Turbulent flame propagation in corn dust clouds formed in confined and open spaces

Abstract

Flame propagation stages in a corn dust cloud in a large room size confinement investigated. The clouds ignited by a weak heat source. The mass of the dust identified to be influenced the flame acceleration. Dust in the clouds burnt rapidly through several fluid dynamic mechanisms. Four types of instabilities contributed to fast flame development. Landau-Darrieus and Kelvin-Helmholtz instabilities increased the flame speed in the initial stages of the fireball. In the intermediate and final stages, corrugated and the wrinkled flame structure originated through Rayleigh-Taylor instabilities. In addition to flow aspects and instabilities, the shock waves also enhanced the flame speed. The shock overpressure measured with a dynamic pressure sensor. These shock waves induced Richtmyer-Meshkov instability in the fireball and developed turbulent flames. Density gradients across the fireball (due to higher temperature gradients) caused perturbations. Further, this gradient increased by the shock waves. The crosswind speed through the confinement windows was slower, therefore it has not enhanced the flame speed. Corn dust dispersed quickly to a wider area by the shock waves, established large dust clouds, and lead to explosions. The maximum surface temperature of the fireball predicted as 1384 K. The preheat zone around the fireball identified by an image processing tool. The turbulence parameters at the fireball obtained from qualitative and quantitative methods and analyzed. The clouds of a small quantity of corn dust lead to the formation of larger fireballs due to higher kinematic viscosity than the energy dissipation rate. Keywords Dust cloud explosion • Hydrodynamic instability in dust cloud explosions • Turbulent flame • Fire accidents and Fire safety List of symbols LDI (DLI) Landau-Darrieus instability also referred to as Darrieus-Landau instability KHI Kelvin-Helmholtz instability RTI Rayleigh-Taylor instability RMI Richtmyer-Meshkov instability DAQ Data acquisition system FPS Frames per second R e Reynolds number D a Damköhler number K a Karlovitz number p D Dynamic pressure Fluid density u ′ Turbulent intensity, velocity component L T Integral turbulent length scale L

Explosion Severity of Rice Dust in a Spherical System

“…technical report). Higher volatility translates to a more combustible dust [21]. Thus, it can be concluded that brown rice, white rice, black rice, Bario rice, and glutinous rice are combustible and can accelerate explosion propagation.…”

“…6 shows a congruent trend for dried rice, in which dried brown rice with the lowest moisture content (6.0 wt %) gave the highest explosion pressure at 18.9 bar, while Bario dried rice with the highest moisture content (9.0 wt %) recorded the lowest explosion pressure (11.1 bar), demonstrating the moisture content effect on the maximum overpressure development. Moisture could induce the agglomeration of dust particles, increase the dust effective particle size, and weaken the dust cloud dispersion [24][25][26][27]. The result is a significant reduction in blast severity and dust combustibility for white rice, black rice, and Bario rice.…”