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Characterization of Mixing in a Simple Paddle Mixer



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Characterization of Mixing in a Simple Paddle Mixer Using Experimentally Derived Velocity Fields Douglas Bohl1 Naratip Santitissadeekorn2 Akshey Mehta1 and Erik Bollt2 Department of Mechanical and Aeronautical Engineering 2 Department of Mathematics Clarkson University Potsdam NY 1 Abstract The flow field in a cylindrical container driven by a flat bladed impeller was investigated using Particle Image Velocimetry PIV Three Reynolds numbers 0 02 8 108 were investigated for different impeller locations within the cylinder The results showed that vortices were formed at the tips of the blades and rotated with the blades As the blades were placed closer to the wall the vortices interacted with the induced boundary layer on the wall to enhance both regions of vorticity Finite Time Lyapunov Exponents FTLE were used to determine the Lagrangian Coherent Structure LCS fields for the flow These structures highlighted the regions where mixing occurred as well as barriers to fluid transport Mixing was estimated using zero mass particles convected by numeric integration of the experimentally derived velocity fields The mixing data confirmed the location of high mixing regions and barriers shown by the LCS analysis The results indicated that mixing was enhanced within the region described by the blade motion as the blade was positioned closed to the cylinder wall The mixing average within the entire tank was found to be largely independent of the blade location and flow Reynolds number I Introduction I 1 Background Mixing is a fundamental process in many natural and industrial flow fields In flows such as the current one under investigation i e highly viscous low speed flows 1 small scale motions are not available and mixing is a result of large scale motion in the flow Batch mixers similar to food mixers are a primary method for the processing of many materials However there are inherent drawbacks to a batch mixing process e g inconsistent mixture quality residual voids and



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