Experimental Study Of Soulte Mixing At Double-T Junctions In Water Supply Systems

Recent studies focused on the mixing behavior at cross junctions, nevertheless, the research results on mixing at other junction configurations, such as double-Tee junctions, were insufficient. The experimental results show that an incomplete mixing behavior at double-Tee junctions and the mixing is better than that at the cross junctions. Double-Tee junctions can potentially be misrepresented as cross junctions because of network skeletonization. Hence, the diffusion and dilution of the contaminants at junctions were largely misestimated. To precisely predict the diffusion of chemical or malevolent contamination in the water supply systems and build a high accuracy water quality model, the mixing behavior at double-Tee junctions should be lucubrated systematically. To examine the mixing phenomenon and collect accurate mixing data at the double-Tee junction, a series of laboratory experiments were carried out:Firstly, the distorted similarity theory was introduced, and the physical model of the joint was assembled based on the Euler criterion and Reynolds criterion. The values of Reynolds number (Re) in these experiments are all between10000and50000.Secondly, we introduce photography as tool to examine the mixing phenomenon at the double-Tee joints in a visualized way. Many kinds of experiments have been visualized, including laminar flow and turbulent flow at all pipes, various Re at inlets and various Re at outlets. The visualized results indicate that the mixing at the double-Tee joints in laminar flow condition is better than that in the turbulent flow condition, when the dimensionless connecting pipe lengths (LID) is small. When the Reynolds number ratio of inlet is greater than1(ReW/ReS>1), there is a more complete mixing at the joint. Similarly, when the Reynolds number ratio of outlet is smaller than1(ReN/ReE<1), indicating a better mixing.Thirdly, the laboratory experiments were carried out with various Reynolds number ratios at the inlets (ReW/ReS) and outlets (ReN/lReE<1) combined with different LID. Results showed that the L/D and ReW/ReS served an important function in the mixing at double-Tee junctions, however, Reynolds number ratios at the outlets showed a less important in mixing. Afterwards, a conceptual model with the dimensionless parameter φ that described the mixing behavior at double-Tee junctions was improved. Finally, we study the different pipe diameter ratios (DW/DS) that effect on the mixing at double-T junctions. The results indicated that the double-Tee joints 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 keep the same. This is due to the entering flows at the pipe joint with a large size difference has sufficient time and space to interact and diffuse in the connecting segment of the joint configuration. At last, the contour map of the mixability were obtained, the mixing result at the double-T junctions can be calculated by interpolating in the contour map.