Abstract
This report includes the discussion about the relationship between the range of explosion for the fuel-air-dry powder system and the extinguishing effectiveness of dry powder against fires of various liquid fuels.
The range of explosion was measured by the apparatus shown in Figure 2. The extinguishment was effected using the apparatus shown in Figure 3. The former′s results are summarized in Figure 4, and the latter′s in Table 2.
Through these results, it is concluded that the mixture of fuel-air does not explode, when the sufficient dry powder of concentration P (P is a peak concentration, g/l) disperses in the mixture. Similarly, the flame goes out, when the dry powder of concentration P/(1-c) (c is a fuel concentration in the fuel-air mixture at the peak concentration) disperses in the surrounding air. Further, the minimum necessary discharge rate E (g/min) is expressed as :
E=(P/ｃ) · V=(P/ｃ) · (22.4/M) · W=(P/c) · (22.4/ M) S · V · ρ (1)
where, V is the gaseous fuel volume evaporated or discharged in unit time (l/min), M the molecular weight of fuel, W the fuel weight evaporated in unit time (g/min), S the surface area of tub (cm2), the burning velocity of fuel (cm/min), and ρ the density of fuel (g/cm3), respectively
In the extreme right column of Table 2 is given the ratio of experimental value of discharge rate to the value calculated by the equation presented in footnotes. Three cases ware discussed in order to explain the ratio being greater than unity.
