Non‐invasive mixing time estimation in unbaffled stirred tank: An ultrasonic approach

Estimation of mixing time is an essential aspect in characterization of stirred tanks. In this work, we report a novel, non‐invasive technique to estimate mixing time in an unbaffled stirred tank using a contact type ultrasonic sensor. Variation in speed of sound in stirred tank is measured by ultrasound and is used to determine the mixing time of solutions. A sensing time of 16.6 ms (~60 Hz) is achieved which leads to an estimation of the mixing process dynamics under forced vortex conditions. The method is validated against colorimetric technique using a dye. The technique is thereafter used to determine mixing time under different operating (impeller speed) and geometrical (impeller design, vessel diameter, and off‐bottom clearance) conditions. Though the results presented are specific to unbaffled stirred tank, the method reported is general and can be used in any kind of stirred tank.