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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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Vliv nestabilit na určení střední teploty ve volném proudu termického plazmatu
Hlína, Jan ; Šonský, Jiří ; Šlechta, Jiří
We have used results acquired by a multi-directional optical system for temperature measurements with a high temporal resolution to compare mean temperatures in the jet obtained by averaging the instantaneous temperature fields with the temperature values acquired in the usual way from averaged radiation intensities. The comparison shows differences in results yielded by both methods which are caused by the nonlinear dependence of radiation intensity on temperature.
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3D diagnostika koherentních struktur ve volném proudu plazmatu
Hlína, Jan ; Sekerešová, Zuzana ; Šonský, Jiří
Optical radiation of a thermal plasma jet was recorded by a fast - shutter CCD camera through an optical system providing two perpendicular and simultaneous views of the jet. The measuring system yielded series of plasma jet images containing 8 pictures with exposure times 400 ns and intervals 7 us. The evaluation of the records was based on reconstructing the distribution of plasma optical radiation in planes perpendicular to the plasma jet axis by the inverse Radon transform. A repetitive application of this transform along the axis of the jet yielded the complete 3D distribution of the optical emission in the plasma jet. The differences between the resulting 3D matrices representing the optical intensities derived from adjacent pictures in the recorded series was used for the identification of coherent structures as regions characterized by the temporal increase or decrease of the optical emission.
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Studium expandujícího proudu termického plazmatu s využitím molekulových spekter
Mašláni, Alan ; Sember, Viktor
Thermal plasmas generated by plasma torches are well-known for their high temperatures and high enthalpies. Therefore optical emission spectroscopy is appropriate diagnostic method because of strong emission of radiation corresponding to the visible light. The decay of excited atoms, ions and molecules causes emission of the light at characteristic wavelengths. Except spectral lines of atoms and ions, also some molecular bands can be seen in the spectra of the plasma jet. Especially expanding thermal plasma jet operated under low pressure conditions offers possibility of observing molecular transitions. Pressure lower than atmospheric may cause the presence of supersonic flow and departures from thermodynamic equilibrium. Spectra of OH radical have been investigated using computer code LIFBASE, which contains a lot of data regarding spectra of diatomic molecules. Radial profiles of rotational and vibrational temperatures have been found in several regions of the jet.
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