SOME CHARACTERISTICS OF TRANSIENT SELF-HEATING INSIDE AN EXOTHERMICALLY REACTIVE POROUS SOLID SLAB

This paper reports the results of numerical simulations and laboratory investigations carried out to explore the characteristics of the tran sient self-heating process. Various initial and boundary conditions we re considered. It was demonstrated that a characteristic temperature, defined as the crossing-point temperature T-P, does not change (to wit hin +/-0.01 degrees C) for the same exothermicity, activation energy, thermal properties, half-thickness and boundary temperature when only the initial uniform temperature is varied. This initial temperature mu st be lower than the critical ignition boundary temperature and the bo undary temperature must not be supercritical to lead to a periphery ig nition. This crossing-point temperature may be used as a physicochemic al property to indicate the propensity of a solid material to self-hea t. The calculations also suggest a linear temperature dependence of th e heat conduction term in the energy balance applied at the symmetry o f a slab for a certain temperature range, from a value smaller than th e crossing-point temperature to a value just before ignition. This con cept of a crossing-point temperature was confirmed by experiments carr ied out on a wood sawdust.