The behaviour of three different liquid-gas slug flows (water, carboxymethyl cellulose and activated sludge) in a vertical tube was studied using a high speed camera (HSC). Experiments were performed using different flow rates and two tube diameters (6.3 and 9.9 mm). The observed difference in behaviour of the ascending gas slugs can be explained by the difference in viscosity of the fluids (Newtonian and non-Newtonian). Moreover, it was observed that the degree of coalescence of gas slugs is lower for non-Newtonian liquids and they behave like a succession of slugs without actually coalescing into a single larger gas slug. Finally, gas slug rising velocities were also extracted, but no subsequent difference in the rising velocities of the different fluids was found.
Keywords: coalescence, gas slug rising velocity, gas-liquid slug flow, side-stream membrane bioreactor, viscosity