Dissolved oxygen transfer along falling water jets with developing surface disturbance

The dissolved oxygen (DO) concentration is an important index of water quality. It has a significant impact on the biodegradation process in water and the survival of aquatic organisms. Low DO concentrations often exist and may result in a deterioration in water quality and an increase in wastewater treatment expenses. An analysis of the oxygen transfer efficiency as correlated with the flow characteristics of a falling jet could help to solve these problems. Experiments related to oxygen transfer along a falling water jet were conducted, and the effects of the flowrate ($Q$), falling height ($H$) and initial DO concentration ($c_u$) were considered. The results demonstrated that a falling jet in air could be an effective way of improving the DO concentration. The results also indicated that the oxygen transfer efficiency is linearly dependent on $c_u$ and has a negative exponential relation with $H$. To deeply analyze the oxygen transfer process, the jet disturbance process was divided into 3 parts for the first time based on flow features: a smooth zone, turbulent zone and breakup zone. The results showed that the jet outlet velocity had a limited influence on the smooth zone height but assisted in jet breakup. Thereafter, a correlation modeling DO reaeration along the falling jet considering jet disturbance characteristics was obtained. This correlation was also applied to predict the aeration efficiency in experimental cases from the literature and showed good agreement with the reported results.