Exploring droplet impact near a millimetre-sized hole: comparing a closed pit with an open-ended pore

We investigate drop impact dynamics near both closed pits and open- ended pores experimentally. The resulting impact phenomena differ greatly for a pit or a pore. For the first, we observe three phenomena: a splash, a jet and an air bubble, whose appearance depends on the distance between impact location and pit. Furthermore, we found that splash velocities can reach up to seven times the impact velocity. Drop impact near a pore, however, results solely in splashing. Surprisingly, two distinct and disconnected splashing regimes occur, with a region of plain spreading in-between. For pores, splashes are less pronounced than in the pit case. We state that, for the pit case, the presence of air inside the pit plays a crucial role: it promotes splashing and allows for air bubbles to appear.Comment: 17 pages, 11 figures, 1 supplementary movie, submitted to JF

Rodless Weissenberg effect

The climbing effect of a viscoelastic fluid when stirred by a spinning rod is well documented and known as Weissenberg effect(Wei et al, 2006). This phenomenon is related to the elasticity of the fluid. We have observed that this effect can appear when the fluid is stirred without a rod. In this work, a comparison of the flow around a spinning disk for a Newtonian and a non-Newtonian liquids is presented. The flow is visualized with ink and small bubbles as fluid path tracers. For a Newtonian fluid, at the center of the spinning disk, the fluid velocity is directed towards the disk (sink flow); on the other hand, for a viscoelatic liquid, a source flow is observed since the fluid emerges from the disk. The toroidal vortices that appear on top of the disk rotate in opposite directions for the Newtonian and non-Newtonian cases. Similar observations have been reported for the classical rod climbing flow (Siginer, 1984 and Escudier, 1984). Some authors have suggested that this flow configuration can be used to determine the elastic properties of the liquid (Escuider, 1984 and Joshep, 1973)

Some Topics on the Physics of Bubble Dynamics in Beer

Besides being the favorite beverage of a large percentage of the population, a glass or bottle of beer is a test bench for a myriad of phenomena involving mass transfer, bubble-laden flows, natural convection, and many more topics of interest in Physical Chemistry. This paper summarizes some representative physical problems related to bubbles that occur in beer containers, pointing out their practical importance for the industry of beverage processing, as well as their potential connection to other processes occurring in natural sciences. More specifically, this paper describes the physics behind the sudden foam explosion occurring after a beer bottled is tapped on its mouth, gushing, buoyancy-induced motions in beer glasses, and bubble growth in stout beers

Transition to convection in single bubble diffusive growth

We investigate the growth of gas bubbles in a water solution at rest with a supersaturation level that is generally associated with diffusive mass transfer. For CO 2 bubbles, it has been previously observed that, after some time of growing in a diffusive regime, a density-driven convective flow enhances the mass transfer rate into the bubble. This is due to the lower density of the gas-depleted liquid which surrounds the bubble. In this work, we report on experiments with different supersaturation values, measuring the time t conv it takes for convection to dominate over the diffusion-driven growth. We demonstrate that by considering buoyancy and drag forces on the depleted liquid around the bubble, we can satisfactorily predict the transition time. In fact, our analysis shows that this onset does not only depend on the supersaturation, but also on the absolute pressure, which we corroborate in experiments. Subsequently, we study how the depletion caused by the growth of successive single bubbles influences the onset of convection. Finally, we study the convection onset around diffusively growing nitrogen N 2 bubbles. As N 2 is much less soluble in water, the growth takes much longer. However, after waiting long enough and consistent with our theory, convection still occurs as for any gas-liquid combination, provided that the density of the solution sufficiently changes with the gas concentration

Growing bubbles in a slightly supersaturated liquid solution

We have designed and constructed an experimental system to study gas bubble growth in slightly supersaturated liquids. This is achieved by working with carbon dioxide dissolved in water, pressurized at a maximum of 1MPa and applying a small pressure drop from saturation conditions. Bubbles grow from hydrophobic cavities etched on silicon wafers, which allows us to control their number and position. Hence, the experiment can be used to investigate the interaction among bubbles growing in close proximity when the main mass transfer mechanism is diffusion and there is a limited availability of the dissolved specie