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Počáteční chování bubliny páry v přehřáté kapalině
Vejražka, Jiří
The model is based on a simplified law for heat transfer of a growing and moving bubble and on solving the forces acting on this bubble. The model is represented by a system of ordinary differential equations and can be used until the time when bubbles start to wobble. An partially successful (but not convincing) attempt to validate this model by comparison with available experimental data was done. In most cases, the bubble behavior is controlled by a balance of the buoyancy with the added-mass force. In this aspect, the bubble behavior differs considerably from the case of constant-volume bubbles, for which the added-mass force is usually negligible. For the case of spherical bubbles, a simple analytical solutions are provided.
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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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Hydrodynamické interakce mezi bublinami stoupajícími v řadě
Stanovský, Petr ; Vejražka, Jiří ; Růžička, Marek ; Drahoš, Jiří
Knowledge about hydrodynamic interaction between bubbles are essential to uderstanding of bubbly flows behavior. The aim of this work is to check the existence of stable separation distance between bubbles experimentally. Air bubbles were produced in ultra-filtered water using a special device - the bubble generator. Pictures were taken with a digital SLR kamera. Bubbles were illuminated by the back light, using a light diffuser. Pictures were processed in MATLAB using the Image Processing Toolbox. Equivalent bubble radius, nonsphericity of bubbles, horizontal spacing and vertical displacement. was evaluated from processed pictures. Behavior of bubbles was compared with theoretical assumptions and models.
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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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