The Ignition of low-exothermicity solids by local heating


Shah, A., Brindley, J., McIntosh, A., Griffiths, J. and Pourkashanian, M. (2004) The Ignition of low-exothermicity solids by local heating. Process Safety and Environmental Protection; Official Journal of the European Federation of Chemical Engineering: Part B, 82, (B2 Special Issu), 156-169. (doi: 10.1205/095758204322972799).

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Description/Abstract

In this paper we bring together a number of recent studies associated with the burning of low-exothermicity porous materials that are inadvertently, or otherwise, exposed to a maintained heat source (hotspot). Additionally, we provide some new results in the form of dimensionless ignition criteria, which allow us to generalize previous results to a broader class of materials and to larger sample sizes. It is shown that systems of the type described can be represented by a hierarchy of mathematical models, depending on whether oxygen is in limited supply, is not required (as in the case of thermal decomposition), and/or a significant volume of gaseous products is present. We summarize the behaviour of systems in which gas motion through the solid pores has a negligible effect, including cases where the burning is dependent on a limited supply of oxygen. The effects of geometry and initial-boundary conditions are discussed. Finally, for reactions involving gaseous products, we present numerical solutions to a system of equations that incorporates the gas motion through the solid pores by employing Darcy's law. In comparison with the previous cases, it is demonstrated that ignition of low-exothermicity materials is more difficult to achieve (a larger hotspot heat-flux is required), essentially because of transportation of heat by advection towards the unburnt solid, and, consequently, increased reactant depletion. Furthermore, ignition will always take place away from the hot-spot surface; this is in complete contrast to highly exothermic materials, in which reactant depletion is negligible during the early stages of ignition, and in which ignition occurs at the hotspot boundary.


Item Type: Article
ISSNs: 0957-5820 (print)
Subjects: Q Science > Q Science (General)
Divisions: University Structure - Pre August 2011 > School of Engineering Sciences > Thermofluids and Superconductivity
ePrint ID: 44777
Date Deposited: 16 Mar 2007
Last Modified: 27 Mar 2014 18:29
Contact Email Address: A.Shah@soton.ac.uk
URI: http://eprints.soton.ac.uk/id/eprint/44777

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