Experimentally Determined Solute Mixing under Laminar and Transitional Flows at Junctions in Water Distribution Systems

The water quality model in water distribution systems adopted in EPANET and other commercial simulation programs assumed perfect mixing of solute at pipe junctions. However, imperfect solute mixing at pipe junctions at turbulent flow has been reported. Yet, the mixing under laminar and transitional flow is rarely reported and thus is the focus of experimental study reported here. The experimental results show that the average Reynolds number and the outflows Reynolds number ratio controls degrees of the mixing at the pipe junctions. For cross junctions, the mixing degree is a function of the average Reynolds number in three regions; each has different mixing mechanisms and mathematical relationship. For double-Tee junctions, the dimensionless connecting pipe length plays a more important role than the Reynolds number ratios of outflows and average Reynolds number on mixing because a longer connecting pipe length gives more mixing space and time for the water flow mixing.

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