Modeling Low-Energy Mixers for Chemical Dispersion in Water Treatment

Abstract

A study has been conducted to evaluate the use of computational fluid dynamics (CFD) for analyzing the mixing effectiveness of low-energy mixers in water and wastewater treatment processes. In this study, CFD was used to predict experimental downstream mean tracer concentration and segregation intensity in different closed conduit reactor geometries. Mixing configurations include a plane shear layer, plane jet in a square conduit, a round jet in a circular conduit, and a hydraulic jet in a 1- and 6-in. diameter pipe. Tracer transport was approximated as a single fluid with the standard k-∊, Chen-Kim k-∊, RNG k-∊ turbulence models and as a multifluid with the standard k-∊ turbulence model. The results showed that the multifluid model better predicted the mean concentration than the single-fluid model. Multifluid model r² values were significantly higher than the single-fluid model r² values. The multifluid model also predicted the downstream segregation intensity values for the plane jet and round jet configurations. In addition, the multifluid model was able to predict the degradation in mixing performance moving from the 1- to 6-in. diameter hydraulic jet mixers operating under constant-jet momentum ratio. No significant improvement was found in the single-fluid model predictions by changing the turbulence model. Overall, the results show that CFD has the potential to enhance engineering experience by permitting the evaluation of different low energy-mixer alternatives.