UTILIZATION OF FINE WATER SPRAYS IN EXPLOSION MITIGATION: COLD TRIAL

Abstract

For the past fifty years, there has been a great deal of interest using water-based explosion suppression systems in mitigating/reducing the impact of thermal explosions and their consequential overpressures. Previous research focused on the suppression and mitigation with sprays containing droplets 200µm ≤ D32 ≤ 1000µm. The present study is focused on the mitigation of slow-moving deflagrations with speeds of less than or equal to 30 m/s. Consequently, the droplets within the spray must be small enough to extract heat in the short finite moments that the flame and droplets interact at about 0.03 ms for a 1 mm thick flame front. An apparatus was thus designed to simulate ‘partly confined and/or vented’ conditions, venting upstream of the propagating flame. Previous theoretical studies have suggested that droplets in the order of 10 µm to 20 µm will enable to mitigate combustion without relying on further droplet break up. This investigation, herewith, is presenting the full details of qualitative and quantitative analysis of using Spill Return Atomiser (SRA) to provide fine water spray. The spray cone angle was increased from 34.7˚ to 49.2˚and the exit orifice flow rate was raised from 0.295 l/min to 1.36 l/min. Increasing the flow rate provided a number of spray options ranging from 17µm ≤ D32 ≤ 29µm, with liquid volume flux of 0.011 cm³/s/cm² to 0.047 cm³/s/cm² and mean droplet velocity of 0 to 21.4 m/s, with the resulting of complete explosion mitigation qualities.