Lu Cheng, Cheng Wen, Zhou Shengnan, Wang Min, Liu Jikai, Wan Tian
Institute of Water Resources and Hydro-electric Engineering, Xi'an University of Technology, Xi'an 710048, China.
School of Architecture & Civil Engineering, Xi'an University of Science & Technology, Xi'an 710054, China.
ACS Omega. 2021 Jan 19;6(4):2790-2799. doi: 10.1021/acsomega.0c05126. eCollection 2021 Feb 2.
Microporous aeration has been widely used to restore eutrophic water bodies. The gas-liquid mass transfer in the aeration process has a significant influence on the improvement of water quality. Therefore, the influence mechanism of oxygen mass transfer is worth studying. However, the influence of bubble movement characteristics on oxygen mass transfer has not been systematically studied. Thus, the present study explored the influence mechanism of microporous apertures on oxygen mass transfer in terms of bubble motion characteristics by investigating the oxygen mass transfer process and the feature of bubble movement under different aeration microporous aperture sizes. The results showed that the mass transfer efficiency was reduced as the micropore aperture increased from 200 to 400 μm. and the reduction rate was 7.17% when the aperture increased from 200 to 300 μm, which was lower than that from 300 to 400 μm (19.17%). Furthermore, the micropore aperture showed a positive correlation with the time-averaged velocity field. With the increase in aperture, the bubble velocity gradient (from the center to both sides of the edge) increased from about 0.2 to 0.4 m/s, which increased the oxygen mass transfer effect. The increase of micropore aperture caused the increase of average Sauter bubble diameter and the decrease of specific surface area of bubbles. In addition, the negative effects of the reduction of specific surface area and the shortening of bubble residence time on oxygen mass transfer efficiency were greater than the positive effects of the increase of turbulent kinetic energy. When the aperture changes from 300 to 400 μm, the shortening of bubble residence time should have played a major role. This study provides some theoretical parameters for investigating the mechanism of oxygen mass transfer in microporous aeration.
微孔曝气已被广泛用于修复富营养化水体。曝气过程中的气液传质对水质改善有显著影响。因此，氧传质的影响机制值得研究。然而，气泡运动特性对氧传质的影响尚未得到系统研究。因此，本研究通过研究不同曝气微孔孔径尺寸下的氧传质过程和气泡运动特征，从气泡运动特性方面探讨了微孔孔径对氧传质的影响机制。结果表明，当微孔孔径从200μm增加到400μm时，传质效率降低。当孔径从200μm增加到300μm时，降低率为7.17%，低于从300μm增加到400μm时的降低率（19.17%）。此外，微孔孔径与时间平均速度场呈正相关。随着孔径的增加，气泡速度梯度（从中心到边缘两侧）从约0.2m/s增加到0.4m/s，这增加了氧传质效果。微孔孔径的增加导致平均索特气泡直径增大，气泡比表面积减小。此外，比表面积减小和气泡停留时间缩短对氧传质效率的负面影响大于湍动能增加的正面影响。当孔径从300μm变为400μm时，气泡停留时间的缩短应起了主要作用。本研究为研究微孔曝气中氧传质机理提供了一些理论参数。
