Experimental investigation on the dynamics of a single water droplet impacting wood surface

Abstract

The dynamic characteristics of water mist droplets hitting the wood surface is one of the important factors affecting the fire extinguishing performance. However, the spreading dynamics between water droplets and wood surfaces during the impacting process have not been adequately characterized in existing literature. This study experimentally investigates the dynamic process of a single water droplet with changing Weber numbers from 66.7 to 1268.5 impacting different solid wood surface from the perspective of fire suppression. Typical impacting phenomena, the phenomena distribution, the droplet spreading dynamics and the maximum spread factor have been analyzed and discussed. Typical phenomena including no splash, transition from no splash to prompt splash, and prompt splash with varying Weber number are observed for the wood surface. The typical phenomena distribution can be distinguished by lgWe and lgRe and the result shows that lgWe < 2.11, 2.11 < lgWe < 2.42, and lgWe > 2.42 correspond to the phenomena of no splash, transition from no splash to prompt splash and prompt splash respectively. The spreading time can be predicted by the expression of ts/(ρRmax3/σ)0.5=6.52∗We-0.92. By analyzing the maximum spreading factor, the model βmax∝(We/Oh)0.198 is found to present good predictions for wood surfaces.