The effect of particle size polydispersity on the explosibility characteristics of aluminum dust

• Aluminum samples having similar D50 and varying size polydispersity were tested.
• Pmax and KSt values of aluminum samples increase with size polydispersity.
• D50 and D4,3 are inadequately related to KSt values of samples having broad PSD.
• D3,2 exhibits the best correlation between particle size and explosion severity.

This paper reports experimental results elucidating the effect of particle size polydispersity (σD) on the explosion severity of aluminum dust. Five mixtures with a median diameter (D50) of 15 μm and σD values of 0.95, 1.17, 1.48, 1.87, and 2.51, were systematically prepared by mixing original aluminum samples having narrow size distributions. The explosion severity of each sample was determined in a 36 L dust explosion vessel by measuring the maximum pressure (Pmax), the maximum rate of pressure rise ((dP/dt)max), and the deflagration index (KSt). Interestingly, we found that values of Pmax and KSt revealed an increase in explosion severity as σD increases, where the latter presented a more dramatic effect due to the contribution of fine particles on the combustion kinetics. The effect of dust concentration on the explosion propagation was analyzed comparing the time span to reach (dP/dt)max, (τ), during a dust explosion. τ was obtained from the experimental pressure traces of the original samples and their mixtures. The values of Pmax and KSt were plotted as a function of the median diameter (D50) and the volume- (D4,3) and surface- (D3,2) weighted mean diameter. We observed that D3,2 provided a better description of the average sample size and D50 is inadequately related to the real hazard potential of aluminum dust. Therefore, we suggest that the explosion hazard characterization of these types of materials should be reported in terms of D3,2 and σD.

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