Flow induced by a single rising bubble between parallel walls

Abstract

This study aims to investigate the characteristics of the flow field caused by a single rising bubble between parallel walls (i e the virtual geometry in flat-sheet membrane bioreactor) Particle Image Velocimetry (PIV) and multi-time interval velocity calculation method were conducted to measure the flow field caused by a 3 ml bubble To simulate the rheological behavior of sludge a transparent rheological fluid carboxymethyl cellulose (CMC) was prepared in various level (0% - 0 15%) for PIV measurement The time-series analysis result showed that the velocity increased exponentially followed by achieving bubble buoyancy velocity with high reproducibility among 30 times repeated tests for each case when the rising bubble closing to the measuring point from bottom However the following flow field varied a lot after bubble passing through the point among three tested CMC solutions Briefly maximum rising velocity could be 1 4 – 2 0 times higher than bubble buoyancy velocity both in long side and short side of rectangular tank and wake developed with high turbulence in clean water while the velocity dropped down quickly with less turbulence in 0 15% CMC solution Considering the shear stress near the wall the maximum shear stress was found about 1 4 Pa for 0 15% CMC 0 8 Pa for 0 05% CMC and only 0 6 Pa for clean water according to Sisko model for non-Newtonian fluid even though both velocity and corresponded shear rate were higher in clean water rather than in high viscosity CMC solution

Date of Award	2020
Original language	English
Supervisor	Shih-Chun Hsiao (Supervisor)