Experimental demonstration of enhanced radiative shielding performance induced by Mie scattering of fine water-mist particles

The use of water mists is an alternative protection method against the thermal radiation of fires. However, the shielding effectiveness depends on droplet diameter, droplet number density, and optical path thickness. In this study, we combine controlled experiments with radiative transfer analysis to quantify the droplet-diameter dependence of transmittance in microscale water mists with Sauter mean diameters ranging from 5 to 20 μm. A physically grounded, diameter-dependent scaling factor is introduced to predict the measured transmittance across various operating conditions. Droplet size distributions are obtained using laser diffraction particle size analysis. In addition, the droplet number density and mist-layer thickness are estimated from particle image velocimetry–derived velocity fields together with flow-rate constraints. The transmittance between a blackbody furnace at 1200 K and an infrared power meter is measured at multiple stand-off distances. These measurements are subsequently compared with predictions from those obtained through a ray emission model coupled with Mie scattering theory. The diameter-dependent scaling factor inferred from the experiments agreed with that computed by the radiative transfer analysis. Moreover, finer droplets yielded stronger attenuation per unit optical thickness, clarifying how droplet diameter sets the leading-order transmittance when the number density and path thickness are known. • Radiative shielding performance of water mist experimentally investigated. • Laser diffraction and PIV used to measure droplet size and volume fraction. • Normalized shielding factor represents the importance of finer droplets.