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Dynamics of Shape Oscillations of a Bubble Attached to a Capillary Tip
Vobecká, Lucie ; Vejražka, Jiří ; Orvalho, Sandra ; Zedníková, Mária ; Tihon, Jaroslav
The shape oscillations of a bubble, which is attached to a tip of a capillary tube, are studied experimentally. It is observed that the attachment leads to an appearance of an additional low-frequency mode (denoted as mode 1), when compared to standard theories of oscillations of free bubbles or drops. It is observed that the frequency of mode 1 scales with the bubble size as f ~ D^(-2). The oscillation dynamics of a bubble is strongly influenced if some surface active agent is present in the liquid. Due to interfacial elasticity, the surfactants presence in low concentration increases the oscillation frequency. The decay of oscillations is also faster, probably due to an increase of energy dissipation by Marangoni stresses.
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Research of Multiphase Systems at ICPF AS CR Prague
Zedníková, Mária ; Růžička, Marek ; Drahoš, Jiří
The aim of this contribution is to present to the Czech waste water treatment community the multiphase flow research at the ICPF ASCR. The goal of the research is to understand the basic physical mechanisms of flow systems with two or more phases. The interest covers a broad range of the multiphase flow systems; for instance: production and hydrodynamics of bubbly mixtures, flow regimes and their identification, effect of control parameters on the flow regimes, mass transfer in gas-liquid systems, bubble formation, coalescence and break-up, hydrodynamic interactions of bubbles, interaction of bubbles with solid particles, sedimentation of polydisperse mixtures etc.
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Pohyb kulové bubliny v okolí padající kulové částice
Vejražka, Jiří
This report focuses on a motion of a small spherical bubble, which rises in a still liquid particle and encounters a falling spherical particle. We consider the case of very small bubbles and of relatively large particle (whose size is much bigger compared to the bubble). The report provides expressions for forces acting on the bubble and equations for the bubble motion. The motion equations form a system of ordinary differential equations, which should be solved numerically. The purpose of this study is to provide a mathematical model, which would describe experimental observations by Hubička et al. (2009). In these experiments, a decrease of collision efficiency of the flotation process is observed if the particle is moving, compared to the case of still particle.
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Vliv viskoelastických vlastností mezifázového rozhraní na oscilace bubliny
Vejražka, Jiří ; Vobecká, Lucie ; Zedníková, Mária ; Orvalho, Sandra ; Tihon, Jaroslav
Shape oscillations of bubbles in surfactant solutions are investigated by means of high-speed imaging. Two cases are studied: bubbles attached to a capillary tip, and bubbles freely rising after detachment. The frequency f and the decay time τ of shape oscillations are evaluated, and their dependence on the surfactant concentration and on the bubble size is investigated. If the surfactant is present, τ shortens and a minimum is found for a certain concentration. This observation demonstrates that in the surfactant solutions, the energy dissipation linked to interfacial effects can be much more important than the dissipation due to liquid viscosity. The frequency f increases with increasing concentration of the surfactant first, and then it drops rapidly at concentration, at which τ is minimal. The initial increase of the oscillation frequency suggests that the interfacial elasticity can play an important role in surfactant solutions.
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Hydrodynamika bubliny narážející na stěnu. Experiment a modelování
Zedníková, Mária ; Vejražka, Jiří ; Růžička, Marek ; Drahoš, Jiří
The contribution deals with both experimental and theoretical investigation of collision of a bubble with a horizontal hydrophobic (glass) surface. The terminal bubble velocity, impact velocity, contact time of bubble with the wall and restitution coefficient (ratio of restitution and terminal velocity) are evaluated (by means of a high-speed camera) as a function of bubble size, which is ranging from 0.34 to 2.07 mm. The experimental results are compared with the models based on a balance of forces acting on a bubble during the interaction process. A good agreement is showed between the experimental data and theoretical predictions.
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