(421i) Effectiveness of Dust Dispersion: Visualization Study in Siwek 20-L Chamber

Dust explosion severities can be strongly affected by the ignition delay, which is closely associated with dust dispersion behavior. To characterize the dispersion process of dust cloud, systematic experiments were conducted by using a transparent Siwek 20-L chamber. Dispersion behavior of typical carbonaceous dust was recorded by a high-speed camera, and qualitative analysis was also carried out based on the recorded frame pictures with the image processing technique. Experiments have evidenced three consecutive stages of dust dispersion process: a fast dust injection phase, stabilization of dust cloud and sedimentation phase. Both the motion of dust particles and the non-uniformity of dust cloud in space and time can be clearly distinguished. The stabilization of dust cloud can be clearly identified from the transmission-time (T - t) trace, and the variation of stabilization time range with dust concentration suggests that a suitable ignition delay is necessary for relatively accurate tests of dust explosion characteristics in Siwek 20-L chamber. Moreover, with the recommendation of Bouguer-law, transmission data is inversely proportional to dust concentration; however, it is found that the decrease of transmission is gradually leveling off with dust concentration, and this significant deviation from ideal case indicates the much lower actual dust concentration and the less effectiveness of dust dispersion, especially in high dust concentration. In addition, the stabilization of transmission attained after dust concentration exceeds to 1000 g/m³ also suggests that the maximum dispersion concentration is existed for a certain test condition.