Turbulence effects on dust explosions in the 20-liter spherical vessel

Abstract

The method of collecting a large amount of data and taking ensemble average over all measurement periods using computer is employed to determine the turbulence parameters during the transient dispersion process in the 20 liter spherical vessel. The system studied is typical for laboratory pneumatic dispersion systems in explosion test vessels. Measurements show that a decaying turbulence feature is generated by the dispersion system and characterized by a decay period of 150–300 ms with the integral scale of about 1 cm and initial intensity of about 3 m/s, which has no analogue with the expected natural conditions of accidental explosions in industry. Two kinds of dust-air mixtures (aluminum and cornstarch) and methane-air mixtures, three different sizes of aluminum dust particle (5, 15, 30 μm) and one average size of corntarch dust (15 μm) are tested in this sphere. The maximum burning velocity is used instead of Kst factor to characterize the highest combustion rate occurred during the explosion process in the closed vessel for both dust and gas-air mixtures. The present experimental results demonstrate that the maximum burning velocities determined as a linear function of the initial rms turbulence velocity produced by the pneumatic dispersion system in the aluminum- and cornstarch-air mixtures. The experimental results also demonstrate that the reduction of dust particle size will increase significantly the turbulent buring velocity in dust-air mixtures, but the kind of dust seems to have no significant influence on explosion data, if their particle sizes are the same. These suggest that the dispersion induced turbulence may play more important role in formation of dust-air mixtures than in direct effect dust combustion process, and that the influence of the above turbulence on the combustion characteristics mainly enters through the mechanisms of creating uniform suspension of dust clouds.