Effect of Thickness on Downward Flame Spread over Paper

摘要

An experimental study has been conducted to explore the effect of thickness on downward flame spread over thin solid-fuel sheets in an upward air stream. Flame spread rates over paper of four different thicknesses at various air-stream velocities were measured, and the gas velocity and temperature profiles in the vicinity of spreading flames were examined using particle tracer techniques and fine-wire thermocouples. It was confirmed that the spread rate of a stably spreading flame decreased with the increase of the thickness. The gas velocity profile in the vicinity of the leading edge of the preheat zone and the gas temperature profile in the preheat zone were almost independent of the paper thickness. In the case of stable flame spread, the mass burning rate decreased with the increase of the air-stream velocity and increased with the increase in thickness. The increase of the mass burning rate with the paper thickness was confirmed to be partly due to the heat transfer to the unburned material through solid phase, and mainly due to the existence of the solid-phase temperature difference in the direction normal to the paper surface.