Critical velocity in point extraction for dual longitudinally ventilated tunnel fire

2022 ◽  
Vol 122 ◽  
pp. 104313
Author(s):  
Xuepeng Jiang ◽  
Juan Wan ◽  
Zhengyang Wang ◽  
Meijia Liu
Keyword(s):  
Critical Velocity ◽  
Tunnel Fire

scholarly journals Critical velocity analysis for safety management in case of tunnel fire

2020 ◽  
Vol 305 ◽  
pp. 00023
Author(s):  
Omar Lanchava ◽  
Nicolae Ilias
Keyword(s):  
Critical Velocity ◽  
Critical Speed ◽  
Safety Management ◽  
Combustion Products ◽  
High Heat ◽  
Velocity Analysis ◽  
Critical Number ◽  
Effective Management ◽  
Tunnel Fire ◽  
Underground Fire

Heat, smoke and other toxic products may spread along the tunnel, in both directions from the seat of fire, causing different kinds of damage to people. Anyway, underground fire causes complicated results, which is preventing factor for life rescue and evacuation, creating difficulties for firemen and life rescue crew. Analysis of the critical speed, which is necessary for the effective management of combustion products, has been made for tunnel fires with high heat release rate. The characteristic changes in the critical Froude number in the work are presented in accordance with the critical speed. Particularly, it was noted that the formula determining the critical speed requires knowledge of the average smoke temperature, while the formula for calculating the last value includes the value of the required critical speed. In order to overcome this, Froude’s critical number Frc=4.5 has been introduced, which is not the way of solution, as it directly means constant critical velocity for the fire of any power and accordingly, does not correspond to experimental data.

scholarly journals Simulation Study on Critical Velocity of Longitudinal Ventilation Tunnel Fire

2013 ◽  
Vol 52 ◽  
pp. 67-71 ◽  
Author(s):  
Jun Deng ◽  
Li Ma ◽  
Zhen-ping Wang ◽  
Zhen Xing ◽  
Wei-feng Wang
Keyword(s):  
Critical Velocity ◽  
Simulation Study ◽  
Tunnel Fire ◽  
Longitudinal Ventilation

Numerical Simulation and Analysis of Critical Velocity in Tunnel Fires Based on FDS

2013 ◽  
Vol 831 ◽  
pp. 455-459
Author(s):  
Shu Hui Xu ◽  
Ling Fei Cui ◽  
Lei Ning ◽  
Zi Ye Wang
Keyword(s):  
Heat Release ◽  
Critical Velocity ◽  
Heat Release Rate ◽  
Release Rate ◽  
Small Scale ◽  
Smoke Control ◽  
Tunnel Fires ◽  
Tunnel Fire ◽  
Velocity Prediction ◽  
The One

Critical velocity is a very important parameter in smoke control of tunnel fires and the variation of critical velocity against fire heat release rate is also one of the most important issues in tunnel fire researches. In this paper, a simplified physical model of a tunnel was established and the predictions of critical velocity for fire sizes in the 5-100MW range were carried out by FDS simulations. The FDS-predicted dimensionless critical velocities were compared with the values calculated by Wu and Bakar’s model. The result indicated that when the heat release rate was relatively small, Q≤30MW, the critical velocity increased with the increasing of heat release rate and varied as the one-third power of the heat release rate; when Q≥40MW, the growth rate of critical velocity became very small; after Q reach to 60MW, the critical velocity was almost unchanged with the increasing of heat release rate. In addition, the values of critical velocity calculated by Wu and Bakar’model which was derived from small-scale gas fire tests were underestimated. Therefore, the model suggested by Wu and Bakar is not suitable for critical velocity prediction in tunnel fires.

scholarly journals Numerical Investigation of Critical Velocity in Reduced Scale Tunnel Fire with Constant Heat Release Rate

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Ruben Mouangue ◽  
Philippe M. Onguene ◽  
Justin T. Zaida ◽  
Henri P. F. Ekobena
Keyword(s):  
Heat Release ◽  
Critical Velocity ◽  
Heat Release Rate ◽  
Release Rate ◽  
Combustion Products ◽  
Healthy Environment ◽  
Tunnel Fire ◽  
Air Supply ◽  
Minimum Velocity ◽  
Reduced Scale

When a fire occurs in a tunnel in the absence of sufficient air supply, large quantities of smoke are generated, filling the vehicles and any space available around them. Hot gases and smoke produced by fire form layers flowing towards extremities of the tunnel which may interfere with person’s evacuation and firefighter’s intervention. This paper carries out a numerical simulation of an unexpected fire occurring in a one-way tunnel in order to investigate for the critical velocity of the ventilation airflow; this one is defined as the minimum velocity able to maintain the combustion products in the downstream side of tunnel. The computation is performed successively with two types of fuels representing a large and a small heat release rate, owing to an open source CFD code called ISIS, which is specific to fires in confined and nonconfined environments. It is indicated that, after several computations of full-scale fires of 43.103 and 19.103 kJ/kg as heat release rate, the velocities satisfying the criterion of healthy environment in the upstream side of the tunnel are 1.34 m/s and 1.12 m/s, respectively.

Effects of ambient pressure on the critical velocity and back-layering length in longitudinal ventilated tunnel fire

2019 ◽  
Vol 29 (7) ◽  
pp. 1017-1027
Author(s):  
Guanfeng Yan ◽  
Mingnian Wang ◽  
Li Yu ◽  
Yuan Tian
Keyword(s):  
Heat Release ◽  
High Altitude ◽  
Critical Velocity ◽  
Heat Release Rate ◽  
Release Rate ◽  
Ambient Pressure ◽  
Smoke Movement ◽  
Tunnel Fire ◽  
Longitudinal Ventilation ◽  
High Altitude Area

Nowadays, the critical velocity and back-layering length are the key parameters in longitudinal ventilation design. However, most studies research them at standard air pressure but ambient pressure decreases at high-altitude area and the reduced ambient pressure could affect the smoke movement characteristics in a tunnel fire. In order to investigate the effect of ambient pressure on the velocity and back-layering length in longitudinal ventilated tunnel, theoretical analysis was carried out first and a series of numerical simulation were conducted with varying heat release rate and ambient pressure. Results show that Li’s model is also reliable under various ambient pressures. The critical velocity under various ambient pressures would become larger with an increase in the heat release rate and would remain stable after the heat release rate reaches a certain value. At smaller heat release rate, the length of counterflow would be higher under reduced ambient pressure while it remains the same when the HRR is large. This could provide reference for tunnel ventilation design at high-altitude areas.

scholarly journals Review of Research on critical velocity in tunnel fire

2019 ◽  
Vol 79 ◽  
pp. 02001 ◽  
Author(s):  
Gui-hong Pei ◽  
Qiu-yi Zhang
Keyword(s):  
Influencing Factors ◽  
Critical Velocity ◽  
Release Rate ◽  
Fire Spread ◽  
Fire Control ◽  
Fire Source ◽  
Tunnel Fire ◽  
Longitudinal Ventilation ◽  
Tunnel Section ◽  
Ventilation Velocity

The critical velocity is the key for tunnel fire control. If the longitudinal ventilation velocity is greater than the critical velocity when the fire occurs, the upstream of the fire source is smokeless, and the smoke will flow to the downstream of the fire source, which can effectively control the fire spread and provide valuable time for personnel to escape and fire fighting. The researches of domestic and foreign scholars are used to investigate the influencing factors of critical velocity. the results show that the main influencing factors of critical velocity are fire heat release rate, tunnel section geometry, obstacle and slope in tunnel, etc. In this paper, the influencing factors are summarized, and some problems that need to be studied in tunnel fire are put forward.

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