University of Twente Student Theses


Inline mixing of highly viscous sludge

Ebing, S.A.M. (2017) Inline mixing of highly viscous sludge.

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Abstract:After implementing a new process, Thermal Hydrolysis Process (THP), at the wastew­ater treatment plant (WWTP) in Hengelo, the mixing in the digester was not homo­geneous anymore. The goal of this research was to improve the inline mixing of three types of sludge in the pipeline entering the digester. Sludge behaves as a non-Newtonian fluid. Rheological measurements were performed on the different sludge types to determine the relation between the viscosity and shear rate, and to fit a non-Newtonian model. This was used as input in a CFD model made in ANSYS FLUENT of the relevant pipes to test the mixing of five different geometries. The k - E turbulence model was used together with the species transport and discrete model. The CFD model was validated using pressure measurements. The power law was chosen as non-Newtonian model and fitted on viscosity measure­ments performed by the TU Delft. The main conclusion of the CFD modelling was that a venturi with a diameter of 40 mm gave the best mixing results. However, when deter­mining the discretization error, the numerical solution appeared to be mesh dependent. This was likely caused by the sensitivity of the k - E model to disturbances which arose due to the turbulence generated by the venturi. Hence, validation on pressure did not fully succeed. A next step would be to choose a more suitable turbulence model and perform the simulations on a mesh with a higher resolution.
Item Type:Internship Report (Master)
Faculty:ET: Engineering Technology
Programme:Mechanical Engineering MSc (60439)
Keywords:CFD modelling, inline mixing, power law model, non-Newtonian, sludge, venturi
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