Study on visualization of water mixing flows in a digester equipped with a vertical impeller by using radiotracers

A mixer with a new concept design has been adapted into water treatment plants. It reportedly cuts down the energy consumption of the mixer by the new mixer, which moves vertically and creates internal flows toward its bottom. However, no experimental observations have been made on the internal flow caused by a vertical impeller. In this study, a radiotracer experiment, radioactive particle tracking (RPT) technique, and particle image velocimetry (PIV) were carried out to visualize the flow in the mixer, and compared to each other. The results show that the flow patterns from these techniques are very similar to each other, and the performance of the mixer was good enough to mix the inner materials. •Radioisotopes were used to visualize the flow in a mixer tank.•A radioactive particle tracking technique with a radioisotope generator was carried out for the first time in the world.•The effectiveness of the new mixer was confirmed.