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UBC Theses and Dissertations

Reducing variabilities in the mixer inflow concentration Soltanzadeh, Ali


The thesis focuses on mixing fluids, and it has three main parts. The first part investigates mixing in agitated pulp chests. A new model for identifying the performance of mixing in the pulp chest is developed. This newly developed model simplifies the previous pulp chest model and successfully describes non-ideal flow behavior, including channeling and dead-zones which occurs in the agitated pulp chests. The model is verified through experimental data obtained in a laboratory-scale agitated pulp chest. In the second part of the thesis, a novel method for identifying residence time (the average time that it takes for material to exit the mixer) from input and output data is developed. The main benefit of this new method is that it does not require that an individual have prior knowledge of the process to evaluate the mixing inside the flow system. The same idea is used to estimate the higher moments of linear time invariant transfer functions from a batch of input and output data. The ability to estimate higher moments of a transfer function enables one to reconstruct the original transfer function without having knowledge of its structure. This opens new possibilities in non-parametric system identification and residence-time theory. It is also shown how a bound on the delay of all pole transfer functions can be found using the first and second moments. In the third part of the thesis, a new class of mixers is designed. These mixers do not have agitators, yet they are as effective as stirred tanks in reducing fluctuations in their inlet stream. However, they are only effective for reducing the concentration fluctuations in the flow direction (axial mixing). This design splits the fluid into different channels and recombines these streams to achieve mixing. These mixers are especially useful in microfluidic applications where there is a physical limitation in using agitators for mixing; therefore, in the final section of the thesis, a mixer is designed and its geometry is calculated for microfluidic purposes. Moreover, the effectiveness of the mixer in reducing inlet concentration fluctuations is shown through computational fluid dynamic simulations (CFD).

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