固体延焼の基礎的研究 その5
鉛直円柱の有炎燃え下がりの場合における炎からのふく射の効果

抄録

A piece of filter paper was rolled several turns to form a circular rod of 3.8 mm radius. When this rod was kept vertically and was kindled at its top, a flame proceeded downward.
Heat is transferred to an unburnt part by both the conduction through paper rod and the radiation from the flame. When the heat quantity given to the part comes up to a certain value, combustion reaction begins in this part resulting in the flame propagation to this layer. The study reported in this paper is concerned with the ratio of heat quantities transferred in both ways.
In order to observe heat radiation from the flame, we used a small square (2 mm × 2 mm) aluminum foil (thickness = 0.075 mm), on a surface of which the junction of a thermocouple of copper-constantan (dia = 0.12 mm) was stuck to form a radiometer of small size. Both surfaces of the foil were blacked out to make the radiometer more sensitive to the incident radiation. Its sensitivity was calibrated by a conventional thermopile-type standard radiometer.
The intensity of radiation on the radiometer, placed as close to the rod-surface as possible, was observed when the flame front attained to a point adjacent to the radiometer. From these reults, the incident radiation per unit time on the side of the disk, supposed in the rod just under the flame front, was calculated. On the other hand, heat gains by conduction per unit time of this disk was calculated from the temperature distribution in the rod and the conductivity of the filter paper.
Comparing both values, it has been found that the ratio of radiation intensity to the conductive heat gains is as small as 6.2/180. In setting up a theory of flame propagation along a vertical rod, therefore, one can ignore the effect of heat radiation, as a first approximation, compared with the heat conducted through the rod.