Effect of low ambient air pressure on spray characteristics of water mist

• Effects of low ambient pressure on characteristics of water mist were investigated.
• The Sauter mean diameter of water mist decreases with decrease of ambient air pressure.
• Axial velocities of droplets under higher working pressure decrease with decrease of air pressure.
• The radial velocities of water mist increase with decrease of ambient air pressure.
• An empirical formula was determined to correlate droplet size and ambient air pressure.

To investigate the effect of low ambient air pressure on the characteristics of water mist which was injected into a low pressure (<0.1 MPa) environment, the sizes and velocities of the water droplets were measured using Shadowgraph technique. A stainless steel vessel with a diameter of 600 mm and height of 800 mm was designed for simulating low ambient air pressure conditions using a vacuum pump. Ambient air pressures of 0.1, 0.08, 0.06, 0.04, 0.02 MPa, and working pressures of the water mist system of 1.0, 3.0, 4.0 MPa were considered. The results show that, under each certain pressure of water mist system, both of the Sauter mean diameter (d32) and the arithmetic mean diameter (d10) of water mist droplets decrease with decrease of the ambient air pressure from 0.10 to 0.02 MPa. An empirical formula has been developed to express the influence of ambient air pressure on Sauter mean diameter of water mist. In addition, the axial velocities of water mist droplets generated with working pressure of 3.0 MPa and 4.0 MPa decrease following a decrease in ambient air pressure, while there is no obvious variation to the tested results of the cases with 1.0 MPa working pressure.