Development Of Junction Mixing Model For Water Quality In Water Distribution System

Recent studies have shown that the assumption of complete mixing used by the traditional software EPANET differs greatly from the actual mixing at junctions,resulting in considerable errors.The paper integrates the experimental data from previous researches and the results of U junctions in this study,to develop a new software EPANET-ZJU that allows to consider the incomplete water quality mixing of junctions based on the EPANET source code.Due to the lack of experimental data of U junctions(one of the Double-T junctions),a visual study was carried out to verify that the mixing at U junctions is not complete intuitively.The study found that the connecting pipe increases the mixing time and space,and the longer the connecting pipe,the more complete the mixing.When L/D?10,mixing degree of the junction is complete.Further,mixing at U junctions with different pipe diameter ratios under different hydraulic conditions was studied experimentally.The results show that the Reynolds number ratios at inlets and outlets,dimensionless connecting length(L/D)and pipe diameters' ratio have influence on the mixing characteristics of U junctions.It found that the mixing degree of U junctions becomes better first and then worse with the increase of Reynolds number ratios ReW/S and ReE-/N.Comparing the U and the N junctions,it found that when L/D is small,the U junctions shows a better degree of mixing than that of N junctions.In contrast,when the L/D is large,the mixing degree of U junctions is close to that of N junctions.This paper summarizes the junction types for incomplete mixing,and proposes the program for determining the type of junctions based on the topology geometry and hydraulic state.A secondary development based on the EPANET source code was carried out,a software EPANET-ZJU was developed.The software takes into account the various types of junctions that may produce incomplete mixing in the water quality simulation,such as cross junctions,N junctions and U junctions.The factors influencing junction mixing,ratio of diameters and flow regime,were taken into consideration in the new version.Compared to the existing water quality simulation software,the new software improves the accuracy of the water quality simulation.Simultaneously,this paper introduces the pre-judgment mechanism of geometrical features of junctions with incomplete mixing,which greatly improves the efficiency of junction identification.Moreover,the flow distribution coefficient f1 is introduced in the calculation of the concentration in outlets,solving the problem that dimensionless concentration C*cannot accurately predict the water quality of the junctions with different pipe diameters.The software EPANET-ZJU was applied to two network cases.The results also indicate the necessity to consider the junction with incomplete mixing in simu.Improved software EPANET-ZJU will be used in the prediction of disinfectant residues,the optimization of water quality monitoring sensors,the determination of pollutant source,etc.