UBC Theses and Dissertations
Particle impingement onto a moving substrate Roberts, Justin Jennings
Particle sprays are salient in processes such as erosion in turbomachinery and traction enhancement in the railroad industry. In this study, particles with a Stokes number at the nozzle much larger than unity were sprayed at an acute angle between a horizontal, flat, moving substrate, representing the rail, and a wheel. A device was created that contained a sprayer aimed between the wheel and moving substrate, with the rim of the wheel hovering above the flat substrate. The particles form a spray into the nip that can ricochet between both the wheel and substrate. The standard deviation of the angle that the particle trajectories make as they exit the nozzle can be used to describe the geometry of the spray. Similarly, the normal and tangential coefficients of restitution describe ricochet effects by quantifying the amount of energy dissipated through the particle-substrate interaction. Initial work in this study focuses on the spray and bounce properties to determine their correlation to the particle’s efficiency, which was defined as the percentage of particles leaving the nozzle that make it into the nip. Next, the effects of shape and size were determined using particles with similar compositions. Then, the effect of coating the particles and substrate speed was determined. For silica sand with diameters from 0.2-0.6 mm, the typical efficiency was 68% with a flat wheel and rail profile. The larger and rounder particles were found to deposit the best, with coated sand having an efficiency of 91%. It was discovered that the improvement in the efficiencies may be from reducing the spread of the particle spray from the nozzle from 8° to 3°, which increased the likelihood that the particles make it between the wheel and belt. Lastly, decreasing the substrate speed below 18 km/h produced lower efficiencies due to the particle-particle interactions as they approach the wheel-substrate interface unless the mass flowrate of the particles was reduced.
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