Neal, Grace (2012)
M.Res. thesis, University of Birmingham.
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By adapting the techniques Planar Laser Induced fluorescence (PLIF) and Particle Image Velocimetry (PIV) for a transient system with a rising free surface the mixing that occurs as a vessel is filled process has been investigated.
The PLIF technique has been demonstrated to give good repeatability for the same flow conditions and qualitative examination of the images has revealed a change in the mixing mechanism from laminar to turbulent above a critical value of the Reynolds number (Re~1000), with cases above this reaching a log variance of -2 which equates to 92% mixed. PIV allowed the distribution of momentum and shear in the tank to be investigated, highlighting dead regions in the bottom corners of the tank and showing the top half of the tank was relatively quiescent. To improve the mixing performance, changes to the flow rate and the nozzle design were made to increase the movement in these regions.
Sinusoidal variations in the inlet velocity increased the level of mixing from an unmixed state so that the vessel reached 84% mixed. With a swirl insert in the end of the nozzle the level of mixing in the tank reached 95% (log variance of -2.6) at one point in the fill. Combining these improvements may produce a more sustained and reliable improvement and should feature in any future work.
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