Prediction of chlorine concentration of flows exiting pipe in cross junctions: experimental and numerical study

Abstract

Abstract This paper aims to develop and validate an analytical equation to predict the concentration of residual chlorine exiting a typical pipe junction. In order to investigate the trend of the incoming flow rates before leaving the junction, experiments with inflow rates (North and West) ranging from 0.18 to 2.17 L/s, Reynolds numbers ranging from 14,324 to 110,780, and free chlorine concentrations ranging from 0.5 to 1.80 mg/L were performed. The results showed that flows tend to bifurcate rather than mix completely, and the bifurcation and mixing depend mainly on the relative flow rates entering the cross junction. Based on the experimental results, a dimensionless concentration (R) was estimated, allowing for predicting chlorine at the East outlet. Then, a solute mass balance was also performed within the cross junction to predict chlorine concentration at the South outlet. Finally, an adjustment of the R-value was performed by using 3D computational fluid dynamics (CFD), and the analytical equations were also validated with simulations. The standard k–ε turbulence model with enhanced wall treatment for modeling turbulence and near-wall effects, respectively, were used. More mixing models will improve water quality simulations to ensure proper control of chlorine and possible contaminants in water distribution systems.