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Influence of underflow on sediment trapping efficiency: a) investigation by various authors b) model 1 numerical and physical model results
Source publication
A vortex settling basin (VSB) offers a promising alternative to conventional sediment settling structures, such as sand traps, for the removal of fine non-cohesive sediment for potable water use at small river abstraction works of less than 100 l/s pump capacity (7.2 Ml/d at 20 h/d). The hydraulic design of a suitable VSB was carried out by numeric...
Contexts in source publication
Context 1
... literature, no apparent trend could be observed from data undertaken by previous studies as shown in Figure 2a. Curi et al. (1979);Mashauri, (1986); Paul, (1988) underflow(Qu)/inflow(Qi) ratios were between 4% to 16%. ...
Context 2
... was investigated on model 1 summarized in Table 1 with only the underflow being varied. Figure 2b summarizes physical and numerical model results with different sediment particles: 75 µm, 100 µm and d50 = 112 µm. Having a ratio greater than 10% leads to air core formation decreasing trapping efficiency thus a ratio 5% to 10 % is recommended as to achieve maximum trapping efficiency with minimum water loss. ...
Citations
... They found the RSM to be reliable for optimizing the geometrical factors of a cyclone. Kiringu and Basson (2019) measured the sediment trapping efficiency of fine noncohesive sediment particles by a VSB at small river abstraction works of less than 100 L=s. They applied a Reynolds Stress Model to simulate the fluid-particle interaction in a commercial CFD software (FLUENT ANSYS version 19.1). ...
... Particle size had an influence percentage that was similar to that of Q in on trapping, which means a coarse gradation is better trapped inside a VSB and then deposited on the floor and washed out through the orifice. The importance of d s on trapping efficiency was also indicated in Kiringu and Basson (2019). The experiment with 0.3625-mm particle diameter, 0.07-m orifice diameter, 0.1-m end sill, 8-L=s inlet flow rate, and 0.05-m outlet weir showed the highest η o . ...
In this study, the performance of a vortex settling basin (VSB) with a clockwise circulation was experimentally evaluated. The inlet flow rate was in the range of 8–22 L/s. Based on the Taguchi and response surface methods, the effects of inlet flow (Qin), central orifice diameter (do), sediment particle diameter (ds), end sill height (Sout), and outlet weir height (W) were investigated. The orthogonal array, signal-to-noise ratio (SNR), and ANOVA were used to study the performance of the VSB. The inlet canal efficiency, trapping efficiency, water abstraction ratio, and total performance were measured and the SNR calculated. The total performance of the VSB was calculated based on the inlet canal efficiency, trapping efficiency, and water abstraction ratio. The factors Qin, W, Sout, do, and ds were ranked first to fifth with respect to impact on total performance. Based on dimensional analysis and experimental data analysis, total performance receives direct influence from Qout/Qin while being inversely affected by Sout/Hin, W/Hin, and do/Hin. The highest total performance was obtained for Sout/Hin=0.265, W/Hin=0.159, Qout/Qin =0.915, D50/Hin=0.0019, and do/Hin=0.370.
... Extensive numerical and physical modelling was undertaken at Stellenbosch University laboratory investigating the removal of fine-non cohesive sediment by VSB at small abstraction works (Kiringu and Basson, 2019). The parameters varied are summarized in Appendix J Figure J-1 and the findings from this study are summarized below: a) Gravity is the primary driver in sediment removal with centrifugal forces assisting in keeping the particles longer in suspension. ...
... Extensive numerical and physical modelling was undertaken at Stellenbosch University laboratory investigating the removal of fine-non cohesive sediment by VSB at small abstraction works (Kiringu and Basson, 2019). The parameters varied are summarized in Appendix J Figure J-1 and the findings from this study are summarized below: a) Gravity is the primary driver in sediment removal with centrifugal forces assisting in keeping the particles longer in suspension. ...
Executive Summary More than a decade ago, a SA Water Research Commission (WRC) study was completed by Stellenbosch University and guidelines were generated for the hydraulic design of river abstraction works: "Considerations for the Design of River Abstraction Works in South Africa" (Basson, 2006). The guidelines have been used in the designs of many of the new abstraction works in Southern Africa since 2006 and this is probably one of the research success stories of the WRC. The guidelines of this report update the 2006 technology and also include additional components to make the designs even more sustainable. The "Design Guidelines of River Abstractions/Diversion works for Potable water use, Irrigation and Hydropower Generation in South Africa" consist of three volumes as summarised below. Volume 1: Design Guidelines and typical Hydraulic Designs of small to large River Abstractions/Diversion works The hydraulic design guidelines for small potable river abstraction works (pump capacity < 100 l/s; 8.6 ML/d) discussed in this report aim to provide sustainable, relatively low capital and low operation cost solutions, which are robust and suitable for the South African semi-arid climate with extremes of droughts and floods. The recommendations made in these guidelines are based on experience, and a combination of hydrodynamic numeral and hydraulic physical modelling. Hydraulic design guidelines were also developed for medium and large river abstraction/diversion works, with and without weirs. Medium sized abstraction works (100 l/s to 1000 l/s; 8.6 ML/d to 86.4 ML/d@24h/d) should typically have a weir and gravel trap, with pump canals as settlers or a hopper and jetpump for sediment control. Large abstraction works (pump capacity > 1000 l/s; 86.4 ML/d), could typically have a weir, boulder trap, gravel trap and pump canals/settlers for sediment control, or if a weir is not needed or not feasible, then a high intake wall and wing wall is proposed, with a submerged intake and trashrack, with a hopper and jetpump for sediment control. The site selection of river abstraction/diversion works and site inspection at a river bend is discussed in detail, with considerations for calculating the hydrology and what to specify for the topographical survey. The guidelines also deal with mechanical equipment, pipework, construction, maintenance and operational and environmental considerations. With the correct hydraulic design to overcome sedimentation problems, operational and maintenance problems could be minimized for sustainable development of river abstraction/diversion works. Design guidelines are provided for sediment traps such as sand traps, settlers and vortex settling basins. Volume 2: Case Studies of River Abstractions/Diversion works Since the University of Stellenbosch have been involved in the design and model studies of a number of river abstraction works with consultants over the years, three of these have been selected as case studies for this investigation to illustrate the design development of river abstraction/diversion works based on the above referred WRC guidelines. For the purpose of evaluating the performance of existing river abstraction/diversion schemes, of which some are designed according the above referred WRC guidelines, four case studies have been selected for this investigation. Field measurements have been performed on the Design of sustainable river abstractions/diversion works for potable water use and irrigation in South Africa March 2020 Page ii different components/aspects of these schemes (such as the location of the works on the river, orientation of the works, the weir, a boulder trap, a gravel trap, pump canal sedimentation, intake trashrack, debris, pump types and operating problems) of these case studies and feedback on performance from operators of some of these have been obtained by means of questionnaires. Guidelines for the hydraulic design of sediment management components at hydropower dams and at hydropower river diversions are provided in this report. The guidelines are based on a literature review, engineering design experience, physical and mathematical modelling. This report investigates the hydraulic design requirements of low level outlets at dams located underneath HPP intakes, for the control of sedimentation near the intakes to prevent non-cohesive sediments entering the turbines, by using pressure flushing and/or free flow water level drawdown flushing if sufficient excess flow is available. Guidelines for hydro-power plant diversion design in run-of-river schemes were prepared by literature review of the hydraulic design, sediment and debris management requirements. A new river diversion design was proposed for SA conditions with a weir (uncontrolled or controlled with gates or inflatable), a boulder trap, high intake wall with a submerged intake, gravel trap, trash racks, high-velocity canals with flow control gates, followed by a sand trap.
The aim of the paper was to analyze the separation process of solid-liquid systems in designed and constructed modified swirl sedimentation tanks. The analysis process included a series of experimental tests performed using model research materials, such as water and quartz grains with different diameter. An attempt was made to determine the correlation between the process parameters, structural elements, and the obtained efficiency of the separation process. The obtained data allowed for the broadening of knowledge concerning the phenomenon of sedimentation and swirling, as well as the principle of operation of rainwater separators. The aim of the research was to enable a more precise selection of separators according to the conditions in which they are meant to fulfill their function. The achieved results are a motivation for, and justify, further research concerning the design and operation of such devices.
