Turbulent and accelerating dust flames

Industrial dust explosions kill and severely injure workers as well as destroy property. While the hazards of gaseous explosions are well recognized, the same degree of care has not been exercised with regard to combustible dust. The agricultural industry has been especially plagued by this problem. The research results reported here give data such as the turbulent burning velocity for a suspended dust mixture and the minimum thickness of a dust layer capable of supporting an accelerating flame. To obtain this data two special facilities have been constructed. The first is a premixed turbulent combustion bomb, in which a spatially and temporally uniform dust cloud of known concentration and turbulence intensity is established. The cloud is ignited at the center and the burning velocity is calculated from the measured parameters. The second is a flame acceleration tube in which a uniform dust layer is spread along the bottom. Combustion is initiated at the closed end and the propagation of the flame with the accompanying pressure, velocity, and temperature is monitored as it moves toward the open end. In both facilities runs are made using different kinds, sizes, moisture contents, and mass loadings of dust, and humidity of the air. Much data, heretofore unavailable, is presented. These results should be useful in establishing standards for the prevention of dust explosions, forming strategies to alleviate dust explosions, predicting damage produced by dust explosions, and developing analytical models of premixed and layered dust flames.