Numerical Study on the Effects of Ambient Air Pressure on Water Mist Characteristics

The effects of ambient air pressure on water mist characteristics were investigated with CFD code FDS6.0. The cases with ambient air pressures of 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5 and 3.0 atm, and water mist operating pressure of 1.5 MPa were considered in the numerical simulation, while the validation experiments were conducted with a single orifice nozzle at normal ambient pressure by using a LaVision Particle-Master Shadow system. The results show that the Sauter mean diameter (D32) of water mist decreased and the droplet velocity increased with the decrease of the ambient air pressure in the same location within the spray. Spray contraction phenomenon occurred where the contraction locations were different under different ambient pressures. Some of the results should be helpful for optimising the water mist fire suppression system.