Mixing at Cross Joints with Different Pipe Sizes in Water Distribution Systems

Accurate prediction of mixing at cross junctions is important in water quality models because most of the intersecting pipes use cross junctions in water distribution systems. To describe the characteristics of complex mixing phenomena, an empirical mixing model at the cross joints is proposed based on a large number of experimental data. The orthogonal experiments by numerical simulations show that the diameter ratio of inlets and the Reynolds number ratios of inlets and outlets have a dominant effect on the solute mixing at cross junctions. These dominant parameters are then chosen to investigate the cross-joint mixing in the experimental setup. The results indicated that the cross joint connected by pipes with a large size difference has a more complete mixing than the one with a small pipe size difference, if other conditions are kept the same. The mixing formulas for solute concentrations at outlets are fitted by an improved particle swarm optimization (PSO) algorithm based on the experimental data. The interpolation method is used to obtain the mixing information for other diameter ratios of the inlets. The established mixing model can be incorporated into standard EPANET to analyze the water quality in water distribution systems.