Date of Award
Master of Science (MS)
Dust explosibility data are a critical input to the design of equipment and strategies for reducing the risk of a combustible dust deflagration or explosion. These data, which include minimum explosible concentrations, deflagration indices, and explosion overpressures, are obtained using formally accepted, standard techniques, and are known to be sensitive to the particle size characteristics of the dust being evaluated. Published literature demonstrates that the standard techniques can alter the particle size distribution during dispersion, making interpretation of the explosibility data challenging because the particle characteristics are altered from their original, raw state. Digital in-line holography (DIH) presents a novel method for measuring airborne dust particle size distributions and imaging three-dimensional particle flows during dispersion to characterize the changes to the particle size characteristics and to investigate the underlying mechanisms. In this work, a DIH imaging system was designed to work in conjunction with a dust dispersion system to capture particle size distributions of dust clouds exiting a nozzle. The image capture system utilizes a 21 mW helium-neon laser to create a hologram of pressurized dust as it passes through a nozzle and into a 2.5 L chamber. A study conducted to quantify the resolution of holographic particle location, established an average in-plane resolution of 10.51 µm with a lens and 20.31 µm without a lens. The residual standard error for axial measurements taken of a resolution target, sugar particles, and lycopodium particles ranged from 80.41 – 146.19 µm without a camera lens and 66.63-98.58 µm with magnification from a camera lens. Holographic analysis of dispersion videos of non-brittle (lycopodium) and brittle (ascorbic acid) dust, using HoloSand analysis tools, resulted in less than 15\% reduction in particle size for lycopodium and more than 50\% reduction for ascorbic acid. The particle size distribution of the ascorbic acid was also shown to decrease with an increase in dispersion pressure. The scale of the particle distribution change for both materials was consistent with results from previous studies using the 20-L Siwek vessel, validating the dispersion and DIH imaging method.