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Phase Coupling Between Core and Boundary Regions of a Thermal Plasma Jet
Hlína, Jan ; Šonský, Jiří
Time series of plasma jet radiation distributions in planes perpendicular to the jet axis were analyzed by the fast Fourier transform (FFT). Complex output yielded by FFT was used to study amplitudes and phase angles belonging to various frequencies occurring in the frequency spectra. The distributions of amplitudes and phase angles have shown the existence of characteristic core and boundary regions for various types of oscillations. Phase angle relations give evidence of coupling between the core and boundary of the jet at some frequencies.
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Dependence of Thermal Plasma Flow Velocity on Arc Current Determined by Correlation Analysis of Optical Records
Gruber, Jan ; Šonský, Jiří ; Hlína, Jan
Optical radiation of thermal plasma jet was recorded in two parallel cross-sections perpendicular to the jet axis and separated by 3.5 mm. Sufficient sampling rate was a prerequisite to obtain detectable shift between the time-series recorded in closer and farther cross-sections. We have determined time lags between the recorded signals both in the core and boundary regions by correlation analysis and subsequently determined associated velocities of plasma flow. Arc current was gradually increased in respective measurements, gas flow was fixed. Determined flow velocities are in the range 140 m/s - 280 m/s in the jet core and 110 m/s – 220 m/s in the boundary region. This is in agreement with the results obtained for similar plasma torches by other methods in the past. Velocity increases with arc current almost linearly and this dependence and velocity profile in the plasma jet cross-section are presented in this paper.
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Multilevel IGBT pulse-controlled rectifier
Bejvl, Martin ; Šimek, Petr ; Škramlík, Jiří ; Valouch, Viktor
A low voltage PWM rectifier 5 kVA based on IGBT multilevel converter has been developed. It is characterized by a low THD value of the grid current and can change the power factor. The modular arrangement of a grid filter makes it possible to test either L or LCL type of grid filters of different parameters. The PWM rectifier is equipped with the vector control of the grid current and superimposed feedback loop of dc voltage.
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High Power PWM rectifiers
Valouch, Viktor ; Šimek, Petr ; Škramlík, Jiří
High power, high voltage PWM rectifiers with low swirching frequency are analyzed in terms of attainable powers exchangedwith the grid and of their current frequency spectra. Four-level PWM rectifiers with rated powers S = 2, 4, 8 MVA and the switching frequency 800 Hz per one switching element are considered, thus the controlller sampling frequency 1600 Hz is used. Selected results of simulation as wellas experimental tests are presented.
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Studie integrálního uspořádání magnetohydrodynamického čerpadla pro transport roztavených kovů či solí
Kotlan, V. ; Doležel, Ivo ; Ulrych, B.
The paper deals with one of the fundamental possibilities of improving magnetohydrodynamic (MHD) pumps based on the integration of effects of elementary MHD minipumps distributed along the pipe through which they transport the considered liquid. The crucial point of the work consists in computer modeling of this integral arrangement (system of minipumps) and presentation of the results that demonstrate their advantages–reduction of electric currents flowing through the minipumps and consequent reduction of the total ohmic losses in the system.
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Studie vhodného uspořádání magnetických obvodů pro realizaci magnetokalorického efektu
Doležel, Ivo ; Ota, J. ; Ulrych, B.
The paper is stimulated by one of very prospective physical do-mains – magnetic cooling based on the magnetocaloric effect. Successful realization of this effect requires a magnetic circuit with permanent magnets producing very strong and uniform magnetic field and the paper deals with arrangements of such circuits. Its crucial point consists in the presentation and consequent discussion of the results that allow estimating the suitability of the considered magnetic circuits.
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Statické charakteristiky konstrukčních částí řiditelného termoelastického aktuátoru
Doležel, Ivo ; Kotlan, V. ; Ulrych, B.
The paper deals with one of the basic conditions of practical employment of finely controllable thermoelastic actuators – problems of the static characteristics of its individual structural parts. It contains the formulation of the principle of such thermoelastic actuators, description of its components (a dilatation element heated by induction, auxiliary electromagnetic actuators, and self-locking friction clutches) and their mathematical models. Briefly discussed are also their corresponding computer models making use of the finite element method. The crucial point of the work consists in the presentation of the results – static characteristics of the considered structural parts of the controlled thermoelastic actuators.
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