Particle deposition in industrial duct bends

Workplace illnesses result from exposure to harmful contaminants. Local exhaust systems can reduce these exposures and prevent the onset of disabling illnesses. Although extensive procedures aid engineers when designing these systems, particles that deposit in ducts can reduce the effectiveness of local exhaust systems and place workers at undue risk.; This work seeks to develop a model to estimate particle deposition in bends of an exhaust system. To accomplish this goal, a new method was developed to measure particle deposition by size in exhaust ducts at conditions typical of industry. While previous methods are limited to relatively small particles, small diameter ducts, and low Reynolds numbers, the new method enables measurement of particle deposition by size in any part or assemblage of parts of an exhaust system. Moreover, this method is adaptable to laboratory or field settings.; Using this new method, a factorial experiment examined particle deposition in full-size, industrial, duct bends. These experiments identified that models previously published under-represent drag force and over-estimate deposition when particle motion is outside the Stokes regime. Further, small but significant differences in particle deposition occur with changes in bend orientation. Particle penetration was not a multiplicative function of bend angle as theory predicts, due to the developing nature of turbulent flow in bends.; A new model was developed using the experimental data above to describe particle deposition by size in 90° bends of industrial ducts. This new model accounts for non-Stokes particle motion and for variable deposition patterns as a function of particle Stokes number. Whereas previous models fit the data poorly, r2 less than 30%, the new model explains 86% of the variability associated with the data.; The goal of this work was realized; the new model allows estimation of particle deposition by size in bends of industrial ducts. The methods developed here can be used to investigate other parts of a duct system, such as expansions and tees. Ultimately, these studies should enable engineers to avoid compromised exhaust systems due to deposits of particles.