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Vysokonapěťový pulzní zdroj a řídící jednotka
Gruber, Jan ; Janovec, Jiří ; Šonský, Jiří ; Němec, Tomáš
Zpráva obsahuje popis sestavy vysokonapěťového pulzního zdroje (PPSU) a řídící jednotky (SPCU), které jsou využívány v kombinaci s výbojovou komorou a párem elektrod k aerosolové syntéze nanomateriálů. Uvedena jsou schémata zapojení, seznam elektronických i mechanických součástek, jakožto i popis konektorů a zřetězeného propojení více soustav. Zpráva rovněž obsahuje informace o referenčních parametrech výbojů a popis komunikačního protokolu včetně nastavitelných proměnných.
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Plasma-discharge control in fluidics
Tesař, Václav ; Šonský, Jiří
A transducer controlling fluid flow by electric signals without the two-stage conversion involving moved or deformed components have been so far unrealisable. Authors solved the problem by means of “ionic wind” of non-temperature plasma discharge acting inside a fluidic diverter amplifier. Experiments demonstrated good performance at high frequenciesf > 100 Hz and small Reynolds numbers Re <1000.
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Analysis of thermal plasma radiation by Fourier transform, wavelet analysis and phase portraits
Gruber, Jan ; Šonský, Jiří ; Hlína, Jan
Combination of various methods for signal analysis, including Fourier transform, wavelet analysis and time-embeddings provide alternate views on thermal plasma dynamics. We have recorded and analyzed radiation of cutting plasma torch during the whole cathode life-cycle (from the new unworn cathode to the cathode failure). Changes in dynamics during cathode lifecycle lead to regular oscillations expressed in signal spectra, in sudden discontinuities caused by released molten particles detected by wavelet analysis and overall dynamics change expressed in reconstructed phase portraits by time-embeddings. We present all these various views on changing dynamics to illustrate complexity of this dynamics.
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Mechanism of Multiple Microbubble Conjunctions
Tesař, Václav ; Šonský, Jiří
In typical generation of microbubbles by blowing the gas through tiny holes in an aerator, the size of bubbles is much larger than hole exit diameter. Explanation for this discrepancy was found by analysing high-speed camera images of bubble generation. Primary microbubbles, of initial size corresponding to the aerator exits, tend to remain near the location of their formation at the aerator exit - and coalesce there with subsequently formed other primary microbubbles. Typically, this coalescence is repeated several times before the increased final size and position of the resultant larger bubble reaches the limit for separation and ascent.
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Near-exit coalescence – a so far unknown limit to microbubble smallness
Tesař, Václav ; Šonský, Jiří
Gas bubbles in a liquid are required in applications to be of the smallest possible bubble size. Authors studied microbubble formation using a high-speed camera and discovered that bubbles increase their volume near the aerator exits by mutual coalescence. This effect presents a limit to how small microbubbles can be produced. The discovered conjunction effects are very fast and this is probably the reason why they have so far escaped attention.
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Observation of HF Cathode and ARC Root Inside Cutting Plasma Torch
Šonský, Jiří ; Gruber, Jan
Electric arc and a cathode of a cutting plasma torch was observed through fused silica window in a specially modified nozzle. Sample rate of used high-speed camera was up to 120 kHz, sufficient for detecting high-frequency fluctuations in arc plasma intensity, produced mainly by current ripple. Fluctuations were examined up to 60 kHz by Fast Fourier Transformation (FFT). Increased cathode material loss at start-up and shut-down phase of the plasma torch was observed. At start up phase, large number of small particles are ejected from the cathode. After electric current shuts down, large droplets of molten material are usually detected.
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Influence of Cathode and Nozzle Wear on Distributions of Fluctuations in Cutting Arc
Gruber, Jan ; Šonský, Jiří ; Hlína, Jan
Electric arc produced by cutting plasma torch was observed by CCD camera. Fluctuations in arc plasma intensity were examined in several frequency intervals up to 50 kHz and distributions of their intensities were compared. Plasma torch was operated repeatedly in fixed-time cycles resulting in progressive wear of cathode and nozzle. Changes in distribution of overall arc intensity are rather small, showing compression and expansion zones. However, distributions of fluctuations intensities differ significantly during the nozzle lifecycle, exhibiting formation of double-layer structure and other noticeable changes. The fluctuation distributions are also influenced by frequency interval chosen for the analysis.
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METHODS OF IDENTIFICATION OF COUPLED VORTEX STRUCTURES IN MOTION
Něnička, Václav ; Tesař, Václav ; Šonský, Jiří
Flow visualisation was performed of sections perpendicular to the axis through a jet. It reveaedl surprising complexity in the mixing region (outside the jet core. The images were processed by correlation in sub-images showing vortical motions suggesting the twisting and braiding movements of hair when a plait hairdo is made. For evaluation authors found useful the theory that measures entanglement in fluids by the corresponding algebra of braiding movements.
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Volumetric Velocimetry and Accelerometry of Injected Particles in Thermal Plasma Jet
Šonský, Jiří
Measurements of the injected particles velocities and accelerations in the plasma jet are important for thermal plasma spraying technology improvement. Commonly used methods of optical diagnostic, such as particle image velocimetry (PIV) or particle tracking velocimetry and accelerometry (PTVA),are complicated due to strong optical self-emission of the plasma jet. We have developed 3-D variant of the PTVA, able to measure particle velocities and accelerations in hot core of the thermal plasma jet, as well as in surrouding areas, such as entrance of particle flow into the plasma jet.
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