Sondes optiques : innovations sur un capteur classique

¹ Laboratoire des Ecoulements Géophysiques et Industriels, LEGI de Grenoble
² Groupe d'Instrumentation et de Contrôle Electronique des Procédés, GICEP, Grenoble
³ doctorant rattaché au LEGI et GICEP

Abstract

Optical probes are an essential component of the two-phase flow instrumentation, but their performances are still not well known, mainly due to a bad control of their sensitive tip, and to defects in signal processing. The DER-EDF, the LEGI and the GICEP have grouped together in order to improve the mastership of such probes. New sensitive tips geometries have allowed to simultaneously measure the gas phase characteristic function and its velocity with a single probe. A dedicated real time signal processing has been elaborated: its performances render it quite objective. The measuring ensemble has been checked in various air-water flows. The discrepancy with reference mesurements lies between 0 and -13% for the void fraction as well as for the velocity, provided that the gas fraction is higher than 5%. Beside, the real time processing has been extended to double-probes, but, in that case, a criteria remains which must be set by the user. Calibrations of bi-probes exhibit an error on velocity as high as 30%. Thus, the measuring ensemble for single probes appears to be more reliable and accurate than the classical double-probe technique: it offers an elegant solution for the characterisation of gas/liquid flows. Various extensions are discussed.