Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems

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 co...

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Autores principales:	Marek Sokáč, Yvetta Velísková
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	longitudinal dispersion sewer pipes sediments dead zones Reynolds number Hydraulic engineering TC1-978 Water supply for domestic and industrial purposes TD201-500
Acceso en línea:	https://doaj.org/article/47d1751f7d824bf88f60d8fa5e9e38f4
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id	oai:doaj.org-article:47d1751f7d824bf88f60d8fa5e9e38f4
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spelling	oai:doaj.org-article:47d1751f7d824bf88f60d8fa5e9e38f42021-11-25T19:14:59ZImpact of Sediment Layer on Longitudinal Dispersion in Sewer Systems10.3390/w132231682073-4441https://doaj.org/article/47d1751f7d824bf88f60d8fa5e9e38f42021-11-01T00:00:00Zhttps://www.mdpi.com/2073-4441/13/22/3168https://doaj.org/toc/2073-4441Experiments 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<sup>−3</sup> m<sup>3</sup>·s<sup>−1</sup>, 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 D<sub>x</sub> 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.Marek SokáčYvetta VelískováMDPI AGarticlelongitudinal dispersionsewer pipessedimentsdead zonesReynolds numberHydraulic engineeringTC1-978Water supply for domestic and industrial purposesTD201-500ENWater, Vol 13, Iss 3168, p 3168 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	longitudinal dispersion sewer pipes sediments dead zones Reynolds number Hydraulic engineering TC1-978 Water supply for domestic and industrial purposes TD201-500
spellingShingle	longitudinal dispersion sewer pipes sediments dead zones Reynolds number Hydraulic engineering TC1-978 Water supply for domestic and industrial purposes TD201-500 Marek Sokáč Yvetta Velísková Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems
description	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<sup>−3</sup> m<sup>3</sup>·s<sup>−1</sup>, 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 D<sub>x</sub> 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.
format	article
author	Marek Sokáč Yvetta Velísková
author_facet	Marek Sokáč Yvetta Velísková
author_sort	Marek Sokáč
title	Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems
title_short	Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems
title_full	Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems
title_fullStr	Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems
title_full_unstemmed	Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems
title_sort	impact of sediment layer on longitudinal dispersion in sewer systems
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/47d1751f7d824bf88f60d8fa5e9e38f4
work_keys_str_mv	AT mareksokac impactofsedimentlayeronlongitudinaldispersioninsewersystems AT yvettaveliskova impactofsedimentlayeronlongitudinaldispersioninsewersystems
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Impact of Sediment Layer on Longitudinal Dispersion in Sewer Systems

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