2019 Volume 61 Issue 198 Pages 361-367
Indirect fire extinguishment was carried out by causing water droplets of a size of a few millimeter order to collide with a heated solid plate. We focused on the difference in the surface roughness of the heated plate and investigated the fire extinguishing characteristics experimentally. The evaporation characteristics of the droplet is related to the flame extinguishing probability. The coarser the solid surface roughness, the higher the Leidenfrost point moved to the higher temperature side, and the nucleate boiling region expanded. As a result, even when the solid surface temperature was high, steam and mist were sufficiently generated and fire extinguishment became possible. The spreading width of water vapor and mist was smaller as the solid surface roughness was coarser. In addition, the direction of its movement changed from the horizontal direction to the vertical direction as the solid surface roughness became coarse. This was related to the spreading behavior of the liquid film on the solid surface after droplet collision.