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UBC Theses and Dissertations

On the development of a method for continuous fractionation of non-Brownian particles in a viscoplastic fluid Shanb Ghazani, Mohammad


This study focuses on the mechanical fractionation of non-Brownian particles in layered yield stress fluids. We extend a novel principle outlined in a batchwise technique- which works based upon the difference in starting criteria for motion in a weak gel- and create a continuous separation in an annular gap undergoing the spiral Poiseuille flow. Experimental equipment is designed, constructed and operated to evaluate -continuously- the aforementioned fractionation idea. This work is presented in three different, yet complementary studies. In the first study, we performed a series of batchwise tests, in a centrifuge, to develop criteria for motion of the individual classes of particles of both monodisperse and bidisperse suspensions in layered fluids, and to determine the stability of this multilayer fluid undergoing centrifugation. We also examined the usefulness of this separation technique on three different suspensions related to the bio-product industry. In the second part, the design challenges of the continuous device were elaborated and the essential design elements were addressed. Next, the fully developed flow field inside the fractionator was analyzed and shown that not all the operating conditions result in stable operation. We found that there is a subset of all potential operating conditions in which this methodology will work and this critically depends upon rheology and radii of the multilayer fluid. We summarized our findings into a number of qualitative "rules of thumb" to run the device. In the last part of the work, we extended the work to a continuous methodology and demonstrated particle fractionation using both ideal and industrial particle suspensions. To benchmark our calibration curves, we examined and measured the critical force to initiate the motion for (monodisperse) spherical and fibre-shape particle suspensions and found that this critical force presents a similar trend to the batchwise test but at a lower threshold. A similar finding was found in the second test where we examined the separation of MFC. We argue that this is an anticipated result as the two geometries are in different stress states. Despite this, we were able to achieve a separation at the same trend as the batchwise methodology.

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