Search

Sewage pumping stations represent an element of the sewer system, which is directly responsible for affecting serviceability; i.e., failing pumps may result in combined sewer overflows or flooding. However, failures of sewage pumps are not yet incorporated in sewer assessments due to lack of data. This paper presents the analysis of pump failure data provided by two sewer management authorities in The Netherlands. Pump failures have been studied accounting for the nature of the failures, the operation and maintenance procedures of the management authority, the aging of the pumps, and the changes in the environment of pumps. The analysis shows that sewage pumps fail relatively often due to the composition of sewage and the discontinuous operation of the pumps. The interarrival time and the duration of failures are highly variable and independent of the specific function of the pump. Resulting pump failure characteristics are applied in a Monte Carlo simulation to calculate the impact of failures on combined sewer overflow volumes. The results indicate that the serviceability of sewer systems is significantly affected by tailing pumps. Therefore, including pump availability in sewer system assessments should be considered. CE Database subject headings: Sewers; Pumps; Statistics; Sewage.

Urban runoff remobilises solids and their associated pollutants from urban-built environments and transports them to drainage systems via gully pots. This study presents an extensive monitoring campaign on the solids loading to drainage systems, including 104 gully pots as sampling locations and lasting 2 years. The solids loading is modelled with Build-Up and Wash-Off (BUWO) models and a Regression Tree (RT). The performance of the RT is substantially better than the performance of the BUWO models, such that it is not recommended to use a single BUWO model to predict the loading of a set of gully pots/catchments. It is discussed whether the generally observed mismatch between monitoring data and wash-off models, both in this study and in literature, points to a fundamental misunderstanding of the underlying processes. Finally, the results show that an increased street sweeping frequency does not significantly reduce the solids loading to drainage systems. [ABSTRACT FROM AUTHOR]

Transition from laminar to turbulent flow of non-Newtonian fluids is investigated using velocimetry data. These data are obtained by applying particle image velocimetry to images obtained through ultrasound imaging (echography). This yielded the observation of intermittent structures (puffs and slugs) that are formed during transition. Post its observation, transition is characterized using the friction factor curves and turbulence intensity. Further, a number of models used to predict transition are assessed. This showed the Reynolds number based model by Slatter and the stability parameter based model by Hanks to be most suitable for non-Newtonian fluids with yield stress and low behaviour index. [ABSTRACT FROM AUTHOR]

This article concerns the turbulent flow of Herschel–Bulkley slurries through circular horizontal pipes; in particular, that of concentrated domestic slurry obtained upon separation of domestic waste water and reduction in the use of water for domestic purposes. Experiments with a rheologically equivalent clay (kaolin) slurry indicated a non-Newtonian behaviour of the Herschel–Bulkley type. A modified wall function was developed to enable the Reynolds-averaged Navier–Stokes simulation of Herschel–Bulkley slurries to estimate the wall shear stress. Despite the accuracy achieved, the use of Reynolds-averaged Navier–Stokes models for an entire waste water system is impractical. Therefore, this article assesses the accuracy of semi-empirical models in estimating frictional losses. It also discusses possible modifications of existing models to encompass Herschel–Bulkley behaviour. An evaluation suggests that most existing models deliver estimates of comparable accuracy; however, the probability of these estimates being reliable, while accounting for experimental errors in quantifying the actual frictional losses, is rather low. [ABSTRACT FROM AUTHOR]

In order to analyse the flow characteristics of free-surface vortexes and to validate the Burgers vortex model by using stereo particle image velocimetry, experiments are conducted in a 600 mm diameter vortex tank. Measured axial velocities indicate that 10–25% of the flow is transported through the vortex core. The velocity profiles show that the axial flow is concentrated in a domain bounded by two times the core radius. Despite Burgers' assumption of radially independent axial velocity profiles, the model quantifies the tangential velocity profile within a relative uncertainty of circa 10%. The measurements show that it seems valid to use Burgers' model to obtain an estimate for the core radius by taking the average axial velocity over a radial domain of approximately 2.2 times the core radius. The Burgers model quantifies the air core depth with an uncertainty of 20% relative to the measurements. When compared with the magnitude of vorticity diffusion by molecular viscosity, the experiments show that there is no significant diffusion by radial turbulence. [ABSTRACT FROM AUTHOR]