Study On Exhaust Effect Of Subway Tunnel With Length-width Ratio Of Shaft With Nature Ventilation

Natural ventilation is a possible means of technical measures in order to save theenergy consumption of the subway tunnel ventilation by metro operation at the topopening of the metro tunnel. There is a very important issue in the design of subwaytunnel disaster prevention how to exhaust smoke effectively in order to ensure the safetyof evacuation if the train fire in the tunnel with the natural ventilation. In this paper, thesmoke spreading of the metro tunnel with natural ventilation mode under the differentlength-width ratio of shaft was analyzed and simulated by use of model fire test and firedynamics software FDS.The shrunken size subway Tunnel model with the ratio of1:15consisting ofinterval tunnel and exhaust duct was installed according to Froude-number Model,While the test of the shaft at different length-width ratio, the tunnel smoke temperaturedistribution were measured and flue gas flow pattern was observed.The experimental results showed that: the temperature of smoke in the areabetween the two natural ventilation shafts near the fire source is higher than others.Smoke mainly discharged through the recent natural ventilation shaft of the side nearthe fire source, followed that the temperature are reduced rapidly; the smoke effectwhen the length-width ratio of shaft is10than2.5and5is more favorable.While using the fire dynamics simulation software FDS to establish full-size metrotunnel model corresponding to the model test was simulated flue gas flowcharacteristics of the different length-width ratio of shaft, the simulation results showthat: the error between numerical results and model test results is small, indicating thatFDS can be used for numerical simulation analysis in the subway natural ventilation tunnel fire.I obtained four parameters of the tunnel fire environment through the analyzedcontrol standards of the safety of evacuation when the train fire in the tunnel: Thesmoke temperature at human eye height in the tunnel is not more than66℃; COconcentration at human eye height in the tunnel is not more than250ppm; visibility athuman eye height in the tunnel is not more than8.4m; the tunnel roof wall smoketemperature away from sources of ignition30m is not more than150℃. Combined withfour parameters to control the fire environment we analyzed the characteristic of theflue gas flowing and the human safety of evacuation, when fire heat release rate is10MW, the shaft spacing is30m, the shaft height is4m, the shaft area is32m2, thelength-width ratio of shaft is5~7.5the smoke effect is more favorable.