The application of eccentric rotating cylinder apparatus for the improved study of particle coagulation

Concentric rotating cylinder and turbulent mixing devices have been frequently used in studying mixing and particle coagulation. However, these apparatus develop simple laminar flow (concentric rotating cylinders) or do not have well-defined flow (turbulent mixing devices). In this work, the eccentric rotating cylinder apparatus was investigated to find applicability for the improved study of coagulation based on the modified analytical solution of Ballal and Rivlin. Various eccentricity ratios, rotation speeds and viscosities were simulated to obtain optimum operating conditions. Inertial forces working on the fluid increased as the eccentricity ratio and rotation speed increase. As inertial forces increase, the eddy developed in wide clearance was more skewed in the direction of rotation. Both root-mean-square velocity gradient and average principal strain-rate, were increased by increasing eccentricity ratio. avaerage principal strain-rate were linearly increased as rotation speed increases, which suggested that average prinipal strain-rate can properly represent mixing intensity. Comparison of average principal strain-rate and RMS velocity gradient revealed that RMS velocity gradient overestimated mixing intensity and its error increased as eccentricity ratio increases. This study showed that the eccentric rotating cylinder apparatus has a non-uniform velocity distribution with well-defined fluid dynamics. Therefore, the eccentric rotating cylinder apparatus can be applicable as a model flocculator. However, in order to achieve reliable model predictability, the fluid Reynolds number must be below 200.