Vendredi 24 mars 2017 : Thèse de Lixia YANG
La thèse se déroulera le vendredi 24 mars 2017 à 10h : INSA de Toulouse, 135 Avenue de Rangueil, 31400 Toulouse (Amphithéâtre Riquet)
Intitulé de la Thèse :
"Local investigations of gas-liquid mass transfer around Taylor bubbles flowing
in straight and meandering millimetric channels using a colorimetric method"
M. Philipp RUDOLF VON ROHR, ETH Zürich (Rapporteur)
Mme Katharina ZAHRINGE, University of Magdeburg (Rapporteure)
M. Yves GONTHIER, Université de Savoie (Examinateur)
M. Jean-Marc COMMENGE, Université de Lorraine (Examinateur)
M. Gilles HEBRARD, INSA de Toulouse / LISBP (Directeur de thèse)
M. Christophe GOURDON, INP de Toulouse / LGC (Directeur de thèse)
M. Nicolas DIETRICH, INSA de Toulouse / LISBP (Co-encadrant)
Mme Karine LOUBIERE, CNRS / LGC (Co-encadrante)
Compact Heat-EXchanger reactors (HEX) are an important part of process intensification technology. However, most of the existed research dealing with such type of equipment is focused on the application of one-phase reactive flows. For gas-liquid reactions (e.g. hydrogenations, photooxygenations, fluorinations), few investigations have been carried out, whereas such multiphase systems still raise many fundamental questions, in particular with respect to the understanding of the coupling between transport phenomena and reaction kinetics.
With regard to this context, this thesis aims at locally studying gas-liquid mass transfer around Taylor bubbles flowing in straight and meandering millimetric channels ; this is a preliminary step essential before implementing two-phase reactive systems. For that, the socalled colorimetric method was implemented. Based on the use of an oxygen sensitive dye, this innovative method enabled the equivalent dissolved oxygen concentration field around bubbles to be visualized without any laser excitation or inserting a physical sensor, and then is convenient and user friendly. Firstly, it was necessary to investigate the occurrence of a possible enhancement of the gasliquid mass transfer by the chemical reaction involved. For that, as data on the associated kinetic are seldom in the literature, the reaction characteristic time was firstly estimated by carrying out experiments in a microchannel equipped with a micromixer.
The diffusion coefficients of dihydroresorufin and O2 were then determined by implementing two original optical methods in a specific co-flow microchannel device, coupled with theoretical modelling. The knowledge of these parameters enabled to calculate the Hatta number and the enhancement factor, and then to give complementary information about the reliability of the colorimetric technique to characterize the gas-liquid mass transfer in milli/micro systems. Secondly, a special focus was made on the study of the gas-liquid mass transfer occurring in Taylor flows right after the bubble formation stage in a flow-focusing microreactor. The results highlighted that the contribution of the bubble formation stage to the overall gas-liquid mass transfer stage was very important.