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Numerical Simulation of Particle Motion in Microchannel Flows
The major goal of the present study is to investigate the particle dynamics in a microchannel flow. The microchannel is composed by two parallel plates separated by a distance of 80μm. There is a spline-shaped obstacle attached on the lower wall of the channel with height of 40μm and 60μm. The carrier fluid are chosen to be air and slurry used in the CMP process. The flow inside the channel is assumed to be laminar and satisfies the continuum assumption. The motions of SiO2 and Cu particles, with diameters ranging from 0.5nm to 5μm, are to be studied in this flow field. The flow field is solved by finite element method, while the particle trajectories are obtained by integrating their equation of motion.
Due to the order of magnitude of forces acting on particle depend on the properties of particle and fluid such as particle diameter, density, and particle Knudsen number, the characteristics of particle motion in gaseous and liquid flow fields is fundamentally different. Due to large density ratio between particle and fluid, the dominant force of particle motion in air flow are drag and Brownian motion. For large particles, it is found that drag controls the motion of particles causing particle impingement on the walls and obstacle. For particle with diameters of order of 1nm, it is found that the effect of Brownian motion on particle motion becomes significant and particles have the chance to impinge on the walls.
In slurry flow field, gravity, pressure gradient force, and virtual mass force need to be included in the equation of particle motion in addition to drag force due to comparable densities between particle and fluid. For large particles, it is found that particle has the chance to be trapped into the recirculation zone behind the obstacle. However, the small particles exhibit the trajectories following closely with fluid motion.
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