The investigation of the feature of dispersion induced turbulence and its effects on dust explosions in closed vessels

Abstract

The integral scales and rms turbulent velocities of dispersion induced turbulence measured in three explosion vessels of different sizes (6, 26, and 950 liter) and shapes, with different dispersion systems, are within the ranges of 0.4–1.6 cm and 0.5–3.3 m/s. Experimental results demonstrate that a steady turbulent flow acts on the combustion process in the 950 liter sphere, while a transient turbulent flow occurs in the 6 liter bomb and 26 liter closed tube. The systems studied are typical for laboratory pneumatic dispersion systems in explosion test vessels. All of these systems produce turbulence with “high intensity and relatively small scale” which has no analogue with the expected natural conditions of accidental explosions in industry. The numerical values of the turbulent burning velocity are determined as a linear function of the rms turbulent velocity produced by the pneumatic dispersion systems in cornstarch-air mixtures. These values are compared with the data, which were determined under the same experimental conditions using the same procedure for experiments, for methaneair mixtures. Because the order of magnitude of turbulent burning velocities measured in cornstarch flames is the same as in lean methane flames, it is inferred that the processes controlling flame propagation in these flames-should be similar. The integral scale of turbulence produced by these dispersion systems is of the same order of magnitude as the laminar flame thickness, and the rms turbulent velocity is much larger than the laminar burning velocity in both the cornstarch-air and lean methane-air mixtures. As a result of these relations the ratio of the mixing rate to the chemical reaction rate is higher than eight, which indicates that the flames propagate under conditions close to those in which quenching by turbulence takes place.