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Vliv pulzací nátoku na strukturu toku v kanále za náhlým rozšířením.
Pěnkavová, Věra ; Tihon, Jaroslav
The wall shear rate profiles were measured along the bottom and roof walls of rectangular channel with backward-facing step. The profiles were measured by two-strip electrodiffusion probes. It is possible to see the strong effect of the inlet flow pulsations on the flow structure. The influence of the inlet flow pulsation was studied for various frequence and amplitude for water when the Reynolds number was ranging from 100 to 1500 and expansion ratio of the channel was 2.
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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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Měření přestupu tepla a frekvence oscilací s fluidickým generátorem syntetizovaného impaktního proudu
Tesař, Václav ; Trávníček, Zdeněk ; Kordík, Jozef ; Randa, Zdeněk
The paper discusses recent results of an experimental research of annular impinging hybrid-synthetic jets generated by a no-moving-part fluidic actuator. The actuator is based on a new principle and the first part of the paper discusses the basic configuration idea and the relationship with earlier hybrid-synthetic jet generators. The next part of the paper provides information of a strange phenomenon – an unexpected high-temperature region found on the impingement surface. Also discussed are the measurements of the oscillation frequency. The most important result is the substantial increase of heat transfer efficiency compared with the steady flow from the same nozzles.
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Fyzikální modelování srdečně cévní soustavy na ÚT AVČR
Pražák, Josef
The physical modeling remains an important tool for theoretical and practical studies of CVS. Nowadays, the most important applications of physical modeling of CVS are the testing and developing of artificial substitutions of CVS elements and the application of it as a counterpart for mathematical models. On the IT, the physical modeling of the CVS flow phenomena is developed since the last century (more then six years) in the Laboratory of biomechanics. In its contemporary state, the IT physical model of CVS represents a universal system (construction kit) suitable for a large class of applications.
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