Experimental Study Of Solute Mixing At Junctions Under Low Velocity In Water Distribution Systems

When there are contaminations in the water distribution systems, water resource managers and engineers must determine the distribution of contaminations and give a corresponding counter-measures. Studying solute mixing at junctions in water supply systems is an important approach to analyze the distribution of pollutants. Recent studies focused on the mixing behavior at fully developed turbulence flows (Re> 10000), however, the research results on mixing at lower Reynolds number (Re<10000) were insufficient. The flows in the network will become laminar and transitional when water consumption is small or the flows are in suburban and peripheral. Nowadays, researchers always neglect the regime(Re<10000) mentioned above,hence, the prediction of the contaminants at junctions is largely misestimated. To predict the diffusion of malevolent or chemical pollution in the water distribution systems precisely and build a high accuracy water quality model, the mixing behavior under Re<10000 should be lucubrated systematically.Firstly, in order to examine the mixing phenomenon at junctions in a visualized way, we used red dye and DV to get the mixing images. The visualized results indicate that when the Reynolds numbers at the inlets and outlets are equal and Re< 10000, the Reynolds number affect the mixing degree obviously.Secondly, when Re<10000, experiments associated with different Reynolds number and various Reynolds number ratios at the outlets (ReN/ReE) were carried out, respectively. Results showed that the Reynolds number and Reynolds number ratios at the outlets (ReN/ReE) served an important role in the mixing. We also did the same experiment at DN16/DN25/DN32/DN50 cross junction to study the effect of pipe diameter size and we found that when the average Reynolds Numbers less than 3000, the bigger pipe diameter is, the better mixing degree will occur. The pipe diameter has almost no effect on the mixing when Re>3000.Thirdly,we examined the mixing phenomenon at the double-Tee joints considering Reynolds number?Reynolds number ratios at the outlets (ReN/ReE) and the dimensionless connecting pipe length ( L/D) . The results indicate that the Reynolds number and Reynolds number ratios at the outlets (ReN/ReE) do have an impact on mixing degree, but is not obvious. The mixing at the double-Tee joints in large L/D is obvious better than that in the small L/D.Finally, we introduced numerical simulation as a tool to examine the mixing phenomenon at the cross junction(DN25)with different Reynolds Numbers. According to the data of the numerical simulation result, we can conclude that the solute mixing at junctions is not complete and the numerical simulation result is in accord with the experimental result.