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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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Transportní charakteristiky různých vícemíchadlových konfigurací v míchané disperzi kapalina-plyn s vyšší viskositou
Moucha, T. ; Zedníková, Mária ; Linek, V.
Mixing intensity, gas hold-up and volumetric mass transfer coefficient of various multiple-impeller configurations are measured in a vessel of inner diameter 0.29 m equipped with three impellers on a common shaft. Five types of impellers are used. Distilled water with 3 vol.% Sokrat 44 is used as a liquid phase with Newtonian behaviour and viscosity 12.9 mPa.s. Air is used as gas phase. Mixing intensity was measured using tracer experiment and Dynamic Pressure Method was used for the measurement of volumetric mass transfer coefficient. Transport characteristics are presented for individual impeller configurations as functions of power consumption and superficial gas velocity. The impellers are compared each other and with transport characteristics for non-viscous solutions measured previously.
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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 0.4 to 1.1 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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Bubble Production Controlled by Needle Movement
Vejražka, Jiří ; Stanovský, Petr ; Zedníková, Mária
For the research of multiphase flows, it is often needed to produce bubbles of well-defined size. Examples of such a research are studies of bubble acoustic emission, bubble interactions with solid particles (e.g. in flotation process) or interactions between bubbles. To produce a well-defined bubble is, however, rather difficult, and it is even more difficult to vary the bubble size between different experimental runs. For this reason, we have produces an instrument ("bubble generator", which produces bubbles in a controlled manner, enableng to set indepedently the bubble size, bubbling frequency and total number of bubbles. The bubbling control is achieved by moving the needle, on which the bubbles are produced.
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Experimental Study of Bubble Interactions with Wall.
Zedníková, Mária ; Vejražka, Jiří ; Růžička, Marek
The work deals with the experimental study of hydrodynamic behaviour of bubbles with various sizes bouncing on a wall in liquid. The aim of the work is to obtain bubble trajectory and bubble velocity. The experiments are made using a high speed camera Kodak Ektapro (max 10 000 fps). From the images, the bubble diameter, its centre, steady-state bubble rise velocity and also local velocity especially during the bouncing. The rebounding conditions are also evaluated. The results are compared with the models available in the literature.
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Spontaneous Bubble Production on the Needle
Vejražka, Jiří ; Zedníková, Mária ; Stanovský, Petr
The study of spontaneous bubble production on the needle is necessary to understand all possibilities to control the bubble production on the needle with desired volume and desired production frequency. For this reason the system, where the gas flows into the chamber and continues through the needle, is studied. This system is modeled using modified model of Oguze and Prosperetti (1993). The model results enable to understand how the chamber volume, the diameter and the length of the needle influence the forming process and size of the bubbles. The experimental results are also presented.
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Controlled Production of Bubbles
Vejražka, Jiří ; Stanovský, Petr ; Zedníková, Mária
Two apparatuses for the producing of bubbles with desired volume V and production frequency f are designed. In the first one, the bubble formation is controlled by needle movement and in the second one by changing the chamber volume. Production of bubbles in both devices is modeled using simple model enabling to estimate the range of bubble volumes V and frequencies f, for which the devices will work properly.
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