Heat transfer blockage effect of small-scale PMMA flame under exterior heat radiation

In this work, experiments of small-scale vertical and horizontal PMMA flames were performed under exterior heat radiation, in order to investigate the heat transfer blockage effect based on energy balance of steady state. It is found that for both sample orientations, the mass loss rate of PMMA increased linearly with increasing exterior heat radiation, and the flame height depends linearly on mass loss rate to the power 2/3. Calculated and measured mass loss data indicate that the heat transfer blockage fraction is independent of the exterior heat radiation for both sample orientations. For vertical PMMA flame, the radiation blockage fraction increases with vertical height. For horizontal PMMA flame, the radiation blockage fraction is the highest at the sample center. For both horizontal and vertical samples, the mean radiation blockage fraction increases with exterior heat radiation and gradually reaches an equilibrium value. The convective heating to the sample surface is enhanced by hot gas flow for vertical PMMA flame, while it is weakened for horizontal PMMA flame. (C) 2017 Published by Elsevier Masson SAS.