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Physical and numerical modelling of 3-D flow and mixing processes in contact tanks

Rauen, William Bonino 2005. Physical and numerical modelling of 3-D flow and mixing processes in contact tanks. PhD Thesis, Cardiff University.

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The flow pattern in contact tanks (CTs) can exhibit complex hydrodynamic and mixing processes, typically with the occurrence of recirculating flow and dead zones, shear and wall generated turbulence, as well as regions with relatively low horizontal velocities and others with fairly high vertical accelerations. The characterisation of these phenomena is of paramount importance for an integrative understanding of their effects on the performance of CTs, demanding the use of sophisticated investigative techniques, such as the direct assessment of the velocity field and use of appropriate and refined numerical schemes. Nonetheless, thorough comparisons of the performance of CTs against the predictions of complex three-dimensional (3-D) numerical hydrodynamic and solute transport models have yet to be reported. A physical and numerical investigation of the 3-D hydrodynamic and mixing processes in contact tanks was undertaken in this study. Physical experimentation has been carried out for various configurations of a prototype CT, providing data for the validation of numerical model results. These included velocity measurements with an Acoustic Doppler Velocimeter, as well as assessments of solute transport processes by using tracer techniques. A 3-D Computational Fluid Dynamics model has been developed, based on the finite volumes method and using a low Reynolds number k-s turbulence model, in addition to a depth-averaged eddy viscosity approach. The Reynolds-averaged Navier-Stokes equations have been discretised using the SIMPLER algorithm and solved in a line-by-line fashion for a non-uniform mesh configuration. The parameter C^ for the k-s model has been calculated as a function of local turbulence quantities. A sensitivity analysis of the predicted results has been undertaken for the variation of the Schmidt number and type of turbulence model. The numerical model predictions have been validated against analytical and empirical results for benchmark flow problems, as well as for hydrodynamic and solute transport data from various prototype CTs. An encouraging agreement has been observed between the data and corresponding numerical model predictions.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Engineering
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
ISBN: 9781303201479
Date of First Compliant Deposit: 30 March 2016
Last Modified: 10 Jan 2018 04:26

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