Abstract
The flows in bubble columns and/or gas-lift reactors are driven by the buoyancy of the gas phase. The momentum transfer between the gas and liquid phases in the multiphase system has hierarchical structure from molecular scale to convection scale. In particular, the mass transfer between individual bubbles and the surrounding liquid is essential for a deep understanding of the buoyancy driven flows in a bubble column reactor. The target of the present paper is the local-scale structure of the liquid-phase motion surrounding a single bubble zigzag rising in a rest water column.
The liquid-phase velocities in the vicinity of the bubble were measured using an LDA; in addition the bubble motion of the center of gravity was simultaneously visualized using high-speed video cameras. The focal point of the LDA is automatically positioned on the orthogonal grid system via a three-axial precision stage. Employing a laser-beam passing sensor detecting the bubble to trigger the LDA measurement, the liquid-phase velocities at any period before or after passage of the bubble were measured and analyzed. The properties of the bubble were 2.78mm in equivalent diameter and 836 in the Reynolds number and oblate ellipsoidal. It rose zigzag with 8.7mm in amplitude, 62.5mm in wavelength, 165.7ms in period and 301.5mm/s in velocity.First three-dimensional velocity fields of the liquid phase around the bubble are obtained from the LDA results. Second the frequency of velocity components is analyzed, and characteristic frequencies are obtained. Finally a coupling mechanism of the liquid-phase and bubble motion is discussed
