Finely-dispersed water fire radiation screening

Abstract

The theoretical and experimental study results of finely-dispersed water droplet flow features screening fire heat radiation are shown. Water curtains offer cooling and fire with its danger factor spread prevention (OFP) through window, door and technological openings, outside protected equipment, area or rooms, as well as safe people escape provision from rooms on fire. In designing water curtain generation devices, as a rule, there aren’t taken into account curtain parameters defining their protection features, such as screening factor, droplet diameter and their concentration. Fire protection curtain efficiency depends to a lesser extent on fire temperature but to a greater extent it depends on water droplet diameter and water flow rate. A relatively efficient and water flow-rate-effective curtain can be designed with sprayer generated droplets of less than 200 mm diameter. With droplet size of more than 500 mm the infra-red fire radiation is screened by less than 25 %. Single-fold dispersion for finely-dispersed water with r = 20 mm droplet radius and n = 10¹⁰ m^-3 droplet calculated concentration is possible in a few centimetre length. In considering screening curtain features the average Zauter diameter d₃₂ plays an essential role, particularly it refers to a multiple dispersion that considerably (by 4…5 fold) decreases radiation falling onto the screen. Fine droplets usage d₃₂ < 100 mm in diameter is connected with certain features of that flow. This also relates to an output sprayer nozzle, the diameter of which greatly effects the size of generated droplets: the less the nozzle diameter, the less average Zauter diameter of the droplets in the spray cone. A great droplet diameter dependence follows from output sprayer nozzle liquid velocity value that turns into a droplet flow while interacting with the ambient air, thereby the greater an output liquid velocity, the smaller the droplets. The experimental data analysis shows that infra-red radiation shade coefficient increase is connected with volumetric droplet concentration (curtain flow rate), and average median diameter decrease (droplet flow dispersion).