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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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Gas Hold-up and Volumetric Mass Transfer Coefficient of Various Impeller Types in Gas-Liquid Dispersion with Higher Viscosity
Zedníková, Mária ; Linek, V. ; Moucha, T.
In a vessel with inner diameter 0.29 m supplied by one, two or three impellers on a common shaft, there were measured transport characteristics (gas hold-up and volumetric mass transfer coefficient) in dependence on power consumption. As an impeller there was used the pitched blade impeller pumping the liquid either upwards or downwards. Air was used as a gas phase and 3% solution of Sokrat 44 as a liquid phase. The solution behaves as a newton liquid with viscosity 12.9mPa.s. Volumetric mass transfer coefficient was measured by dynamic pressure method. Gas hold-up and kLa were presented in dependence on power consumption and on gas superficial velocity. Results are compared with the data of given impeller types obtained in low viscous solutions and with the data of other impeller types.
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