Experimental evaluation of liquid circulation flow rate induced by an air-injection-type aerator

Abstract

Despite previous research efforts, there is a lack of experimental data on liquid circulation flow rates, particularly in real-scale facilities. The study aims to fill this gap by proposing a momentum transfer model using a gas–liquid separation flow to estimate inner flow in a real-scale air-injection-type aerator. The liquid circulation flow rate was evaluated using velocity measurements. The air supply pressure and dissolved oxygen (DO) were determined. Experiments were performed at depths of 0.90, 1.30, and 1.75 m. The effect of the inner diffuser was investigated at each depth. The inner diffuser reduced the circulation flow rate but increased the vertical upward flow velocity. For the deepest condition (1.75 m), the inner diffuser reduced the air supply pressure and increased the overall oxygen transfer coefficient. Momentum analysis indicated a suppression effect of the air velocity at the aerator exit owing to the inner diffuser. This indicated that an increase in the gas holdup owing to the deceleration of the air velocity at the aerator exit reduced the air supply pressure owing to the reduction in downstream pressure. This study provides valuable insights into aeration system optimization, considering factors such as energy efficiency and oxygen transfer effectiveness.