An infrared scattering by evaporating droplets at the initial stage of a pool fire suppression by water sprays

Abstract

h i g h l i g h t sAn initial stage of a pool fire suppression is considered. The motion, heating, and evaporation of water droplets are calculated. Focusing of evaporating water droplets in local regions is obtained. A strong infrared scattering by small water droplets is analyzed. The spectral region of a significant infrared scattering is determined. a r t i c l e i n f o b s t r a c tThe computational analysis of downward motion and evaporation of water droplets used to suppress a typical transient pool fire shows local regions of a high volume fraction of relatively small droplets. These droplets are comparable in size with the infrared wavelength in the range of intense flame radiation. The estimated scattering of the radiation by these droplets is considerable throughout the entire spectrum except for a narrow region in the vicinity of the main absorption peak of water where the anomalous refraction takes place. The calculations of infrared radiation field in the model pool fire indicate the strong effect of scattering which can be observed experimentally to validate the fire computational model.

Two-Step Iterative Method for Radiative Transfer Calculations in Axisymmetric Flames Containing Absorbing and Scattering Particles

“…One should take into account the effects of water sprays on the flow field parameters of the flame in the regular developed regime of fire suppression. However, it is not important in the first stage case of a specific procedure of fire suppression suggested by the authors in recent papers [6,7]. This procedure includes a preliminary probe stage with a very small flow rate of water.…”

“…The examples of such calculations for the case problem can be found in [6,7]. The behavior of water droplets moving along the parallel lines appeared to be quite different, but in all cases the evaporating droplets of different initial sizes are focused on small local regions.…”

“…On the contrary, the large droplets supplied at 1 . 0 0  r m can penetrate to the hot region and totally evaporate during their backward motion at a small distance from this region [7]. It is physically clear that the volume fraction of water droplets increases dramatically in the local regions of their collections and total evaporation.…”

“…Strictly speaking, the assumption of independent motion of single droplets may be incorrect in the vicinity of these regions. Following [6,7], this effect is not considered in the present paper.…”

“…3). The estimates at realistic value of and a non-uniform triangulation with 1600 finite elements was used in FEM calculations [7]. The calculations were performed on laptop with processor Intel Core i5-6300U@2.40GHz and the time of one calculation appeared to be about one second or even less.…”