Assessment of the minimal distance for placing household connections downstream of water distribution cross junctions

Abstract

Abstract This study investigates the solute (chlorine residual) mixing phenomena downstream of a cross junction, considering its critical role in household connections. Experiments were conducted under turbulent flow conditions in a cross junction with two inlets at 90°, varying flow and chlorine concentration ratios at the inlets, i.e., simulating conditions commonly found in real water distribution systems. Results show that outlet chlorine concentrations primarily depend on the flow ratio at the inlets as well as on the inlet chlorine concentrations. Three-dimensional simulations were conducted to predict chlorine concentrations downstream of the cross junction. To evaluate the degree of downstream mixing, the percent coefficient of variation of tracer concentration (%CV) as a function of the axial position at different chlorine and flow ratios was computed from simulations. It was found that the flow ratio strongly affects it at downstream distances less than 50 pipe diameters, whereas the inlet chlorine concentration ratio has a weak effect. A novel correlation was derived as a function of flow ratio to ascertain the minimal distance for achieving the intended mixing level of %CV = 5 downstream of cross junctions. This correlation holds potential as a criterion for household connection location within water distribution networks for high-quality water delivery.