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Theoretical Description of Motion of a Spherical Bubble in Neighbourhood of a Falling Particle
Basařová, P. ; Vejražka, Jiří ; Zedníková, Mária ; Hubička, M.
The aim of this work is to broaden the knowledge of the hydrodynamic interactions that occur between bubbles and solids of a comparable size. Focusing on collision processes between a single rising bubble with mobile surface and a larger falling solid spherical particle in stagnant liquid, the theoretical model describing the bubble trajectory is given here. The model is based on forces acting on the bubble and utilizes also equation for the bubble motion. The bubble is considered to be spherical and its motion is straight and rectilinear. The particle is spherical and moves vertically down with a steady velocity; the flow around the particle is axially symmetric.
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Experimental Study of Bubble Interactions with the Solid Surface
Zedníková, Mária ; Vobecká, Lucie ; Vejražka, Jiří ; Růžička, Marek
The experiments were carried out in a rectangular vessel equipped with a device generating the bubbles of defined size ranging from 0.4 to 2.0 mm (Vejrazka et al., 2008). Cleaned glass was used as a hydrophilic surface and polypropylene, polyethylene and Teflon were used as hydrophobic surfaces. Deionised water with addition of sodium dodecyl sulphate was used as liquid. The collision and attachment process was observed by means of high speed camera. The following quantities were evaluated from the image sequences: impact and rebound velocities of a bubble, maximal bubble deformation during the contact with the surface and the time required for three-phase contact line formation. The experimental results were compared with our previous investigations (Fujasova-Zednikova et al., 2009).
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Purification of Biogas by Means of Membranes
Poloncarzová, Magda ; Vejražka, Jiří ; Izák, Pavel
The aim of this work is to find a way to lower carbon dioxide concentration in biogas and to purify it from undesirable gases by means of membrane. Ideally only one or two steps should be used to make the technology feasible and profitable. Liquid membranes are used because of their high selectivity and good permeability. Successful biogas purification method would open new opportunities in ecological fuels, especially if the methane content in biogas reached more than 95%; biogas could then replace the natural gas. In this work, a new supported ionic liquid has been tested and the first results have been obtained. Sweeping gas permeation was performed with model mixture of CO2 and CH4 1:1.
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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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The Study of Interactions of Bubbles with Solid Surface. The Effect of Surfactant Concentration and Type of Solid Surface
Vobecká, Lucie ; Zedníková, Mária ; Vejražka, Jiří ; Růžička, Marek
This contribution deals with experimental study of interactions between a bubble and a solid horizontal surface. The influence of surfactant concentration in liquid and of material of the solid surface on the interaction is observed. It is observed that the material of solid surface has not significant influence on the hydrodynamics of impact of bubble on a wall. The impact velocity is not affected by surfactant presence because the liquid flow around the bubble moves adsorbed surfactants to rear of the bubble and the interface at top of the bubble stays mobile. The presence of surfactant has strong effect on the bubble rebound, as the rebound velocity and the maximal distance of bubble from the wall decreases with increasing surfactant concentration. No bubble rebound is observed at high concentration of surfactant.
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Experiments on Large Bubbles Rising in an Inclined Flat Channel
Tihon, Jaroslav ; Pěnkavová, Věra ; Vejražka, Jiří
The motion of single air bubbles in an inclined flat water channel is investigated experimentally. The electrodiffusion technique of near-wall flow diagnostics is applied to measure the wall shear stress distribution under large bubbles rising along the upper channel wall. The directionally sensitive, two-strip electrodiffusion probes are used to detect the location of flow reversal in a thin liquid film separating the moving bubble from the wall. The electrodiffusion measurements are synchronized with the visual observation of bubble movement done by a high-speed camera. The experiments are carried out for three different channel heights (1.5, 4, and 8 mm) and cover a wide range of channel inclination angles (from horizontal to vertical position). The experimental results on bubble motion characteristics obtained in stagnant and co-flowing liquid arrangements are confronted with the recent predictions and scaling provided by theoretical models.
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Střihové napětí na stěně pod velkou bublinou stoupající v nakloněném plochém kanále
Tihon, Jaroslav ; Pěnkavová, Věra ; Vejražka, Jiří
The motion of single air bubbles in an inclined flat water channel is investigated experimentally. The electrodiffusion technique of near-wall flow diagnostics is applied to measure the wall shear stress distribution under large bubbles rising along the upper channel wall. The electrodiffusion measurements are synchronized with the visual observation of bubble movement done by a high-speed camera. The analysis of video records provides information on the bubble shape and terminal velocity. The experiments are carried out for three different channel heights and cover a wide range of channel inclination angles (from horizontal to vertical position). The experimental results on bubble motion characteristics obtained in stagnant and upward-flowing liquid arrangements are confronted with the recent predictions and scaling provided by theoretical models.
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