Modelling Transport of Non-Spherical Particles in Small Channel Flow

• Main Author: Holmstedt, Elise
• Format: Doctoral Thesis
• Language: English
• Published: Luleå tekniska universitet, Strömningslära och experimentell mekanik 2016
• Subjects: Fluid Mechanics and Acoustics; Strömningsmekanik och akustik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60402; http://nbn-resolving.de/urn:isbn:978-91-7583-765-9; http://nbn-resolving.de/urn:isbn:978-91-7583-766-6

A model has been developed to predict the movement of oblate and prolate particles on amicro- and nano-scale in laminar channel flow, both for purposes of statistical aggregationand to study motion of single particles. For the purpose of this thesis the model has beenadapted to examine particle deposition patterns in the human lung and the filtration ofparticles during manufacturing of composites, but the possibilities of the model extendto all areas where the particle Stokes and Reynolds numbers are small.To examine the influence the breathing pattern has on the deposition of inhalednano- and micro-fibres deposition rates were compared at different injection points ofthe breathing cycle, where maximum deposition was found when the particles releasedat the beginning of the respiratory cycle while minimum deposition occurred when therelease came at peak inhalation. A comparison between a quasi-steady flow and a cyclicflow was done and it was found that a quasi-steady solution provides a reasonably goodapproximation if the velocity used is a mean of the velocity during the residence time ofthe simulations.A statistical study was done to compare the deposition rates of oblate and prolateparticles of different size and aspect ratio as they travel down narrowing bronchi in asteady, fully developed parabolic flow field. The model shows a clear correlation betweenincreased particle size and increased deposition, it also consistently yielded a higherdeposition rate for oblate particles compared to prolate particles with a similar geometricdiameter. A study of the motion and orientation of single oblate and prolate particleswith large aspect ratio and the same geometric diameter has also been done.In liquid moulding of fibre reinforced composites the resin can be enhanced by nanoandmicro-particles to give the final product additional properties. This is a processthat can be simulated by approximating the gap formed between the fibre bundles to achannel flow with a radially suctioning component caused by the capillary pressure in themicro channels in the bundles. First this flow field is described with a radial componentthat is constant over the length of the channel and compared with a flow purely drivenby an applied pressure gradient without radial forces. Particle size showed a small butstill noticeable influence, particularly for larger particles under the influence of gravity.The second flow field used is time dependent where the flow front in the bundlesand channel mimics that of previous observations. There is initially a period where theflow front in the channel is leading but the radial capillary fluid transport causes thisto retreat and be overtaken by the flow front in the bundles. Particles mixed in theresin will in general travel with a velocity greater than that of the fluid front until theradial velocity component at that point filters the particles by transporting them to thechannel wall. Particle geometry has a smaller impact on the deposition rates in compositemanufacturing than in inhalation since the effect of Brownian forces and gravity are muchsmaller, although there is still some discernible patterns such as a higher deposition ratefor spherical particles during the transport to the flow front.