An Improved Solution for Shielding of Thermal Radiation of Fires Using Mist Curtains of Pure Water or Sea Water

Abstract

An improved theoretical model for the shielding of radiation from large-scale fires by the mists of pure water or sea water is presented. This is a continuation of a recent study by accounting for both the partial re-absorption of radiation in the absorption bands of gases and the variation of the incident radiative flux along the flame. As before, the solution to a combined problem of heat transfer consists of the spectral radiative transfer in a mist curtain, the kinetics of droplet evaporation, and convective heat transfer along the curtain. The previously suggested spectral models for optical properties of water droplets and salt particles formed by evaporation of sea water droplets are used in the calculations. Unlike in our previous study, the radiative heat losses to the nozzle head and the floor under the curtain and the decrease in the downward velocity near the floor are accounted for the first time using the 2-D radiative transfer calculations. It is shown that heat losses towards the floor and nozzle head are insignificant even for thick water curtains. Some recommendations on correct choice of parameters of two-layered mist curtains with relatively low total flow rate of supplied water are given. In particular, it is confirmed that the use of smaller droplets of water in the second layer of mist curtains reduces the required total flow rate of supplied water. It is also shown that the protection offered by sea-water curtain is almost the same as that of pure water. Moreover, the use of sea water is potentially preferable for better protection from the fire radiation in the lower part of the curtain. The latter statement is correct in the case of high protective mist curtains, when the droplets of pure water evaporate completely before reaching the floor, whereas the hollow particles of sea salt are there in the lower part of the sea-water mist curtain. The study confirms that sea-water curtains can be used in coastal areas, offshore platforms or maritime transportation ships for shielding fire thermal radiation.