Structural Features and Smoke Resistance of Water Mist Curtain of Upper Spray Nozzle

Due to its structural limitation, the super-long tunnel faces the difficulty in smoke suppression on the ceiling. For this, the authors aim to develop a water mist curtain with an upward sprinkler head and analyze its smoke suppression performance. FDS numerical simulation was conducted to analyze the changes over time of different parameters such as temperature, smoke spread, radiative heat flux density, CO volume fraction, and the distance between the sprinkler head and the ceiling, and explore the smoke-proof and fire extinguishing effect of the improved water mist curtain together with the tunnel's smoke exhaust system. The results show that with the spray flow rate of 12L/min and droplet size of 300μm, the water mist system with upward sprinkler heads has a more efficient smoke suppression efficiency than the conventional one; the improved water mist system reduced the temperature at the tunnel ceiling by more than 40%, and the CO volume fraction by about 33%, thereby significantly decreasing the smoke density on the ceiling; it reduced the radiative heat flux density at a height of 2m by about 47%, and especially when coupled with the tunnel smoke exhaust system, the smoke suppression performance is better; the smoke volume fraction decreases with the distance between the sprinkler head and ceiling at the height of 5m from the ground. The research findings provide a reference for the smoke suppression of the water mist system and smoke exhaust system in the future.