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Characterization of the diffusion flame established along a solid fuel in natural convection by the mass transfer number

Yannick PIZZO, doctorate of University of Provence (Ecole polytechnique universitaire de Marseille, Institut universitaire des systèmes thermiques industriels (Iusti)), 72p., defended on the 28th november 2007

Document type > *Mémoire/HDR/Thesis

Keywords > Zircaloy-4, grassland

Research Unit > IRSN/DPAM/SEMIC/LIMSI

Authors > PIZZO Yannick

Publication Date > 28/11/2007

Summary

The rate of pyrolysis of a fire-exposed solid fuel is a key parameter to evaluate the intensity of fire and its effects on surroundings. The present study is experimental, theoretical and numerical.
It focuses on the determination of the steady-state pyrolysis rate of a vertical slab of PMMA. An original experimental set-up is thus developed along with a specific procedure in order to locate the regressing surface of the solid material. A theoretical approach which is based on the reactive laminar boundary layer theory (LBL) assumptions and a numerical two-dimensional CFD model are used. Experimental results show that a three-dimensional behavior appears for small slab widths. In the laminar part of the flow, near to the leading edge, experimental and numerical results reveal a decreasing power-law of the pyrolysis rate, in agreement with the LBL theory. Radiative and convective effects that are not taken into account by the theory are responsible for discrepancies on scaling laws. The assumptions of the LBL theory are discussed. It is found that for free flows the pyrolysis rate is inversely proportional to the normal gradient of the gas velocity at the fuel surface.
A transient pyrolysis model based on the mass transfer number is proposed, avoiding the calculation of the thermal and flow fields of the gas phase.

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Laurent Audouin, the thesis supervisor

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Thesis report


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