Experimental And Applied Studies On Characteristic Of Smoke Blockage By Water Mist Screens In Long And Narrow Spaces Fires

In fire accidents,high temperature smoke is the main factor that causes casualties.The effective smoke control can provide protection for evacuation and rescue.It is a new way to control and exhaust smoke in a separated area by using water mist in long and narrow space.The function of water mist is transformed from fire extinguish to smoke control.Using water mist in such space has great practical significance and engineering application value for smoke control.To verify the validity of the method and reveal the phenomenon of the blocking fire-induced smoke by water mist in a long tunnel,theoretical analysis,scaled model experiments,and numerical simulation were carried out.The specific work includes:Aiming at the control of smoke in a narrow space,this paper puts forward the smoke control method by water mist type's curtain.By drawing on the experience of industrial wet dedusting theory,analyzing the mechanism of the blocking fire smoke by water mist screen,the formula for calculating the smoke elimination efficiency of water mist was obtained and a mathematical model of the interaction between water mist and smoke was established.According to the formula,the analysis results show that water mist droplet diameter,injection pressure and width of the screen are the main parameters affecting the efficiency of water mist eliminating smoke.The efficiency increases by reducing the particle size of water,improving the injection pressure and raising the width of the water mist screen.Taking a narrow channel as a prototype,a 1:3 long and narrow space test-bed model was established according to Froude similarity criterion,which was 8.5 m long,1.2 m width,and 1.7 m high.At the same time,a set of high pressure water curtain system of single fluid was designed.The characteristics of water mist field,such as droplet size distribution,velocity distribution,spray cone angle,and fog flux,were measured by PDA.The mist flux was measured by collection method.These results provide equipment support for the further development of water mist screen smoke insulation performance.Fifteen fire tests about flow characteristics of smoke in a long and narrow space were carried out on the test-bed model.The smoke control effectiveness of a water mist screen in the long channel was qualitatively observed.The influence of spray pressure,width of the water mist screen,spray angle and mechanical smoke exhaust and other factors on the smoke resistance performance of the water mist screen were quantitatively analyzed.By monitoring the temperature,O₂,CO₂ and CO concentration,illumination variation,the effects of spray pressure,water curtain width,spray angle and mechanical smoke exhaust on the performance of water mist curtain wall were quantitatively analyzed.The experimental results show that in the narrow space setting water mist type's water curtain can be seen as compartmentation,which is conducive to the improvement of downstream evacuation condition.The experimental results also provide data support to the theoretical model of smoke control method,numerical simulation and engineering application parameter design.Whether the smoke spread can be effectively blocked by water mist can be accurately predicted by means of CFD simulation.It is important to make the comparison of simulation results to experimental observations.The results reveal that FDS can reconstruct the experimental observations successfully.Based on the success of the simulations,research ideas and simulated tools were provided for the study of water mist screen and transverse ventilation?WMSTV?system in tunnel fires.Based on long and narrow space tunnel's experimental and theoretical study on the water mist screen,coupling method water mist screen and central exhaust smoke control method?WMSTV system?was proposed.Taking a tunnel project as an example,the numerical simulation study was carried out.The feasibility of the method was verified by the simulation analysis of 16 working conditions,and the engineering design parameters are given.Taking into account the distance between the emergency evacuation of the tunnel,the water mist spacing can be selected 120 m,150 m or 180 m for smoke compartment.When the compartment length is 120 m or150 m,two exhaust vents should be arranged in the area.When the compartment length is 180 m,four exhaust vents should be arranged.The minimum distance of two exhaust vents is between 40 m and 60 m;the distance between the exhaust vent and the water mist should be between 30 m and 45 m.Finally,the fire fighting strategy under the control of the WMSTV system can be obtained according to the simulation results.