Hydrodynamics of slug flow applied to cross-flow filtration in narrow tubes

This article focuses on the characterization of slug-flow hydrodynamics in two sizes of tubular membrane re diameters (6 and 15 mm) to quantify the ma in mechanical phenomena involved iii the limitation of particle fouling dur ing cross-flow filtration of suspensions. By using a conductance probe tech nique, the flow structure was accurately identified for two geometries, nod noticeable differences tt ere observed in terms of void fractions, velocit ies and lengths of Taylor bubbles, and liquid slugs. This characterization allowed some data to be theoretically estimated (wall shear stress, "fallin g" film velocity: film thickness) thanks to the application of a phenomenol ogical model initially developed for oil pipes. The results obtained in a 1 5-mm tube showed that the ultrafiltration flux improvement experimentally a chieved with bentonite and yeast suspensions, was partly due to the increas e in the wall shear stress, induced by continuous gas sparging inside the t ubular filtration module. Other hydrodynamic phenomena linked to the quasi- periodic succession of Taylor bubbles and liquid slugs were also involved i n the control of the particle entrainment: intermittency frequency reversal of the wall shear stress instantaneous pressure variations in the long bub ble wake with a higher level of turbulence, and an enhanced local mixing.