THE ROLE OF GAS PERMEATION IN CONVECTIVE BURNING

Convective burning is commonly identified in the literature as the key step in deflagration-to-detonation transition (DDT) of granular explo sives. The prevalent physical picture of convective burning is of rapi d and deep penetration of hot gases which controls the propagation rat e via convective heat transfer. This investigation includes a review o f relevant literature, new transient measurements of permeability at h igh pressures, and analysis of the experimental results. Results prese nted here show that deep penetration (many particle diameters) of gas at high velocities is not physically plausible for the low porosity gr anular beds of interest. The measured permeabilities are consistent wi th measurements made at lower pressures in similar materials, but are significantly lower than predictions based on beds of spherical partic les. The important time and space scales of this experiment are identi fied. The interface region between the reservoir and porous bed is ana lysed. The wave hierarchy of the permeation experiment is studied, and short- and long-time limits are investigated using simplified asympto tic analysis. The low-speed flow approximation is also considered for flow within the bed. It is shown that drag dissipation terms in the en ergy equation cannot be neglected under adiabatic conditions as is com monly done. These results indicate that compaction processes play a la rger role than commonly thought, and motivate the consideration of an asymptotic large drag limit of two-phase, two-velocity models. Publish ed by Elsevier Science Ltd.