Experimental Study On Suppression Of Liquid Pool Fire With Water Mist Under Longitudinal Ventilation In Long And Narrow Spaces

The increasing development of the buildings of long and narrow space, like tunnels, brings lots of new problems to the fire protection with the convenience brought to daily life. Meanwhile, with the development of science and technology, the higher requirement for protecting the long and narrow space from fire is put forward by society. Water mist is used widely for suppressing fires in the long and narrow space like traffic tunnels and cable tunnels, due to no pollution, high fire extinguishing effectiveness, safety to human and equipment, less water consumption, etc. However, the study on fire suppression with water mist on the condition of ventilation in long and narrow space is lagging behind. Therefore, the longitudinal ventilation, a typical ventilation mode of long and narrow space, is chosen in the paper. And the mechanism of liquid pool fire suppression with water mist on the condition of longitudinal ventilation in the long and narrow space is investigated systematically.A small-scale experimental bench of long and narrow space, whose dimension is 5.5m X 0.9m X 0.6m, was established. And the airflow distribution characteristics was measured and then corrected. The water mist field measurement was performed through three-dimensional LDV/APV system and DPIV technology on the windless and longitudinal ventilation condition, respectively. Then longitudinal ventilation's influence on the water mist field was analyzed theoretically based on the above experimental results.Available small wind tunnel for combustion was modified, and the experimental study on the combustible characteristics of liquid pool fire on the condition of longitudinal ventilation was closely performed in the wind tunnel. According to the conservation of energy, the combustion processes of different typical liquid pool fires on the condition of longitudinal ventilation were compared and the rule of their burning rates'changes with longitudinal wind velocities was proposed and the ventilation's acceleration effect on their burning rates was analyzed. The experimental study on longitudinal wind velocities'influence on the ethanol evaporation rates on the different conditions of radiation intensity in the wind tunnel was performed, and the experimental measurement of thermal feedback characteristics on the different conditions of ventilation velocities was carried out, and based on which, the mechanism of longitudinal wind velocities'influence on the burning rates of ethanol pool fires was discussed.Based on the model for predicting the critical ventilation velocity on the condition of no water mist and the conservation of energy in the field of fire, the critical prediction model on the condition of water mist was established. The experimental study on critical ventilation velocities with or without applying water mist in the long and narrow space was carried out. And the results without water mist was compared with the value predicted based on the previous predict models, and the coefficient in the model for predicting the critical ventilation velocity without water mist was fitted according to the measurement results. On this basis, the accuracy of the model for predicting the critical ventilation velocity with water mist was verified by combining the measured critital longitudinal ventilation velocity and the heat-absorbing calculated value by water mist. We still performed the experimental study on critical ventilation velocities on the condition of different positions where water mist was sprayed, and analyzed the positions' influence on the critical longitudinal ventilation velocity according to the experimental results, and discussed the mechanism of the water mist's influence on the critical longitudinal ventilation velocity.Experiments of n-heptanes pool fire suppression with water mist on the condition of longitudinal ventilation was performed closely using the simulated test bench of long and narrow space. The extinguishing effectiveness with water mist on the different conditions of longitudinal ventilation velocity was studied by way of changes of oil pool fire's pre-ignition time, working pressure for water mist, the position where the water mist was sprayed and longitudinal ventilation velocity. And the longitudinal ventilation velocity's influence on the extinguishing performance with water mist was discussed. Then,the factors of fire suppression with water mist on the condition of longitudinal ventilation were studied by combining the results of the water mist field measurement on the condition of longitudinal ventilation, the fuels' temperature on the different condition of wind speed, the results of smoke concentration around the fire and the fire morphology in the extinguishing process, thereby the mechanism of wate mist suppressing n-heptane pool fire was revealed.