The flow structure of the dispersed gas phase within an aerated stirred tank reactor of pilot scale (600L) has been investigated by means of a new ultrasound reflection technique. A compact implementation of the new measuring technique is described in this article. It allows the investigation the flow structure of the dispersed gas phase in real multiphase flows within arbitrary large reaction vessels. Measurements have successfuly been performed even in complex biotechnological and chemical production systems. The measuring device exploits the Doppler-shift of ultrasound pulses upon reflections at the surfaces of moving bubbles. Only a single measuring probe needs to be introduced into the dispersion. Bubble velocity distributions can be obtained within a few minutes, even during production processes in highly viscous media. The device is simple to use, since it is fully automized by means of integrated microprocessors.On a CtudiC la structure de I'Ccoulement de la phase gazeuse disperste dans un rCacteur agitC aCrC ?i I'Cchelle pilote (600 L) au moyen d'une nouvelle technique de rkflexion B ultrasons. On dCcrit dans cet article la faqon dont a miniaturisi la technique de mesure. Cette technique permet l'btude de la structure de I'Ccoulement de la phase dans des Ccoulements multiphasiques reels ?i I'intCrieur de grands rkacteurs. On a m&me rCussi ?i effectuer des mesures dans des rkacteurs biochimiques et chimiques complexes. Le systbme de mesure exploite le dCcalage par effet Doppler de la frCquence de pulses ultrasonores causC par la rhflexion des ondes sur la surface de bulles en mouvement. II n'est nkcessaire d'introduire qu'une seule sonde de mesure dans la dispersion. Les distributions de vitesse des bulles peuvent &tre obtenues en quelques minutes, mCme durant les procCdCs de production dans des milieux trks visqueux. Le systbme est facile ?i utiliser du fait qu'il est complbtement automatis6 au moyen de microprocesseurs intCgrCs.
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