Thermal explosion in oscillating ambient conditions.

Vasily Novozhilov

doi:10.1038/srep29730

Abstract

Thermal explosion problem for a medium with oscillating ambient temperature at its boundaries is considered. This is a new problem in thermal explosion theory, not previously considered in a distributed system formulation, but important for combustion and fire science. It describes autoignition of wide range of fires (such as but not limited to piles of biosolids and other organic matter; storages of munitions, explosives, propellants) subjected to temperature variations, such as seasonal or day/night variation. The problem is considered in formulation adopted in classical studies of thermal explosion. Critical conditions are determined by frequency and amplitude of ambient temperature oscillations, as well as by a number of other parameters. Effects of all the parameters on critical conditions are quantified. Results are presented for the case of planar symmetry. Development of thermal explosion in time is also considered, and a new type of unsteady thermal explosion development is discovered where thermal runaway occurs after several periods of temperature oscillations within the medium.

Highlights

Thermal explosion problem for a medium with oscillating ambient temperature at its boundaries is considered
In contrast to the basic Semenov thermal explosion problem[9] where critical conditions are determined by the balance between self-acceleration of the chemical reaction and the rate of heat dissipation, in the case of dynamic regimes with monotonically increasing ambient temperature existence of critical conditions is mostly due to reactant consumption
The present paper considers the problem of thermal explosion development in oscillating ambient conditions

Summary

Vasily Novozhilov

Thermal explosion problem for a medium with oscillating ambient temperature at its boundaries is considered. In contrast to the basic Semenov thermal explosion problem[9] where critical conditions are determined by the balance between self-acceleration of the chemical reaction and the rate of heat dissipation, in the case of dynamic regimes with monotonically increasing ambient temperature existence of critical conditions is mostly due to reactant consumption (i.e. kinetic factors) It is clear from this qualitative consideration that if one considers a certain value w∼ > w∼⁎ and take a temperature grow profile that deviates (becomes slower) from the linearT (t) = w∼tat sufficiently large values of time, explosion will occur for such a type of the profile. This builds a framework for interpreting behaviours of more complicated systems, and allows the generalization of the results to be made

Mathematical Model

At the symmetry plane in the middle of the slab

Results and Discussion

Conclusions

Additional Information