Numerical and Experimental Investigation on Particle Disposition and Distribution in Ventilation Duct Bends

Understanding the particle flow is important for solving these indoor environmental quality (IEQ) problems and controlling the particle concentration, distribution and deposition. Therefore, this dissertation aims to investigate these particle phenomena in bends of mechanical ventilation (MV) systems by means of numerical models and experimental measurements.;Numerical predictions were conducted to investigate the particle flow movement and deposition in a 90° bend after a straight duct, utilizing the Lagrangian particle-tracking model incorporated with a particle-wall collision model. The developed models were validated by the current measurement results and previous experimental data. The simulation results showed that, compared with the traditional 'Trap' model, the particle-wall collision model postponed the emergence and slowed the increase of the 'particle free zone' as the particle diameter increases. Particle deposition velocity in the duct bend was also generally predicted by the proposed estimation equation under the simulated conditions. Duct bend wall with the material of the largest capture velocity is easy to accumulate contaminant particles.;Scanning Electron Microscope (SEM) was adopted to explore actual ventilation ducts with deposited dusts. Systematic experiments were also designed to validate the numerical studies, and to investigate the real aerosol deposition in rectangular section bends. The measured results at Reynolds number Re=17900 and 35600 showed a general agreement with previous published data, models and the numerical prediction in this thesis. Dust deposition velocity was roughly higher than previous studies probably due to the consideration of particle rebounce from wall. Empirical models were proposed, and they were valid for dimensionless relaxation time from 0.34 to 27.6 under present experimental conditions. Compared to penetration, deposition velocity is more sensitive to initial concentrations and wall materials. Furthermore, apexes and concaves of the outlet distribution are inferred to be formed by the rebounding particles from the outer wall. Quantitatively, present experiments give specific areas for particle of specific diameter range for "particle free zone" under current measuring conditions.;The findings and developed models in this thesis could benefit the understanding of particle flow in bends, guide the design of ventilation duct, and help control the particle pollution through the ventilation system.