DeMoyer Connie D, Schierholz Erica L, Gulliver John S, Wilhelms Steven C
St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, Mississippi River at 3rd Avenue, SE, Minneapolis 55414, USA.
Water Res. 2003 Apr;37(8):1890-904. doi: 10.1016/S0043-1354(02)00566-3.
The primary location of oxygen transfer in a diffused aeration system is examined by separately determining the surface air-water and bubble-water mass transfer coefficients. The mass transfer model developed to determine the mass transfer coefficients advances the McWhirter and Hutter (A.I.Ch.E. J. 35(9) (1989) 1527) model by tracking oxygen and nitrogen transfer into and out of the bubbles as they rise to the water surface. The resulting vertical profiles of the liquid-phase equilibrium concentration inside the bubble and the gas-phase oxygen composition give insight into how the bubble-water concentration gradient changes over depth. The surface mass transfer coefficient, k(Ls)a(s), is 59-85% of the bubble mass transfer coefficient, k(L)a(b), and the driving concentration difference is smaller for surface transfer. Surface transfer and bubble transfer both contribute significantly to oxygen transfer; however, bubble transfer is the primary mode of oxygen transfer for this system at the air flow rates used. Further experiments demonstrate that most of the surface transfer occurs above the bubble plume.
通过分别测定气-水界面和气-泡界面的传质系数，研究了曝气系统中氧气传递的主要位置。为确定传质系数而建立的传质模型改进了McWhirter和Hutter（《美国化学工程师学会杂志》35(9) (1989) 1527）的模型，该模型通过跟踪气泡上升至水面过程中氧气和氮气进出气泡的情况来进行研究。由此得出的气泡内液相平衡浓度和气相氧气组成的垂直分布，有助于深入了解气泡-水浓度梯度随深度的变化情况。气-水界面传质系数k(Ls)a(s)为气泡传质系数k(L)a(b)的59-85%，且气-水界面传质的驱动浓度差较小。气-水界面传质和气泡传质对氧气传递均有显著贡献；然而，在所使用的空气流量下，气泡传质是该系统氧气传递的主要方式。进一步的实验表明，大部分气-水界面传质发生在气泡羽流上方。
