Multipoint radiation induced ignition of dust explosions: turbulent clustering of particles and increased transparency

Abstract

It is known that unconfined dust explosions consist of a relatively weak primary (turbulent) deflagrations followed by a devastating secondary explosion. The secondary explosion may propagate with a speed of up to 1000 m/s producing overpressures of over 8-10 atm. Since detonation is the only established theory that allows a rapid burning producing a high pressure that can be sustained in open areas, the generally accepted view was that the mechanism explaining the high rate of combustion in dust explosions is deflagration to detonation transition. In the present work we propose a theoretical substantiation of the alternative propagation mechanism explaining origin of the secondary explosion producing the high speeds of combustion and high overpressures in unconfined dust explosions. We show that clustering of dust particles in a turbulent flow gives rise to a significant increase of the thermal radiation absorption length ahead of the advancing flame front. This effect ensures that clusters of dust particles are exposed to and heated by the radiation from hot combustion products of large gaseous explosions sufficiently long time to become multi-point ignition kernels in a large volume ahead of the advancing flame front. The ignition times of fuel-air mixture by the radiatively heated clusters of particles is considerably reduced compared to the ignition time by the isolated particle. The radiation-induced multi-point ignitions of a large volume of fuel-air ahead of the primary flame efficiently increase the total flame area, giving rise to the secondary explosion, which results in high rates of combustion and overpressures required to account for the observed level of overpressures and damages in unconfined dust explosions, such as e.g. the 2005 Buncefield explosion and several vapor cloud explosions of severity similar to that of the Buncefield incident.

Theoretical Model Development for Energy Motion of Dusty Turbulent Flow of Fibre Suspensions in a Rotational Frame

“…e energy motion equation of the dusty turbulent flow of fibre suspension (19) was derived in a rotational frame. is new equation was developed in the 2nd order tensors of pressure-velocity and velocity-velocity correlation at any two points C and D of the fluid flow field.…”

“…A precise and exact calculation of the collision rate includes an accurate understanding of the collision rate impacts caused by turbulence and preferential or clustering particle concentrations. Several studies [13][14][15][16][17][18][19][20][21] have been carried out on the motion of the dusty turbulent flow. e characteristics of the dust particles [22][23][24][25] mainly rely on the particle size of the turbulence scale.…”

Dataset for the Heat-Up and Heat Transfer towards Single Particles and Synthetic Particle Clusters from Particle-Resolved CFD Simulations

“…Heat transfer, mass transfer, and particle drag are calculated based on the representative particle diameter for each parcel, neglecting any agglomeration or grouping effects. It is essential to consider flow shielding, radiation shading, and other inter-particle effects to predict the particle heat up and the thermo-chemical conversion within particle clouds or dense particle jets correctly [7][8][9][10][11][12][13][14].…”

Heat Transfer Models for Dense Pulverized Particle Jets

“…This parcel approach implies simplifications to the conservation equations of parcels since poly-disperse particle mixtures are cut down to single representative particles [10,11]. The convective and radiative heat flux towards such computational parcels might be overpredicted if parcels are interpreted as physical particle clusters in turbulent flow because the modeling approach disregards flow shielding and radiation shading of the particles in the central cluster regions [12][13][14]. These effects might be captured by suitable representative particles or appropriate heat transfer correlations.…”

“…Inter-particle effects in parcels or between parcels are also disregarded for simplicity in common Euler-Lagrange models. Haugen [12], Liberman et al [13], Forgber and Radl [15] showed that these effects are essential to correctly predict the heat transfer within clouds of pulverized particles. Furthermore, thermochemical conversion is also affected by clustering effects.…”