The effect of liquid viscosity on hydrodynamics and bubble behaviour of an external-loop airlift reactor within air-water system were studied by an electrical conductivity probe. Carboxyl methyl cellulose (CMC) was used to change liquid viscosity (1.00-51.25 cP). Gas holdup increased with superficial gas velocity increasing, as well as bubble Sauter diameter and bubble rise velocity. With liquid viscosity increasing, average gas holdup increased first then decreased, while bubble Sauter diameter was opposite, with critical viscosity l ≈ 3.7 cP. The cross-sectional average bubble Sauter diameter increased obviously after l > 3.7 cP, and its size distribution was wider within the higher viscosity. Bubble rise velocity increased significantly and nearly unchanged after l > 10.3 cP. Gas holdup first increased then remained unchanged with the axial height increasing. The radial profile of local gas holdup presented a central peak distribution, and the value at inlet was smaller than that at the higher position. Average gas holdup was correlated greatly with superficial gas velocity and liquid viscosity.
-Hydrodynamics of an AirLift Reactor (ALR) with tap water and non-Newtonian fluid was studied experimentally and by numerical simulations. The Population Balance Model (PBM) with multiple breakup and coalescence mechanisms was used to describe bubble size characteristics in the ALR. The interphase forces for closing the two-fluid model were formulated by considering the effect of Bubble Size Distribution (BSD). The BSD in the ALR obtained from the coupled Computational Fluid Dynamics (CFD)-PBM model was validated against results from digital imaging measurements. The simulated velocity fields of both the gas and liquid phases were compared to measured fields obtained with Particle Image Velocimetry (PIV). The simulated results show different velocity field profile features at the top of the ALR between tap water and nonNewtonian fluid, which are in agreement with experiments. In addition, good agreement between simulations and experiments was obtained in terms of overall gas holdup and bubble Sauter mean diameter.
NOMENCLATURE SymbolsVolume fraction of gas/liquid phase, 1 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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