Modelling Sauter mean diameter of dispersed phase drops in mixer tank using an axial spiral series stirrer

Abstract The Sauter mean diameter ( d 32 ) is crucial for optimizing the design of the extraction columns and mixer settlers. This study proposes a new model for predicting d 32 for mixing tank with an axial spiral series stirrer which includes baffles. The experiments were done under batch operation conditions. Water and dispersed phase consisting of the extractant Mextral 5640 H and kerosene were combined. Experiments were carried out under different operating conditions, including impeller speed, dispersion time, and dispersed liquid volume fraction (holdup). The drops were photographed at impeller speeds of 300 and 400 rpm, with holdups of 0.1, 0.2, 0.44, and 0.54, and times of 90, 180, 270, and 360 s. After considering the parallax error in the measurement of the drop diameter, d 32 was determined as a function of the operating parameters and physical properties using an image analysis technique. In addition, a prediction model of d 32 was established with 13.17% error. According to the model, as the impeller speed increases or the dispersed phase holdup decreases, d 32 decreases; additionally, over time, d 32 decreases until it reaches a characteristic asymptotic value, reflecting the dynamic balance between droplet breakup and coalescence. The comparison of the model parameters showed that the dispersion time effect is more influential than the impeller speed and holdup in terms of the average droplet size.