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Influence of a coaxial gas flow on the evolution of oscillatory states in a liquid bridge

par Yasnou, Viktar ;Gaponenko, Yuri ;Mialdun, Aliaksndr ;Shevtsova, Valentina
Référence International Journal of Heat and Mass Transfer, 123, page (747-759)
Publication Publié, 2018-08

Article révisé par les pairs

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Résumé :

We present an experimental and complementary computational study of a two-phase flow in a liquid bridge that develops under the action of buoyant and Marangoni forces in the presence of a gas stream parallel to the interface. The gas flow is counter-directed with respect to the steady flow in liquid. The forced gas flow along the interface provides actions on the system via shear stresses and heat exchange. For the experimental fluids (n-decane, nitrogen) the ratio of viscosities is large, about 40, and the gas Reynolds number is moderate, Reg = 120. Thus, heat transfer is the prevailing mechanism by which gas affects the flow in a liquid. The effect of gas temperature on the evolution of flow states is examined. The study reveals that in the supercritical region, ΔT>1.25ΔTcr, the flow dynamics can be divided in three regimes relative to the gas temperature. When the gas is colder than the temperature of the supporting disk, multiple transitions between the oscillatory states occur: periodic, quasi-periodic with two frequencies, quasi-periodic with three frequencies and noisy quasi-periodic with three frequencies. In the case, when the gas temperature approaches the temperature of the cold disk and goes up to the mean temperature, the flow remains periodic up to the largest tested ΔT. In the case of hotter gas, the flow also remains periodic far above the threshold of hydrothermal instability, but the azimuthal mode of the periodic oscillatory flow is changed. The stability window is found to exist between these two azimuthal modes and its location is sensitive to the gas parameters as well as to the geometry of a liquid bridge. It opens a possibility that oscillatory instability can be stabilized by choosing specific temperatures and velocities of counter-current gas.