Local gas hydrodynamics in an external-loop airlift reactor: newtonian andnon-newtonian fluids

Measurements of local gas phase characteristics are obtained in an external -loop airlift reactor filled with newtonian or viscous non-newtonian liquid s. A double-optical fiber probe technique is used. It allows the determinat ion of the axial and radial profiles of gas hold-up, bubbling frequency, bu bble size and velocity. In the case of air-water system, the results show a strong effect of radial liquid velocity variation on the gas flow characte ristics at the bottom of the riser. In the case of highly viscous non-newto nian solution, the gas flow is strongly affected by the gas distribution ju st above the gas sparger. This study also points out the bubble coalescence and the break-up phenomena in different liquids and levels in the reactor. Furthermore, the local measurements of bubble size and velocity allows to gain more detailed information on the dynamics of the bubble-flow and shows a tendency of large bubbles to circulate in the column center.