Abstract
The extinction limits of a small propan diffusion flame by usual dry powders were studied experimentally. The powder was added to the oxygen-nitrogen mixture flowing at the outside of burner flame through an injection feeder, and the extinguishing limit concentration of the powder was measured by a light attenuation method under the change of experimental conditions such as mean particle size, mean specific surface area, ambient oxygen concentration and powder material. Dry powders used are three kinds of commercial grade sodium hydrogencarbonate, potassium hydrogencarbonate and ammonium dihydrogenphosphate.
The results obtained are summarized as follows:
(1) The extinguishing limit concentration of screened uniform powder lowers with the decrease of the oxygen concentration in ambient gas flow and the particle size.
(2) The extinguishing limit concentration is in a linear relation with the reciprocal of specific surface area of the powder, and the plotted line approximately passes the origin.
(3) The extinction effect for three kinds of dry powder used here is decreased in the order of KHCO3 > NaHCO3 > NH4H2PO4. The cause that the NH4H2PO4 powder for practical use is in appearance more effective than NaHCO3 will be mainly originated in the small mean particle diameter.
(4) The flame extinction effect of two component mixture with NH4H2PO4 decreases in comparison with the ones of individual powder and other combination without NH4H2PO4.
The authors also suggest in this paper that the slope of the line mentioned in (2) may be used as an evaluation index of the fire extinction ability of dry powders.
