Burning process over a thermally thick material with varying unheated lengths under forced airflow

Abstract

This paper studied the effects of an unheated segment on solid burning under laminar forced flow, where both experimental and theoretical analysis of the burning behavior of a non-charring solid fuel was investigated. Polymethyl methacrylate (PMMA) samples measuring 10 × 10 × 1.5 cm3 were investigated under a forced airflow where the effect of unheated starting lengths (5, 10, 20 cm) on the burning behavior was studied by introducing a dimensionless Nusselt number. Experimental results demonstrated that the burning PMMA was divided into three sections: leading, mid, and trailing sections. The theoretical and experimental Nusselt numbers showed a better agreement in the leading section. At a shorter unheated length, the steady burning rate was approached faster because of increased heat transfer. Additionally, comparing the effects of the forced airflow and unheated segment on solid burning, it was found that the effect of wind velocity on the pyrolysis rate of PMMA samples largely depended on the unheated length. For shorter unheated lengths, the increased wind velocity had a more pronounced effect on the increased burning rate in the trailing section. However, for longer unheated lengths, the effect of wind velocity on the burning rate was similar in the streamwise direction.