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Article

Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems

Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 84104 Bratislava, Slovakia
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Academic Editors: Xing Fang, Jiangyong Hu and Suresh Sharma
Water 2021, 13(22), 3168; https://doi.org/10.3390/w13223168
Received: 28 September 2021 / Revised: 25 October 2021 / Accepted: 2 November 2021 / Published: 10 November 2021
(This article belongs to the Special Issue Water Quality Modeling and Monitoring)
Experiments focused on pollution transport and dispersion phenomena in conditions of low flow (low water depth and velocities) in sewers with bed sediment and deposits are presented. Such conditions occur very often in sewer pipes during dry weather flows. Experiments were performed in laboratory conditions. To simulate real hydraulic conditions in sewer pipes, sand of fraction 0.6–1.2 mm was placed on the bottom of the pipe. In total, we performed 23 experiments with 4 different thicknesses of sand sediment layers. The first scenario is without sediment, the second is with sediment filling 3.4% of the pipe diameter (sediment layer thickness = 8.5 mm), the third scenario represents sediment filling 10% of the pipe diameter (sediment layer thickness = 25 mm) and sediment fills 14% of the pipe diameter (sediment layer thickness = 35 mm) in the last scenario. For each thickness of the sediment layer, a set of tracer experiments with different flow rates was performed. The discharge ranges were from (0.14–2.5)·10−3 m3·s−1, corresponding to the range of Reynolds number 500–18,000. Results show that in the hydraulic conditions of a circular sewer pipe with the occurrence of sediment and deposits, the value of the longitudinal dispersion coefficient Dx decreases almost linearly with decrease of the flow rate (also with Reynolds number) to a certain limit (inflexion point), which is individual for each particular sediment thickness. Below this limit the value of the dispersion coefficient starts to rise again, together with increasing asymmetricity of the concentration distribution in time, caused by transient (dead) storage zones. View Full-Text
Keywords: longitudinal dispersion; sewer pipes; sediments; dead zones; Reynolds number longitudinal dispersion; sewer pipes; sediments; dead zones; Reynolds number
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MDPI and ACS Style

Sokáč, M.; Velísková, Y. Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems. Water 2021, 13, 3168. https://doi.org/10.3390/w13223168

AMA Style

Sokáč M, Velísková Y. Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems. Water. 2021; 13(22):3168. https://doi.org/10.3390/w13223168

Chicago/Turabian Style

Sokáč, Marek, and Yvetta Velísková. 2021. "Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems" Water 13, no. 22: 3168. https://doi.org/10.3390/w13223168

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