Experimental research on the water mist fire suppression performance in an enclosed space by changing the characteristics of nozzles

• The cover area and droplet size of nozzles increase with spray cone angle.
• Extinguishing time increases with spray cone angle, and decreases with flow rate and supply pressure.
• More time exceeding a certain value for water mist discharge duration is not helpful to the cooling.
• Gas concentrations are not affected by the water mist discharge duration if it exceeds the extinguishing time.
• The flow rate and spray cone angle should match mutually, in order to maximize the utilization of water.

Water mist is an ideal way in enclosed spaces, where fire suppression efficiency is very important due to limited water and water damage to equipment. The purpose of this paper is to find a more effective way of fire suppression performance by changing characteristics of nozzles, taking into account extinguishing time, water consumption, toxic gas concentration, temperature decay and cover area. Two groups of pressure-swirl nozzles with the same flow rate and different spray cone angles were employed. The angle was adjusted by changing diameters and lengths of entrance, swirl chamber and orifice of nozzle. It was found that the cover area and the droplet size increased slightly with the spray angle. The fire tests results showed that the extinguishing time increased with the spray cone angle, and increased with the flow rate and the operating pressure decreasing. The temperature decay rate was improved by decreasing the angle or increasing the flow rate. In addition, with an increase in the extinguishing time, the concentration of O2 decreased while the CO and CO2 increased. However, the gas concentrations were not affected by the water mist discharge duration if it exceeded the extinguishing time. For a specific region and a certain amount of water, the performance can be improved by the approach: increasing the flow rate and the spray angle simultaneously and decreasing the discharge duration. The authors suggest setting proper flow rate and spray cone angle which match mutually, in order to maximize the utilization of water.