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Mechanics
Thin liquid films lie in a focus of numerous theoretical and experimental studies. The reason for the growing interest in this subject is the abundance of technological applications of the thin films. The dynamics of films on heated substrates is generally governed by gravity, surface tension, thermocapillarity etc. The interaction of these forces often results in complex nonlinear behavior exhibited by the films. The liquid films on heated walls are subject to various modes of thermocapillary instability, which arises in the films as a result of temperature variation along the gas-liquid interface [1], for example the long-wave thermocapillary instability, which is one of the major reasons of the film rupture [1]-[2]. Thermocapillarity-induced flow and evolution of a thin liquid film on horizontal structured heated walls are studied theoretically and numerically.The thickness of film over topography is always non-uniform. As a result, the temperature at the liquid-gas interface is also inhomogeneous, even if the wall is isothermal. Thermocapillary stresses arise due to the temperature non-uniformity and bring the liquid into motion. The liquid in the vicinity of the interface flows towards the locations of higher surface tension (or lower temperature). The steady deformation of the liquid-gas interface and the vortex flow pattern within the film are predicted for the steady continuous films in the case of the grooved walls. It has been recently shown that the structured surfaces significantly affect the stability characteristics of isothermal falling films [3].
In this work the dynamics of nonisothermal liquid film evolution towards the moment before the rupture on the grooved substrate is simulated numerically in the framework of the long-wave theory. It is found that the structured walls destabilize the films, so that the disturbance growth rate increases with increasing the groove amplitude. The wall structure strongly affects the film evolution. The rupture time significantly decreases on structured walls. The film pattern at the moment before the rupture is affected by the wall topography. Grooved walls promote the formation of rivulets, which are advantageous for the heat transfer enhancement.
This work has been supported by the Russian Foundation for Basic Research (project 04-01-00355) and Council for the Russian Federation Leading Scientific Schools Support (Grant No NSh-902.2003.1).
References
[1] Davis, S. H., Thermocapillary instabilities, Annu. Rev. Fluid Mech., 19 (1987), 403-435.
[2] Oron, A., Nonlinear dynamics of three-dimensional long-wave Marangoni instability in thin liquid films, Physics of Fluids, 12 (2000),1633-1645
[3] Gambaryan-Roisman, T., Stephan, P., Analysis of falling film Evaporation on Grooved Surfaces, J. Enhanced Heat Transfer, 10 (2003), 369-381.
Note. Abstracts are published in author's edition
Last update: 06-Jul-2012 (11:52:45)