The role of cross-sectional geometry on oxygen transfer in high-head conduits

Oxygen is used in biological activities and chemical reactions occurring in water. As a result of these reactions and activities, the dissolved oxygen concentration in the water decreases. The dissolved oxygen concentration value required for the continuity of life of living things is 5 mg/L. The fact that the oxygen value is below this level poses a danger to the continuation of life. In order for the decreased oxygen level to reach the optimum value, the oxygen taken from the air must be added to the water. This process, called aeration, is carried out using hydraulic structures. For aeration to be done quickly and efficiently, air bubbles must enter the water quickly. The presence of air bubbles in excess will increase the surface area required for transfer and will ensure rapid oxygen recovery. Aeration with hydraulic structures is economically more advantageous because less energy is used and oxygen transfer efficiency is higher than conventional aeration methods. In recent studies, two-phase flow systems have been obtained with the air taken from the atmosphere in different ways into high pressure pipes. It has been determined as a result of the studies that the small air bubbles taken into the pipe increase the surface area required for oxygen transfer and perform the air transfer quickly. Based on these studies, oxygen transfer efficiencies were investigated by taking into account different cross-section shapes, different pipe narrowings, different lengths, different valve types and different flow rates of high-pressure capped conduits, which can be shown as an alternative to existing aeration systems in the aeration process in water engineering. From the results obtained, it was seen that the cross-sectional shape had a significant effect on the oxygen transfer efficiency in high pressure capped conduits. As a result of the experiments, it was observed that the oxygen transfer efficiency increased with the increase of the gate opening ratio and the highest oxygen transfer was achieved in the 60x100 rectangular cross-section conduits.