Numerical simulation of chloramines formation in turbulent flow using a multi-fluid micromixing model

A study has been performed to investigate the use of Computational Fluid Dynamics (CFD) for the analysis of ammonia injection methods to produce chloramines in water containing residual free chlorine. In this study, the Reynolds-averaged Navier–Stokes Equation and turbulence model were combined with chloramines kinetic models to predict downstream spatial distribution of residual free chlorine. As part of this study, a CFD model with the RNG k–ɛk–ɛ turbulence model was combined with a multi-fluid microscale model (MFM) to investigate the impact of micromixing on the free chlorine residual. All model predictions were compared with experimental measurements of the free chlorine residual at different upstream and downstream locations from the ammonia injection point. Three types of ammonia diffusers were simulated and tested in the presented work. The results showed that the incorporation of the MFM approach can enhance the numerical prediction of the free chlorine spatial distribution. In addition, the modeling results confirmed the experimental observation that multi-nozzle diffusers displayed better mixing performance than the cone-shape diffuser with a single nozzle in a pilot-scale reactor.