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Mise au point d’une nouvelle méthode optique pour la mesure de concentration locales en phase liquide : application au mélange dans une cuve agitée

Abstract : aLitterature review showed the conventional concentration probes are now limited both in size and frequency cutoff. Fluorescence spectroscopy seemed promising. Theoretical basis and applications study explain how it can provide spectral, spatial and temporal resolution indispensable to improve local concentration measurements. Difficulties when studying the elements of the experimental setup are described with their complete adjustments. Characteristic electrical and mechanical noises and corresponding remedies, when existing, are give. The absorption-emission stochastic process involved by the fluorescence of the tracer appears to depend on a Poisson statistic : direct proportionality no more exists between local concentration and measured signal. But relationships between their statistical properties have been established, with the corresponding signal processing only able to eliminate the superimposed random noise pollution. The mixing of two feed streams in a standard continuous stirred tank, one with the fluorescent tracer, the other without, results in a turbulent fluctuating concentration field, used to validate the sensor. Theoretical predictions for the signal processing appear to be relevant. Effects of position, stirring speed, mean residence time and viscosity were studied on local intensity of segregation, spectral density functions, power dissipation spectra and autocorrelations. Minimum values for stirring speed or mean residence time seem to exist, above which fluctuations are no more detectable. Dimensionless reduced spectra take a unique shape, as predicted by the turbulence theory. Viscosity, while increasing segregation, seems no to influence spectra because the Schmidt number was probably not modified. Perpectives of improvement are suggested
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Submitted on : Thursday, March 29, 2018 - 1:33:47 PM
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Pascal Vacus. Mise au point d’une nouvelle méthode optique pour la mesure de concentration locales en phase liquide : application au mélange dans une cuve agitée. Autre. Institut National Polytechnique de Lorraine, 1991. Français. ⟨NNT : 1991INPL080N⟩. ⟨tel-01752182⟩



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