Prof. Arun Ramachandran 416-978-4162, United States
Abstract: Yield stress, τy, is a key rheological feature in many complex fluids, and it represents a critical stress demarcating the solid-like and liquid-behaviour in materials. It has been shown for particle suspensions that τy is a function of the weight fraction of the solid particles, X%, and a relationship between τy and X% could be useful for the determination of X% through τy. The measurement of τy and X% finds wide applications such as Clark’s hot water extraction used in Canada’s oil industry. Bitumen oil is recovered by slurring oil sands found in Athabasca with hot water and gas, and separating the oil attached to gas bubbles from clay particles using gravity settling. The settling tank consists of a middle and a bottom section based on the size of the particles, called middlings and tailings, which have an X% varying between 10 to 21% and 30 to 40%, respectively, with a trace amount of bitumen. Both fractions possess a small, finite yield stress as low as 10-4 Pa to 10 Pa, which is a function of X%. Occasional rise in X% can lead to sludging inside the extractor, mitigating the recovery of bitumen. Thus, determining τy and X% is of significance for early prediction of sludging. In this presentation, we focus on an inexpensive microfluidic technique to measure τy between 1 mPa to 10 Pa, and X% of clay suspension. We developed the theoretical framework with carbopol gel as a model yield stress fluid, and validated the technique using simulations in COMSOL® Multiphysics. We measured τy of cloisite clay suspension for a range of X% between 3 to 6%, and used the polynomial relationship between them to predict X% of the other samples of clay through the measurement of τy. We have demonstrated the ability of the microfluidic platform to accurately measure τy of suspension in-line for 15 min at various flow rates. Currently, we are working on measuring the yield stress of more representative samples of middlings and tailings such as kaolinite suspension, and actual samples from industry.
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