Oxygen Transfer in Bubbly Turbulent Shear Flow
Subhash Jain, Kyung Soo Jun
The equation for oxygen transfer in a bubbly air-water turbulent shear flow in a vertical pipe is derived. Dimensionless variables that characterize the transfer coefficient are identified. Laboratory experiments are conducted for a range of water-flow velocities and air-flow rates, with and without tangential swirl. The overall transfer coefficient (Kla) is estimated from the measured dissolved oxygen response curves. The transfer coefficient (kL) is computed using measured bubble-size distributions. For a given air-water discharge ratio (Gl), a higher flow velocity yields a larger kL due to higher turbulence and bubble-surface renewal. For a given flow velocity, as Gl increases so does Kla, primarily because the total air/water interfacial area increases. The rate of increase of Kla, however, diminishes for larger Gl, because kL decreases with Gl. In this case the decrease in kL results from a reduction in the turbulence intensity per unit volume of air. The transfer coefficient normalized by the mean flow velocity varies inversely with Gl and directly with the Reynolds number. The effect of the swirl on oxygen transfer is found to be insignificant.
Available upon request at the American Society of Civil Engineer