Investigations on the effect of liquid viscosity on the flow behaviour in bubble columns using wire mesh sensors

Bubble column reactors have been used in chemical, petrochemical, biochemical, and pharmaceutical industries for various processes, e.g. partial oxidation of ethylene to acetaldehyde, Fischer-Tropsch (FT) synthesis (Deckwer, 1992; Fan, 1989). Depending on operating and design parameters, bubble column reactor may exhibits different flow regimes e.g. homogeneous, heterogeneous and churn turbulent flow regime. These flow regimes have entirely different hydrodynamic characteristic which results in different mixing as well as heat and mass transfer.
Different maps have been proposed to differentiate flow regimes (Krishna and Sie, 1994; Shah et al., 1982; etc.) in bubble column. However, these maps are mainly limited to low viscosity systems (air-water) at ambient conditions. Previous works suggest that liquid phase viscosity has also a significant effect on the hydrodynamic characteristics. It stabilizes the bubbly flow and thereby results in a increasing bubble coalescence rate and decreasing breakup rate which may advance the flow regime transitions. Only few studies (Ruzicka et al. 2003; Thet et al. 2006, etc.) have been reported on the effect of liquid viscosity on the gas holdup in a bubble column. However, in all the previous works, smaller column diameter (< 140 mm) was considered. The effect of liquid viscosity on the flow regimes transition and hydrodynamic properties in large columns are yet to be investigated.
Therefore, the present work aims to study the effect of liquid viscosity (pure water vs. water+ glycerol mixtures with viscosity in the range of 1 ≤ µL ≤ 60 mPa•s on gas holdup and bubble size distribution at different superficial gas velocities (0.02 < UG < 0.32 m/s) for two different bubble column diameters (DC = 150 and 400 mm). Furthermore, the effects of liquid viscosity and column diameter on the regimes transition and on their dynamic behaviour in bubble columns will be studied.