Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Gerhard, Jason I.

2nd Supervisor

Torero, Jose L.

Co-Supervisor

Abstract

Smouldering combustion is defined as a flameless oxidation reaction occurring on the surface of the condensed phase (i.e., solid or liquid). Traditional research on smouldering was related to economic damages, fire risk, and death, due to the release of toxic gases and slow propagation rates. Recently, smouldering has been applied as an intentional, engineering technology (e.g., waste and contaminant destruction). Smouldering involves the transport of heat, mass, and momentum in the solid and fluid phases along with different chemical reactions. Therefore, numerical models are essential for the fundamental understanding of the process. Smouldering models either neglected heat transfer between phases (i.e., assumed local thermal equilibrium) or employed heat transfer correlations (i.e., under local thermal non-equilibrium conditions) not appropriate for smouldering. Thus, the first step of this thesis was to develop and validate a new heat transfer correlation for air flowing through hot sand at conditions appropriated to smouldering. The new correlation was reliable and predicted well heat transfer between phases. The second step was to apply the new correlation along with appropriate chemistry into a one-dimensional model. The model was calibrated to a smouldering experiment of an organic liquid fuel embedded in sand and then confidence in the model was gained by independent simulations of additional experiments. Local thermal non-equilibrium demonstrated to be essential to correctly simulate smouldering of organic liquid fuels embedded in sand. Moreover, a two-step kinetic mechanism showed to be sufficient to simulate the smouldering chemistry. The third step was to use the one-dimensional model to understand the conditions that lead to self-sustaining smouldering and smouldering extinction. A global energy balance was developed, revealing that self-sustaining and extinction conditions occurred when the net energy balance was positive and negative, respectively. The last step was to use the one-dimensional model to conduct a sensitivity analysis of the key practical model parameters. Moreover, a local energy balance was developed and compared with the global energy balance; both were used to explain the physics of the process. It was found that the local energy balance described the moment of extinction, whereas the global energy balance predicted extinction in advance. Overall, this thesis presented new insights into the interplay between heat transfer and chemical reactions along with the understanding of the conditions that lead to self-sustaining smouldering and smouldering extinction.

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