This study is aimed at elucidating the mechanism by which rising air bubbles induce shear stress on hollow fibre membrane surfaces. Shear stress on hollow fibre membrane surfaces (laterally-set and vertically-set) caused by aeration was measured directly using a two-direction load sensor. In the laterally-set hollow fibre module, time-averaged upward-direction shear stress on the membrane surface was compared to theoretical shear stress values considering the effect of water flow on membrane surface. Measured time-average shear stress values were almost 200 times larger than theoretical values implying strong interactions between bubbles and solid surface. In the vertically-set membrane module, velocity measurement of bubble flow using laser Doppler velocimeter revealed that drag force working on membrane surface was closely related to upward-direction water velocity. Also fluctuation of drag force and shear force on membrane surface was found to be related to velocity fluctuation (turbulence).
Effect of bubble flow velocity on drag-force and shear stress working on submerged hollow fibre membrane
H. Nagaoka, M. Kurosaka, N. Shibata, M. Kobayashi; Effect of bubble flow velocity on drag-force and shear stress working on submerged hollow fibre membrane. Water Sci Technol 1 November 2006; 54 (10): 185–192. doi: https://doi.org/10.2166/wst.2006.818
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