Modeling and Measurement of Dust Dispersion Patterns in Confined Spaces
Abstract
In the grain handling and processing industry, dust emission and accumulation are major concerns for the safety of workers and for explosion risks. Dust emission and accumulation locations highly depend on the facility design and equipment used for handling and processing. To prevent an explosive atmosphere, monitoring the amount of dust accumulated or dispersed is extremely important. However, methods of measuring the dust concentration require the installation of equipment. The Occupational Safety and Health Administration (OSHA) regulations and National Fire Protection Association (NFPA) standards restrict the thickness of dust layers on floors for fine powder materials such as starch. The objective of this dissertation was to better understand the rate of dust layer accumulation, dust suspension patterns, and the optical properties of suspended dust. For this purpose, The Discrete Phase Model (DPM) was combined with a Computational Fluid Dynamics Model (CFD) and the hybrid model was used to model dust dispersion. Dust dispersion patterns under pressure, such as primary explosions or leakage from equipment, were simulated using the unsteady CFD-DPM approach. The particlewall interaction based on energy conservation was also introduced in this model. Both one-time and continuous dust dispersion in an enclosed chamber were simulated to mimic secondary explosions and the dust emission from processing equipment. In addition, the light extinction property of suspended dust was studied as a method of measuring suspended dust concentration. For a one-time dust dispersion incident, the predicted dust concentration agreed with the simulation result for the trial conducted at a dust injection velocity of 2 m/s with injection rates of 0.05 and 0.10 kg/m³ and at a dust injection velocity of 10 m/s with an injection rate of 0.05 kg/m³. The dust concentration in the entire chamber increased with dust injection velocity and the mass of injected dust. As dust injection velocity increased, dust spread out and formed a larger explosive dust cloud. However, the dust concentration inside the chamber was non-uniform. Considering the minimum explosive concentration, the largest explosive cloud was created at a dust injection velocity of 10 m/s with an injection rate of 0.10 kg/m³. Explosive concentrations of dust were found somewhere in the chamber for all dispersion rates. At an injection velocity of 10 m/s with an injection rate of 0.10 kg/m³, the predicted dust concentration was 10% more than the measured dust concentration. Thus, this model is suitable for dilute dust particle dispersion flows, where the volume fraction of particles is less and only a single particle layer settles. Continuous dispersion was simulated to determine the suspended dust concentration and particle deposition patterns. Dust was dispersed for 30 s at dispersion rates of 2, 4 and 6 g/min at a dust injection velocity of 2 m/s. The dust concentration increased at a constant rate after a few seconds of dispersion, regardless of the dust dispersion rate. Most dust particles were deposited near the dust dispersion nozzle. Large particles were more affected by gravitational force and inertia compared with small particles, which traveled with airflow and settled behind the nozzle. The dust accumulated close to the dispersion nozzle faster than behind the nozzle location.
Degree
Ph.D.
Advisors
Ambrose, Purdue University.
Subject Area
Energy|Occupational safety|Fluid mechanics|Health care management|Management|Mechanics
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