The Characteristics of Fire Smoke Trasport in Channels under Different Ventilation Conditions
|School||University of Science and Technology of China|
|Course||Safety Technology and Engineering|
|Keywords||Channel fires Channel model CO concentration Mechanical exhaust rate Flue gas stratification Flue gas flow rate Smoke layer suction wear Numerical Simulation|
The channel is a typical architectural forms abstract from the traffic tunnel, subway platform channel, underground commercial street construction. With the rapid development of urban construction and tunnel engineering, both at home and abroad has built a large number of channels in the form structure. However, in recent years, occurred in the channel since Qunsiqunshang the disastrous fire accident, caused by the high degree of attention of many researchers of fire safety within the channel. The data indicate that the degree of incomplete combustion within the channel when the fire is very high, which will produce large amounts of toxic gas heat, which is what led to the death. Therefore, the transport properties to study the passage of fire in the smoke under conditions of flue gas is important. Channel, this thesis through theoretical analysis, model experiments to study the natural smoke CO concentration over time the growth characteristics, and use of the experimental data on the distribution of CO concentration and the temperature of the smoke layer in the horizontal direction compared; Then, through model experiments and numerical simulation of the transport properties of the case of transverse mechanical exhaust gas on the horizontal and vertical directions conducted studies to optimize the design recommendations and practical engineering smoke. The specific study includes the following aspects: the previous space distribution of CO concentration, mostly using steady-state concentration value or concentration peak, while ignoring the CO concentration in the space of quantitative growth over time. Some special phenomenon in the transport processes in the papers consider the position of CO along the channel to the distant fire source, the CO concentration in any zone with time any smoke layer within the channel is divided into a number of horizontal segments, through theoretical analysis The growth of the theoretical model and found that the CO concentration in the channel over time in line with growth in the exponent, and carry out experiments to verify the reasonableness of the channel model. The study also found that, through experiments, the CO concentration and temperature distribution in the channel longitudinal direction there is a big difference. Smoke layer in a temperature distribution in the channel longitudinal direction generally tended to decrease, and the concentration of CO in the high position along a channel longitudinal attenuation tendency, in the low position along the channel longitudinal growing trend, resulting in a low position The distant fire source area of ??CO concentrations higher than the area near the fire source. From vertical smoke layer forms at the typical position, the aspects of the flue gas level flow rate and maximum temperature rise, mechanical exhaust rate of the transport properties of the flue gas level to carry out the experimental study. Laser chip optical brightening technology, real-time capture of smoke layer morphology changes with exhaust rate. When the smoke rate is smaller, the flue gas is able to maintain good stratification; With Exhaust rate is gradually increased, the increased flue between the blended layer and air, and the channel end opening near the degree of blending in the distance. By introducing the Froude number, a good explanation of the reasons for differences in blended intensified and the position of the different levels of the smoke layer blending strength. Also found that, as the smoke rate increases, the level of the flue gas flow rate and the maximum temperature rise followed was exponent attenuation law. The smoke layer sucked wear is a special phenomenon in the flue gas in the vertical transport processes, and will lead to the reduction of the mechanical exhaust system performance. In this paper, computational fluid dynamics program of the smoke layer suction wear increases with the exhaust rate of evolution carried out a simulation study, quantitative analysis of the variation of the temperature and thickness of the smoke layer below the exhaust port with exhaust rate. The analysis results show that the presence of smoke layer suction wear rate transition region and completely suck the wear area; channel end opening near the smoke layer thickness changes reflect the The mechanical exhaust efficiency is lowered with the degree of increase of flue gas layer suction wear. Finally, by introducing the concept of the exhaust system output (VSO), based on the experimental data, quantitative analysis of the smoke layer suction wear performance exhaust system, and made recommendations for the project smoke optimization. The results show that, due to the presence of smoke layer suction phenomenon, exhaust system output values ??are always smaller, the output of the exhaust system in the case of the two sources of ignition power (10.4kW and 7.8kW) peak were approximately 36.0% and 17.5%, mostly air exhaust gas through the exhaust port; exhaust rate of increase, under the power of the two sources of ignition system output was to grow first, then gradually decreases until it reaches a stable value, respectively. approximately 12.5% ??and 7.5%.