| Summary: | 碩士 === 國立中正大學 === 機械工程所 === 98 === The present study aims at investigating the passage of a drop at a plan liquid-liquid interface by using Two-color model based lattice Boltzmann method. The solutions include position of liquid-liquid interface and rise speed and shape of the drop for surface tension、viscosity ratios and buoyancy. The bubble rises slowly under the interface due to the interfacial resistance, and then the pressure gradient within the thin film acts to drain the thin film, until bubble crosses the liquid-liquid interface in the less viscous light phase that a rise speed increase. During the approach toward the interface, the bubble entrains a column of the heavy liquid through the interface. A ring dimpling develops at the drop back and form a neck, the drop remains coated with a thick layer of heavy liquid as it passes though the interface until neck break. The entrained column of heavy liquid broken into a sequence of smaller drops by a capillary (Rayleigh) instability with enough rise speed. In numerical results, simulations of the drop accelerate as they enter the lower-viscosity upper fluid and are extended (acceleration in a quasi-steady Stokes flow is permitted owing to a change in geometry, but does not contribute to the local force balance in the fluid). The drop decelerate as they enter a higher-viscosity upper fluid and develop a dimple or small cavity at the back of the drop.
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