, small viscosity and small thermal conductivity of the gaseous phase compared to the same properties of the liquid phase are accepted. Surface tension of the liquid-vapor surface linearly depends on temperature and concentration of surfactant. Using the long-wave approximation and assumption of slow time evolution the system of nonlinear equations is obtained. That system describes the spatiotemporal behavior of the layer interface and the field of the surfactant concentration. The equations retain all relevant physical effects which take place in the system. Linear stability analysis of the base state in the case of quasi-equilibrium evaporation, when the interfacial temperature equals the saturation one, is performed. [Preview Abstract] |
Monday, November 19, 2012 3:48PM - 4:01PM |
L9.00002: Influence of evaporation on a thin binary liquid film flowing down a heated inclined plate Juthamas Kamrak, Benoit Scheid, Pierre Colinet We investigate the evolution of a two-component liquid film (here consisting of glycerine in water) falling down a heated plate, while water evaporates (glycerine is assumed to be non-volatile). The liquid phase is separated from pure water vapour by a deformable interface. We study the influence of both heat and mass transfer on the evolution of the liquid film. The temperature and concentration variations due to the evaporation of the solvent induce thermal and solutal Marangoni stresses on the free surface, thus affecting the evolution of the film. The mathematical model is developed by combining the lubrication theory with a weighted residuals approach. We obtain a set of coupled equations for the evolution of the film thickness, the velocity, the temperature and the concentration fields, at first-order. Stationary solutions are then calculated for different control parameters and show an intricate dependence of the different variables in the transition region where the evaporation flux reaches its maximum. [Preview Abstract] |
Monday, November 19, 2012 4:01PM - 4:14PM |
L9.00003: Solutal Marangoni instability in a binary liquid layer evaporating into air: the importance of transients in the gas for highly unstable cases Hatim Machrafi, Alexey Rednikov, Pierre Colinet, Pierre Dauby This study considers an evaporating horizontal binary-liquid layer (aqueous solution of ethanol; mass fraction 0.1) in contact with air with an imposed transfer distance. Fully transient and horizontally homogeneous solutions for the reference state are first calculated. Then, the linear stability of these solutions is studied using the frozen-time approach. Solutal and thermal Rayleigh-B\'{e}nard-Marangoni instabilities are taken into account together with the Soret effect, although the solutal Marangoni mechanism appeared to be the most important one. Considering several gas-to-liquid thickness ratios ($H)$, we calculate the critical times for the instability onset in a liquid layer of a given thickness. We also uncover the minimum liquid thicknesses under which no instability can ever occur. We subsequently observe that two distinctly different types of minimum thicknesses exist depending on $H$, examining each one of them. Then a closed-form analysis of the instability at small times has been developed. Finally, it has also been observed that, regardless of the gas-to-liquid thickness ratio, an asymptotic value of the critical time exists as the liquid layer increases, this critical time being approximately 1 $\mu $s. [Preview Abstract] |
Monday, November 19, 2012 4:14PM - 4:27PM |
L9.00004: Experimental studies of a volatile simple fluid subject to a horizontal temperature gradient Yaofa Li, Benjamin Chan, Minami Yoda Our fundamental understanding of transport in a nonisothermal liquid layer in the presence of evaporation and condensation is limited. Particle-image velocimetry (PIV) was used to measure 2D-2C liquid-phase velocity fields in layers of water and low-viscosity volatile silicone oil with an average depth of a few mm subject to a temperature difference of about 10\r{ }C over a horizontal distance of $\sim $5~cm. Two-color laser-induced fluorescence was also used to measure liquid-phase temperature fields in water. The liquid layers, which were confined in a 1~cm deep rectangular test cell, were studied under both ambient air and in equilibrium with their vapor. Given that thermocapillarity due to the changes in temperature associated with phase change at the free surface can be significant in these flows, results for water, and water with surfactant concentrations below and above the critical micellar concentration are compared. The experimental data for both fluids are also compared with numerical simulations. [Preview Abstract] |
Monday, November 19, 2012 4:27PM - 4:40PM |
L9.00005: Numerical studies of a volatile simple fluid subject to a horizontal temperature gradient Tongran Qin, Roman Grigoriev Rayleigh-B\'enard and Marangoni convection in a layer of a homogeneous fluid with a free surface in the absence of phase change is a classic--and extensively studied--problem of fluid mechanics. The balance between the buoyancy and thermocapilly forces, however, depends, in a rather delicate manner, on the conditions of the experiment. Phase change, in particular, has a major effect on convection. Significant latent heat absorbed or released at the free surface as a result of evaporation or condensation can dramatically alter the interfacial temperature, and hence, thermocapillary stresses. This talk will use numerical simulations to illustrate how the phase change rates and the interfacial temperature distribution depend on two key factors: the accommodation coefficient of the working fluid and the presence of non-condensable gases, such as air. We will also compare numerical results with experiments. [Preview Abstract] |
Monday, November 19, 2012 4:40PM - 4:53PM |
L9.00006: Experimental studies of volatile binary fluids subject to a horizontal temperature gradient Minami Yoda, Yaofa Li, Benjamin Chan Convection in a binary fluid with a free surface in the presence of evaporation and condensation is a complex and poorly understood problem. In a two-component fluid where one component is more volatile and has a lower surface tension $\sigma $ than the other, the surface tension of the mixture increases as temperature increases due to solutocapillary effects. In contrast, $\sigma $ decreases as temperature increases in a simple fluid due to thermocapillary effects. The dynamics of the flow in $O$(1 mm) layers of dilute water-methanol mixtures driven by a temperature difference of about 10\r{ }C over a horizontal distance of $\sim $5~cm was studied using 2D-2C particle-image velocimetry (PIV). The liquid layers, which are confined in a 1~cm deep rectangular test cell, are studied under both ambient air and in equilibrium with their vapor(s). The experimental data for these binary fluids are compared with numerical simulations. [Preview Abstract] |
Monday, November 19, 2012 4:53PM - 5:06PM |
L9.00007: Numerical studies of a volatile binary fluid subject to a horizontal temperature gradient Roman Grigoriev, Tongran Qin Convection in a volatile binary fluid with a free surface is an extremely rich, and still a relatively poorly understood, problem. The richness comes from the interplay of three different forces: buoyancy, thermocapillarity, and solutocapillarity. While solutocapillarity is typically associated with the Soret effect, in the presence of phase change this force arises primarily as a result of differential evaporation (or condensation) of the two components of the binary mixture. In this talk we will discuss some interesting manifestations of solutocapillarity, such as the instability leading to the emergence of traveling waves analogous to hydrothermal waves is systems driven by thermocapillarity. Comparison of numerical results with experiments will also be provided. [Preview Abstract] |
Monday, November 19, 2012 5:06PM - 5:19PM |
L9.00008: On phase change in thermocapillary flows Pedro Saenz, Prashant Valluri, Khellil Sefiane, George Karapetsas, Omar Matar We present the findings from our 3D direct numerical study of thermocapillary flows undergoing phase change. A liquid-gas model with VOF interface-tracking technique is employed to investigate stable and unstable (hydrothermal waves) scenarios. The spatiotemporal evolution of the local evaporation flux is determined with the assumption that vapour phase just above interface is at a local thermodynamic equilibrium with the liquid phase below. The transient vapour distribution in the gas is also accounted for by means of the solution of an advection-diffusion equation. We calculate the resulting spatially non-uniform flux and illustrate its controlling mechanisms, which involve the Marangoni effect and non-uniform vapour-pressure distribution due to the externally-imposed thermal gradient. We also present the flux's non-linear evolution due to the transient liquid-level reduction and its stabilizing-destabilizing effect on the thermal and physical interface fluctuations. The oscillatory temperature- and vapour-fields in the gas, tightly coupled with advection rolls observed, are also shown. [Preview Abstract] |
Monday, November 19, 2012 5:19PM - 5:32PM |
L9.00009: Evaporative Instability in Binary Mixtures Ranga Narayanan, Erdem Uguz In this talk we depict the physics of evaporative convection for binary systems in the presence of surface tension gradient effects. Two results are of importance. The first is that a binary system, in the absence of gravity, can generate an instability only when heated from the vapor side. This is to be contrasted with the case of a single component where instability can occur only when heated from the liquid side. The second result is that a binary system, in the presence of gravity, will generate an instability when heated from either the vapor or the liquid side provided the heating is strong enough. In addition to these results we show the conditions at which interfacial patterns can occur. [Preview Abstract] |
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