Experimental Validation of Froude-Modeling-Based Physical Scaling of Water Mist Cooling of Enclosure Fires

Abstract

Fire suppression experiments were conducted in two geometrically similar enclosures of 3-to-1 ratio under fire products collectors to quantify water mist cooling of propane fires, to evaluate the scaling applicability of Froude modeling for water mist cooling of enclosure fires. The parameters considered in the evaluation were: enclosure size, door opening size, water mist spray condition, fire size, fire location and fireshielding condition. The two enclosures measured 1.22x1.22x1.22 m high and 3.66x3.66x3.66 m high. Two door opening sizes were tested for each enclosure: 0.30x0.61 m high and 0.61x0.61 m high for the Scale-1 enclosure and 0.91x1.83 m high and 1.83x1.83 m high for the Scale-3 enclosure. Propane fires were established on 0.3-m and 0.91-m diameter burners respectively for the two scaled enclosures. Four corresponding pairs of propane supply rates were selected according to the scaling requirement, producing 10 to 50 kW at Scale-1 and 150 to 800 kW at Scale-3. Two water mist nozzles operating respectively at 13.8 and 43.7 bar were used to produce the water mist sprays in the two enclosures. In each enclosure, nine nozzles were arranged in a 3x3 pattern at the ceiling level with equal nozzle-to-nozzle and nozzle-to-wall spacing. The results show that Froude modeling can be used to scale water mist cooling of enclosure fires under the present experimental conditions.

Physical Scaling of Water Mist Suppression of Pool Fires in Enclosures

“…Refer to Ref. [14] for a more detailed description of these two enclosures. To evaluate the effect of natural ventilation on fire suppression under water mist application, experiments were conducted with two door opening sizes for each enclosure.…”

“…The Hago 2.25-60P and Hago 20-60P nozzles used in the previous study of water mist suppression of propane fires [14] were employed in the present experiments to produce the water mist sprays in the Scale-1 and Scale-3 enclosures. These two nozzles generated solid-cone sprays.…”

“…Based on the previous experiments conducted with the propane fires [14], it was decided that a fire size with a maximum heat release rate of 20-25 kW be used for the Scale-1 experiments, so the fire would be small enough to be sustained (i.e., not be extinguished by the water mist) but large enough for measurements with the 200 kW FPC. To obtain fire extinguishment results, a larger pool fire was selected with the maximum heat release rate in the range of 45-55 kW.…”

“…Theoretical analysis showed that, under this low Reynolds number condition, the droplet should be scaled with ¼-power of the scale ratio [12], instead of the aforementioned ½-power. The set of scaling relationships with the ¼-power requirement for droplet size has been validated experimentally for water mist cooling of methane fires in open space [13], and water mist suppression of propane fires in enclosures [14].…”

“…[13] and [14], the methane and propane flow rates to the burners were regulated according to the scaling requirement, and maintained constant during each experiment. However, for condensed fuels, the fuel vapor generation is governed by fuel properties, fuel arrangement and fire environment condition, and the latter in turn is influenced by the water mist application and the fire itself.…”