Impact of scattered radiation on thermal radiation shielding by water curtains

[Display omitted] •Conditions are determined of effective thermal radiation shielding by water curtain.•Droplet evaporation parameters in the curtain are established using optical methods.•Thermal radiation shielding depends on droplet size distribution in curtains.•New model estimates the impact of scattered radiation on the thermal transmittance.•The curtain efficiency is decreased twofold or threefold due to scattered radiation. Water curtains are used for shielding thermal radiation from combustion sources. Unlike fire-protection structures, they provide fire containment without blocking the movement of people and they allow firefighters and trucks to approach the combustion source. Water curtains can be produced by fixed-site automatic systems to prevent fire from spreading to the neighboring fire compartment or by nozzles attached to a fire-fighting truck or pipeline. Here we studied the shielding of thermal radiation from a typical compartment fire with a view to developing a prediction model. To record the water curtain characteristics, we used the experimental methods of Particle Image Velocimetry and Shadow Photography. The heat fluxes were recorded at different distances from the radiation source ranging from 300 to 1000 mm. We have established how the coefficient of heat flux absorption by the water curtain depends on the characteristics of the latter: thickness (100–400 mm), droplet size (10–120 μm), and volume concentration (0.005–0.04 L/m3). The greatest influence on the absorption intensity comes from the total droplet evaporation area. Based on the experimental data, we have developed a physical and mathematical model estimating the impact of scattered radiation on thermal transmittance from the combustion source. Using this model, we have determined the necessary parameters of water curtains, such as length, width, thickness, and droplet size, for the effective shielding of thermal radiation from combustion sources with different heat fluxes.