Effect of the Thickness on Temperature Profiles Near Flames Spreading Downward Over Paper

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  • SUZUKI Masataro
    The University of Tokyo
  • DOBASHI Ritsu
    Department of Chemical System Engineering, Faculty of Engineering, The University of Tokyo
  • HIRANO Toshisuke
    Department of Chemical System Engineering, Faculty of Engineering, The University of Tokyo

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  • 紙に沿った鉛直下方燃え拡がりにおける温度場に及ぼす厚さの影響
  • カミ ニ ソッタ エンチョク カホウ モエ ヒロガリ ニ オケル オンドバ ニ

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Abstract

To explore the flame spread mechanisms over cellulosic solid sheets, the temperature profiles in the vicinity of spreading flames over paper sheets from 1.0 to 6.3-mm thick have been examined by using fine-wire thermocouples. <br>Measured isotherms indicate that the location of the leading flame edge in spreading direction is almost the same for sample sheets from 1.0 to 5.8 mm-thick, and shifts downstream when the sample thickness is 6.3 mm. As reported in the previous paper, the flame cannot spread stably over sample sheets thicker than 7.5 mm. The stand-off distance of the flame at a given station downstream of the leading edge becomes small as the sample thickness increases. However, the maximum value of heat flux to the solid surface from the flame decreases and its location shifts downstream as the thickness increases. As a result, most of heat from the flame to the unburned material transfers through the char layer formed on the sheet. This layer is supposed to be a cause for increasing radiative heat loss since the temperature on its surface becomes higher than the pyrolysis temperature. These results imply heat flux to the preheating region decreases as the paper thickness increases. This decrease of heat flux may cause the stop of flame spread along a thick sample.

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