Assessment of a Method to Enhance the Momentum of Water Mist: Co-Flow Jet Water Mist System

Water mist is considered as a potential alternative to halon in fire extinguishing applications. However, penetration is remarkably reduced due to the rapid decay of momentum in the process of water mist movement, which makes it difficult for water mist to reach the flame zone to extinguish the fire. To effectively improve the momentum of the water mist, a novel water mist system namely co-flow jet water mist system was proposed. A configuration in which a co-flow jet was induced to control the motion of water mist. A three-dimensional simulation was performed on the gas–liquid flow in this system. The Realizable k-e model coupled with the discrete phase model (DPM) was employed for high-speed co-flow jet and laden droplets respectively. Simulations were focused on the interaction of the gas–liquid phase. It was found that the potential core length of the co-flow jet was increased owing to the injection of droplets, but the turbulence intensity and the attenuation of the axial velocity of the co-flow jet were reduced by the broken droplets. In addition, the droplets produced by the atomizer were broken into uniform small ones under the action of co-flow jet, and the spatial distribution of droplets was also changed, more importantly, the momentum of droplets was increased effectively. The droplet size as well as spatial distribution and momentum was related to the gas–liquid mass ratio (GLR). The GLR should be increased as much as possible to enhance the performance of the co-flow jet once the required concentration to extinguish a fire is achieved. This technique is helpful to the popularization and application of a water mist system.