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Characterization of fluctuating discharge
Chumak, Oleksiy ; Hrabovský, Milan
A digital camera coupled with computer has a great potential in an analysis of discharges structures. This work analyzes an approach to visualization of dynamic radiant object. Mapping of brightness uncertainty values is used to show regions of different fluctuation intensity of radiation. The entropy as described by information theory was used as a relevant parameter for an uncertainty value. By a mathematical procedure a relative parameter based on the entropy was evaluated. As result an effects of optics sensitivity or of imperfections of experimental set-up were significantly suppressed.
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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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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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