Construction of a 36 L dust explosion apparatus and turbulence flow field comparison with a standard 20 L dust explosion vessel
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2018 By modifying the dispersion system and the ignition delay time, and hence the flow field and turbulence intensity during the combustion process, various 20 L dust explosion vessels have been calibrated to give results comparable to the 1 m3 vessel as prescribed in the former ISO standard (ISO-6184, 1985). However, the results obtained from experiments conducted in the two vessels do not always agree for the same dust. There can be several reasons for this discrepancy: turbulence decays faster in the 20 L vessel compared with the 1 m3 vessel, the energetic ignition sources used in standardized tests may overdrive the combustion process in the 20 L vessel, and the interaction between the flame front, including radiation emitted from the flame, and the vessel walls is more pronounced for the smaller vessel. This paper details an approach for calibrating a new 36 L dust explosion vessel by utilizing principles for factorial design and analyzing the decay of turbulence following the transient dispersion of the dust clouds by means of computation fluid dynamics (CFD). In the present work, the CFD simulations were used to examine transient injection of air into the 20 L and 36 L vessels, in conjunction with experimental data reported for the 20 liter spherical vessel. Although the vessels considered here had slightly different shapes, sizes, dispersion systems and operating conditions, the simulated turbulence levels were similar at the time of explosion. In addition, the estimates for the laminar burning velocity (SL) obtained using experimental results from the 20 L and 36 L vessels, and assuming the validity of a correlation for the turbulent burning velocity (ST), were also in good agreement. The experimental procedure and multi-variable calibration of the 36 L vessel has been successfully validated by comparing the explosion parameters, such as maximum explosion pressure (Pmax) and size-corrected maximum rate of pressure rise (KSt) to values obtained for the same fuels in a standard 20 L vessel. Furthermore, the experimental results obtained for niacin and cornstarch in the 36 L vessel were in excellent agreement with accepted reference values from literature. It is expected that the same methodology can be used for calibrating other equipment with different configurations where transient turbulence decay has a strong effect on the explosions.
