Impact of particle diameter and thermal radiation on the explosion of dust layers

Numerical simulations were performed to study the impact of thermal radiation and particle diameter on layered coal-dust explosions. The geometrical setup considered the interaction of a primary explosion with a thin layer of coal dust inside of a closed channel. The simulations solved the compressible reacting Navier–Stokes equations coupled to an Eulerian granular multiphase model. Thermal radiation was included by solving the radiation transfer equation using the filtered spherical harmonics approximation. The results show that the impact of radiation on the dust explosion is situation specific. Radiation can promote, inhibit, or have little impact on the explosion depending on the particle diameter. Radiation has a slight inhibiting effect on dust layers comprised of 30 and 100 $\mu$m-diameter coal particles. Radiation quenched the explosion when particles were 5 $\mu$m in diameter. Radiation promoted stable burning for larger 150 $\mu$m-diameter coal particles, while simulations excluding radiation for 150 $\mu$m-diameter coal particles produced a failed explosion. The influence of particle diameter on the dispersibility characteristics of dust layers has a significant impact on the explosion. Small 5 $\mu$m-diameter coal particles are dispersed poorly by the leading shock and are too highly concentrated to burn. Large 150 $\mu$m-diameter particles disperse higher into the channel and show improved mixing, but have large thermal time scales that inhibit vigorous reaction. Cases with 30 and 100 $\mu$m-diameter particles show a good compromise between dispersibility, mixing, and thermal time scales which produce stable combustion with or without the inclusion of thermal radiation in the model.