title: Experimental testing and modeling analysis of solute mixing at water distribution pipe junctions.
abstract: Flow dynamics at a pipe junction controls particle trajectories, solute mixing and concentrations in downstream pipes. The effect can lead to different outcomes of water quality modeling and, hence, drinking water management in a distribution network. Here we have investigated solute mixing behavior in pipe junctions of five hydraulic types, for which flow distribution factors and analytical equations for network modeling are proposed. First, based on experiments, the degree of mixing at a cross is found to be a function of flow momentum ratio that defines a junction flow distribution pattern and the degree of departure from complete mixing. Corresponding analytical solutions are also validated using computational-fluid-dynamics (CFD) simulations. Second, the analytical mixing model is further extended to double-Tee junctions. Correspondingly the flow distribution factor is modified to account for hydraulic departure from a cross configuration. For a double-Tee(A) junction, CFD simulations show that the solute mixing depends on flow momentum ratio and connection pipe length, whereas the mixing at double-Tee(B) is well represented by two independent single-Tee junctions with a potential water stagnation zone in between. Notably, double-Tee junctions differ significantly from a cross in solute mixing and transport. However, it is noted that these pipe connections are widely, but incorrectly, simplified as cross junctions of assumed complete solute mixing in network skeletonization and water quality modeling. For the studied pipe junction types, analytical solutions are proposed to characterize the incomplete mixing and hence may allow better water quality simulation in a distribution network.
authors.affiliation: Department of Civil Engineering, Zhejiang University, Hangzhou 310058, China; Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, MO 63130, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Shao
authors.affiliation: U.S. EPA, Office of Research and Development, National Risk Management Research Laboratory, Cincinnati, OH 45268, USA. Electronic address: yang.jeff@epa.gov.
authors.forename: Y
authors.initials: Y
authors.lastname: Jeffrey Yang
authors.affiliation: Department of Civil Engineering, Zhejiang University, Hangzhou 310058, China.
authors.forename: Lijie
authors.initials: L
authors.lastname: Jiang
authors.affiliation: Department of Civil Engineering, Zhejiang University, Hangzhou 310058, China.
authors.forename: Tingchao
authors.initials: T
authors.lastname: Yu
authors.affiliation: Department of Civil Engineering, Zhejiang University, Hangzhou 310058, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Shen
mesh_terms: D012498:Sanitary Engineering; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D014881:Water Supply / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical
keywords: Cross junctions; Double-Tee junctions; Drinking water distribution; Solute mixing; Water quality modeling