Empirical Reynolds number model for drag coefficient determination of ballasted flocs

Abstract

Transition of hybrid natured ballasted flocs in fluid medium (reflected by Reynolds number: Re) is highly important characteristic influencing performance of ballasted flocculation. Previous studies exhibited Re dependent on velocity of falling particles, which is a complex phenomenon to observe directly. The purpose of this study was to develop an empirical Re model independent of the velocity of settling flocs. An image analysis method was adopted for real time observations of the distinct settling phenomenon of ballasted flocs. The regression analysis was then applied to establish an empirical Re model independent of settling velocity of ballasted flocs. The proposed Re model was statistically evaluated and found effective with 85 % agreement to experimental Re observations. The developed Re model was extended for drag coefficient (Cd) determination of ballasted flocs and was capable of precisely predicting Cd (76 % agreement) in comparison with the recently developed empirical Cd - Re models (developed for studying irregularly shaped particles). Therefore, the developed model can be successfully adopted to determine the Re and can be extended to precise determination of Cd. This can lead to effective designing of ballasted flocculation treatment facility.