Effect of particle size and polydispersity on dust entrainment behind a moving shock wave

To improve the fundamental understanding of dust dispersion with application to explosion safety, a series of experiments was conducted to elucidate the effect of particle size and size polydispersity on dust-layer dispersion behind moving shock waves. Aluminum samples of various average sizes (D3,2 = 1.7-30.3 μm) with varying polydispersity (σD = 0.93, 1.52, 2.62) were the focus of this study. A 3.2-mm layer of Al dust was subjected to shock Mach numbers ranging from 1.23 to 1.52 in a shock tube. The effect of particle density on the dust-lifting process was also studied by comparing aluminum and limestone powders with similar average sizes. The results of the study confirm that particle size and size polydispersity have significant impacts on dust lifting as smaller particles lift higher and faster for a given shock speed. To the best of our knowledge, this work is the first to measure the effect of size polydispersity in a dust layer in a shock tube. New correlations were developed between the shock strength and the dust entrainment height as a function of time. Correlations were also developed to show the relation between dust entrainment height and particle size polydispersity. In summary, the results herein are in agreement with trends found in our previous work, where there is a linear relationship between dust-layer height growth rate and shock Mach number, and with the increase of particle size the dust entrainment height decreases. New data were collected for image analyses, where the longer observation time and higher camera framing rates led to the observation of a clear transition time between the early, linear growth regime of the dust-layer height and a much-slower average growth regime to follow. The dust particle size and polydispersity affected both the growth rate of the dust layer (i.e., the change of dust-layer height with time) and the transition times between the two growth regimes.