Abstract
Some phenomena of spray dynamics of water mist for fire suppression are studied numerically. The transport of fine mist sprays is very different than that of the typical large water sprinkler drops because water mist may have a better ability to follow the air streams and to penetrate into hidden locations behind obstructions or through opening slots where fire occurs. First, the free falling of fine droplet in stagnant air is examined to reveal the time delays and change of volumetric number density of the spectrum of droplets. Then, the 2-D numerical simulations of a two-phase gas droplet flow based on Navier-Stokes equations are performed to study the motion of droplets around a rectangular strip obstruction. The deposition of the droplets on the strip and the flow around the strip are investigated. The collection efficiency on the strip is computed numerically as a function of the inertial impaction parameter. In addition, flow over a single strip in a domain with various widths is also examined to reveal the characteristics of the flow over an array of repeated strips. No major variation on the collection efficiency with respect to the single strip is observed if the blockage fraction (B), which is the fraction of the size of strip to the total width of the flow domain, is less than about 0.33. The penetration efficiency of the mist droplets through an array of slots can be evaluated based on the collection efficiency and the geometric fraction of the strip to the flow domain configuration.
