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Studies of fluidic systems for environmental applications

Egarr, Darrell A. 2005. Studies of fluidic systems for environmental applications. PhD Thesis, Cardiff University.

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A Hydrodynamic Vortex Separator (HDVS) is a form of Combined Sewer Overflow (CSO) used for solid-liquid separation. HDVSs are also used at sewage treatment works for the separation of grits that are transported through the sewer network. The residence time of the fluid that passes through these devices is increased by the rotational nature of the flow and hence, the time that gravity has to act on particulates is also increased. This feature of the fluid dynamics means that a HDVS may also be used as a contact vessel for disinfection of wastewater during a CSO event. To date the physics of these systems is not completely understood in terms of particulate separation. To achieve a greater understanding of the HDVS an initial sensitivity study using Computational Fluid Dynamics (CFD) was carried out looking at factors that may influence the efficiency and to gain an insight into variables that should be accounted for during experimentation and test rig design. Following this sensitivity study a 0.75m diameter HDVS was studied under laboratory conditions where it was found that a parameter described as the particle surface load controls the efficiency of the HDVS and not the particle settling velocity as previously thought. A model was developed to describe the retention efficiency and was also applied to scaling. However, more work is required to achieve a greater understanding of the application of the retention efficiency model to larger separators. Experimental trials on a 3.4m diameter HDVS were undertaken and from this it was found that the most suitable residence time distribution model for a HDVS is the axial dispersion model. Attempts to use CFD to model the separation efficiency of such systems have to date failed. However, validations of the residence time characteristics are reasonable. This has allowed CFD to be used to study the application of residence time to disinfection where it has been shown that an existing disinfection model may be developed to describe the disinfection performance of a HDVS. Scaling laws have also been developed using CFD for the residence time and CFD has consequently given an insight into the fluid dynamics within the HDVS.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Engineering
Subjects: T Technology > TD Environmental technology. Sanitary engineering
ISBN: 9781303209987
Funders: EPSRC, Hydro International PLC
Date of First Compliant Deposit: 30 March 2016
Last Modified: 08 Sep 2022 12:56

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