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Nová laboratorní parní zkušební trať
Peukert, Pavel ; Hrubý, Jan
A novel laboratory steam test rig is being developed. It is intended primarily for the following purposes: i. development and testing of probes for sampling dry steam to determine heterogeneous nuclei in the steam, ii. study of liquid-vapor transport of admixtures in boiling, iii. study of heat transport in boiling and condensation processes, especially methods of heat transfer enhancement. The test rig allows accurate adjustment of the mass flow up to 0.25 kg per minute and adjustment of pressure up to 34 MPa and temperature up to 400°C. In the present stage, the pressure is limited to 4 MPa.
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Kapky v plynných proudech: jejich původ, měření a separace
Hrubý, Jan
We review some interesting aspects of the origin of the droplets by atomization or vapor-liquid nucleation, measurement of droplets by light scattering, and separation of droplets. Production of small droplets around 10 microns requires high pressure spraying or two-phase nozzles with help of high pressure gas. Smallest droplets – from 1 nm – can be formed by vapor-liquid nucleation processes. Application of the constant angle Mie scattering method enabled measurement of fast growing droplets in the range of 300 nm to 2000 nm. Examples of separation of droplets using inertial effects are given.
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Kavitační bublina v blízkosti pevné stěny
Müller, M. ; Zima, Patrik
The article presents the results of the calculation of the cavitation bubble collapse near a solid boundary. The solution is obtained using the FLUENT CFD software. The VOF (Volume Of Fluid) model is applied to study the behavior of the interphase between the liquid and the bubble content. The calculations were performed for three different distances of the bubble from the solid wall. The evolution of the bubble radius is obtained from the phase interface contours. The bubble jet velocity and its thickness are determined for all bubble positions.
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Experimentální výzkum kavitační bubliny ve vodě
Müller, M. ; Zima, Patrik
The article presents the results of experimental investigation of laser-induced cavitation bubble in water. The cavitation bubble is generated using the Q-switched Nd-YAG laser and recorded by a multi-exposure method, which allows to record the bubble at different phases into single frame.
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Zpracování informací získaných z termochromních kapalných krystalů
Tesař, Václav ; Randa, Zdeněk
Thermochromic liquid crystals respond to local changes of temperature by varying the colour of reflected light. Their use in experiments with anisothermal fluid flows seems to be simple - just taking pictures of the colours on the walls exposed to the fluid flow. However, practical extraction of quantitative informationfrom the pictures is not straightforward and brings a number of pitfalls. Unfortunately, these details are generally not found in available literature since most authors mention these practical procedure aspects very briefly, if at all. The present paper concentrates on these practical steps following them on a practicalexample of an investigation of an impinging jet, presenting the experience acquired in such investigations.
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Frekvenční charakteristika generátoru anulárního syntetizovaného proudu s velkým vnitřním průměrem
Krejčí, A. Petr ; Trávníček, Zdeněk ; Tesař, Václav ; Kordík, Jozef ; Pavelka, Miroslav
An annular synthetic jet actuator of large inner/outer diameter ratio of the nozzle has been developed, and four variants were designed, manufactured, and tested. The resonance frequency was estimated theoretically, based on the mechanical energy balance, and then measured by the pneumometric method. The resultant value was found to be 40 Hz. The nozzle geometry effect on the resonance frequency and on the velocity was quantified; both effects were concluded to be surprisingly small, less than 5%.
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Numerická simulace Kármánovy vírové řady za izotermických i neizotermických podmínek
Šponiar, D. ; Trávníček, Zdeněk ; Vogel, J.
This report deals with numerical simulation of the wake airflow behind a circular cylinder using FLUENT solver. The flow is assumed to be two–dimensional, laminar, and incompressible. The Reynolds number ranges Re = 30:-170. The isothermal numerical simulation agree very well with experimental data except the situation near the critical stage (between the steady and vortex shedding regimes); the maximum deviations of simulation and experiments are within 1.2%. The results obtained under the non-isothermal conditions are quite good – except the simulation near the critical stage, where the problems are similar as in the isothermal case.
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