Modelling transport of non-spherical particles in laminar flow

Abstract: A model has been developed that can be used to predict the transport of non-spherical particles in the nano- and micro scale range for different applications. This may be the flow in the lungs or flow taking place during composites manufacturing, but the model can be applied to many applications where the particle Stokes and Reynolds numbers are small. The model can, for instance, be used to simulate an evenly random distribution of particles and then follow them through a laminar flow in a straight circular tube, either to study the statistical congregation of multiple particles or to follow the path of an individual particle. Both gravitational settling and Brownian motions are included in the model and their influence was also examined. To increase the understanding of the influence of the breathing pattern on the deposition of inhaled nano- and micro-fibres simulations were done in a straight model airway. Maximum deposition rate was found when particles were released in the beginning of the respiratory cycle while a minimum when the release came at the peak of inhalation. A comparison was done of a cyclic flow field and a quasi-steady one to see if the latter could accurately be used to replace the former. A quasi-steady solution generally provides a relatively good approximation to cyclic flow if an average velocity over one residence time of the particles moving with the mean fluid velocity is used. A statistical study was done to compare the deposition rates of oblate and prolate particles of different size and aspect ratio as they travel down narrowing bronchi in a steady, fully developed parabolic flow field. The model shows a clear correlation between increased particle size and increased deposition, it also consistently yielded a higher deposition rate for oblate particles compared to prolate particles with a similar geometric diameter. A study of the motion and orientation of single oblate and prolate particles with large aspect ratio and the same geometric diameter has also been done. To see the effect the different forces have on the particle it was first studied with only the force of the flow field acting on it. Clear Jeffery orbits were visible in the simulations, although the periods of the orbits were shorter for the oblate particles than the prolate ones. When Brownian motion was introduced the motion of the particles became less periodic. For prolate particles Jeffery orbits could still be distinguished, unlike for the oblate particles whose movements mostly resembled random tumbling. In some methods to produce fibre reinforced polymer composites a fabric is impregnated with a fluid that may contain particles on the micro- and nano scales. These particles are aimed to give the final product additional properties. It is therefore interesting to be able to reveal how the distribution and orientation of such particles are affected by the processing condition. During the manufacturing of the fabric and during the subsequent lay-up in a mold relatively large channels are formed between bundles offibres where the impregnating fluid flows; there is also micro channels within the bundle that are also impregnated by the fluid and the capillary action there may be modelled as a suctioning force on the walls of the channels. Therefore in this study the channel between the bundles are represented as a tube with a circular diameter and a flow field that are being sucked to the sides as it travels down the tube. A random distribution of particles is introduced at the inlet of the channel and the deposition is studied and the results are compared to a case when the flow is purely driven by an applied pressure gradient without any suction on the walls.