Extinction phenomena in liquids

Abstract

A burning liquid is extinguished when its surface temperature is reduced to the fire point of the liquid. The fire point depends on properties of the liquid and of the atmosphere in which it is burning and a theoretical relationship is given which describes this dependence. This relationship is used to calculate the variation of fire point and critical heat loss at extinction of n-butanol with the oxygen concentration of the ambient atmosphere. The proximity of heat sinks to the surface of a burning liquid may cause extinction and this effect was studied experimentally; the data suggested that liquid layers up to 0.5 mm deep were stationary and heat losses from the surface to the heat sink took place by conduction. Effects of convection were apparent for greater liquid depths. For multi component liquids, mass transfer in the liquid phase also plays a part in determining extinction behaviour. The effects of the degree of internal recirculation on the relationship between the mean composition of a liquid mixture, the surface concentration and the composition of the evolved vapour are discussed. Data illustrating the importance of these effects are given for the ethanol/water system; the minimum concentration of ethanol which would sustain burning in air varied from 7–45%, depending on the degree of recirculation within the liquid. A burner was developed in which the effects of heat and mass transfer in the liquid phase and the oxygen concentration of the surrounding atmosphere on the extinction of a burning liquid could be studied. Some early experiments with this burner are described.