Stability of a liquid film on a surface with periodic array of gas-filled grooves

We develop a linear stability theory for a thin liquid film on a structured solid surface with periodic grooves filled by a gas. The main mechanism driving the instability is due to the London-van der Waals disjoining pressure. The grooves are shown to have a destabilizing effect on the film. The results of linear stability analysis are compared with numerical simulations based on the strongly nonlinear equation for film thickness. © Springer Science+Business Media B.V. 2011.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Gravity effect on the locally heated liquid film driven by gas flow in an inclined minichannel

Thin nonisothermal liquid film flowing under action of gravity force and co-current gas flow, which create the tangential force on the gas-liquid interface, in an inclined minichannel is considered. 3D time dependant mathematical model has been developed. Effects of surface tension, temperature dependent viscosity and thermocapillarity are taken into account. The effect of gravity as well as the effect of gas speed has been studied to define main features of the film dynamics. In calculations vector of gravitational acceleration is oriented along the flow and is equal to the normal Earth gravity and Lunar gravity. Our investigations have shown that gravity has a significant effect on the film deformations. At the lower gravity conditions 3D liquid film pattern changes noticeably in spanwise direction and a middle stream between two main lateral waves appears. Also speed of film deformation is higher and stabilization time is longer. Variation of gas Reynolds number from 543 to 2000 does not change noticeably film pattern at normal gravity. At lower gravity conditions increasing of gas Reynolds number decreases significantly the width of the thermocapillary deformations and leads to a film stabilization.En ligne: http://www.springerlink.com/content/q281764097634023/info:eu-repo/semantics/publishe

Interfacial Thermal Fluid Phenomena in Thin Liquid Films

Films are ubiquitous in nature and play an important role in our daily life. The paper focuses on the recent progress that has been achieved in the interfacial thermal fluid phenomena in thin liquid films and rivulets through conducting experiments and theory. Phase shift schlieren technique, fluorescence method and infrared thermography have been used. A spanwise regular structures formation was discovered for films falling down an inclined plate with a built-in local rectangular heater. If the heating is low enough, a stable 2D flow with a bump at the front edge of the heater is observed. For lager heat flux this primary flow becomes unstable, and the instability leads to another steady 3D flow, which looks like a regular structure with a periodically bent leading bump and an array of longitudinal rolls or rivulets descending from it downstream. The heat flux needed for the onset of instability grows almost linearly with the increase of Re number. Strong surface temperature gradients up to 10-15 K/mm, both in the streamwise and spanwise directions have been measured. For a wavy film it was found that heating may increase the wave amplitude because thermocapillary forces are directed from the valley to the crest of the wave. Thin and very thin (less than 10 μm) liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel are a promising candidate for the thermal management of advanced semiconductor devices in earth and space applications. Development of such technology requires significant advances in fundamental research, since the stability of joint flow of locally heated liquid film and gas is a rather complex problem. Experiments with water and FC-72 in flat channels (height 0.2-2 mm) have been conducted. Maps of flow regimes were plotted. It was found that stratified flow exists and stable in the channels with 0.2 mm height and 40 mm width. The critical heat flux for a shear driven film may be up to 10 times higher than that for a falling liquid film, and reaches 400 W/cm 2 in experiments with water at atmospheric pressure. Some experiments have been done during parabolic flight campaigns of the European Space Agency under microgravity conditions. It was found that decreasing of gravity leads to a flow destabilization.En ligne: http://multi-science.metapress.com/content/16g611834x8287g3/?p=09735401317e43da8298b5719ad000d3&pi=1SCOPUS: ar.jinfo:eu-repo/semantics/publishe