Analysis of dispersion behavior of aluminum powder in a 20 L chamber with two symmetric nozzles

Abstract

Although aluminum (Al) powder is a potential fuel that has been widely used in many important fields, Al powders are dangerous because of its flammable and explosive characteristics. From this point of view, the investigation of the explosion characteristics of Al powders is of critical importance. The characteristics of a dust explosion are closely related to the dispersion behavior of the powders. The purpose of this research is to analyze the dispersion behavior of Al powder and the uniformity of dust cloud. The dispersion process of Al powders was studied using a high‐speed camera. Image processing technology was applied to obtain the transmission value of the light beam passing through the Al dust cloud at different locations within a vessel. The images obtained by the high‐speed camera indicated that the dispersion process had three stages, that is, a fast injection stage, diffusion stage, and stabilization stage. By examining the transmission‐time histories at 13 different locations in the chamber and at various Al concentrations (from 100 to 800 g/m3), the decay behavior of transmission under different concentrations was obtained, and the decay time fluctuated from 44 to 68 ms. By comparing the deviation of transmission at different locations and for various concentrations in the stabilization stage, the maximum SD obtained was 8.2%, that meant the dust clouds were relatively uniform. Finally, based on the experimental results, the ignition delay time (after which the powder/air mixture is considered homogeneous) corresponding to different dust concentrations should be different to ensure the accuracy of explosion characteristics test.

Investigation on the Explosion Characteristics of an Aluminum Dust–Diethyl Ether–Air Mixture

“…As shown in Figure , the experimental system is composed of a vessel with two symmetrical nozzles, a high-voltage electric ignition system, a control system, a venting pump, a transient pressure measurement system, and a data acquisition system. The details of the two nozzles have been described in our previous work . A pair of tungsten electrodes are installed in the center of the vessel, connected with the high-voltage electric spark generator.…”

“…Once the solenoid valves were opened, the compressed air pushed the mixed samples into the reaction vessel to form flammable clouds. The electric igniter was initiated after a delay time of 65 ms . The explosion occurred after the ignition, and the experimental data were collected by the data acquisition system.…”

CFD simulations of turbulent dust dispersion in the 20 L vessel using OpenFOAM

“…The latter is associated to the nozzle design and spherical geometry of the 20L vessel. Although some authors [52,57] have proposed other nozzles to improve the particle mixing, no conclusive data has been obtained yet.…”

Evaluating the explosion severity of nanopowders: International standards versus reality

“…For non-spherical dusts, the dust dispersion and, especially, the spatial distribution of turbulence, can also be affected by the shape of the dust particles (Di . As a consequence, various authors proposed alternative dispersion nozzles designed to favor the homogeneous distribution of the diphasic flow (Dahoe et al, 2001a;Murillo et al, 2018;Wu et al, 2017;Yao et al, 2020;Zhang and Zhang, 2015). Therefore, explosion severity characteristics obtained are directly dependent on the choice of the nozzle for a specific ignition delay time.…”