Influence of ambient pressure on critical ventilation velocity and backlayering distance of thermal driven smoke in tunnels with longitudinal ventilation

Guo, Fangyi; Gao, Zihe; Wan, Huaxian; Ji, Jie; Yu, Longxing; Ding, Long

doi:10.1016/j.ijthermalsci.2019.105989

Cited by 46 publications

(11 citation statements)

References 23 publications

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“…Then, the size of the finest mesh for a 2-4 MW fire was calculated to be between 0.07 and 0.4 m. Obviously, the finer grid will better reflect the heat flow field in detail, but it is also time-consuming. The mesh grid size was chosen to be 0.167 m in this study, which corresponds with previous studies [2,21,22]. To further verify the accuracy of the LES model, the vertical temperature distributions inside the staircase without external wind are compared with previous research [9,23], as shown in Figure 2.…”

Section: Numerical Modelingmentioning

confidence: 99%

Smoke Back-Layering Phenomenon under the Combined External Wind and Stack Effects in a Staircase

Wang

Chen

et al. 2022

Applied Sciences

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The external wind can change smoke movement patterns inside the staircase and affect smoke exhaust efficiency. This paper analyzes the smoke back-layering phenomenon in the staircase with open stair doors below the fire floor. The effect of the open stair door location and the heat release rate of fires and external wind velocities on smoke movement patterns are investigated numerically. The external wind ranges from 0–5.5 m/s. At 0 m/s, the smoke back-layering phenomenon driven by pressure difference can be found in the staircase with all stair doors closed. With the increasing wind velocity, four smoke behaviors are identified: upward moving smoke, first downward then upward moving smoke, downward moving smoke, and no smoke. Results show that the back-layering distance is mainly influenced by the external wind and heat release rate of fires. Correlations are modified and used to predict the longest back-layering distance with the first downward then upward moving smoke. This helps with arranging the smoke detectors inside a staircase and the fire safety design of high-rise buildings.

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Section: Numerical Modelingmentioning

confidence: 99%

Smoke Back-Layering Phenomenon under the Combined External Wind and Stack Effects in a Staircase

Wang

Chen

et al. 2022

Applied Sciences

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“…In view of this, the temperature decay can be approximated using an exponential function [20,40]. Li et al [43] found that the form of the sum of two exponential functions, that is ∆T(x)/∆T max = a × exp b× x H +c × exp(d× x H , can well describe the decay of temperature under the tunnel ceiling.…”

Section: Of 16mentioning

confidence: 99%

“…Taking the average value of each coefficient, the empirical formula of temperature attenuation under the tunnel ceiling with four smoke vents open can be obtained as follows: To highlight the difference between the single-side multi-point exhaust tunnel and the previous research results, we compared the temperature attenuation model in this paper with some existing temperature attenuation models. Ji et al [37] studied the effect of pressure and HRR on the temperature decay beneath the ceiling and found that the impact of pressure on temperature decay is very small, and the temperature attenuation conforms to the sum of two exponential attenuations: Ingason and Li [43] concluded that the temperature attenuation beneath the ceiling conforms to the sum of two exponential attenuations:…”

Section: Of 16mentioning

confidence: 99%

Effect of Different Smoke Vent Layouts on Smoke and Temperature Distribution in Single-Side Multi-Point Exhaust Tunnel Fires: A Case Study

Tao

Zeng

2022

Fire

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In this paper, a numerical model verified by a 1:10 small-scale model test was used to study the effect of different smoke vent layouts on fire characteristics and smoke exhaust efficiency. The results show that the total smoke spread length is shortest when four smoke vents are opened near the fire source. If there are more than four smoke vents, some of them will only inhale fresh air rather than smoke. More seriously, some smoke vents will promote the spread of toxic smoke farther. Under different smoke vent layout schemes, the maximum temperature shows the same change trend with the increase in smoke exhaust volume (first increasing and then decreasing). When there are four smoke vents, the temperature field is in a good range compared with other schemes. If four smoke vents are opened, the total smoke exhaust efficiency is highest, and exhaust rate has little influence on total exhaust efficiency. Total smoke exhaust efficiency of the tunnel is more than 93.7% under different exhaust volumes, and the maximum difference of total smoke exhaust efficiency is less than 1.5% under different exhaust volume of Case “4”. The exhaust volume has little influence on temperature decay beneath the ceiling, and a temperature attenuation model of a point exhaust tunnel with four smoke vents was proposed. For the single-side point exhaust tunnels, the number of smoke vents near the exhaust fan side shall not be more than that on the other side. Four smoke vents shall be opened in case of fire and the exhaust volume is 220 m³/s with HRR of 30 MW.

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“…Following these studies, many researchers have studied the effects of several other factors on the back-layering length, and proposed a series of new prediction models, such as tunnel slope [9], cross section [10], turning radius [11], ceiling extraction [12][13][14], branched tunnel [15], and ambient pressure [16][17][18].…”

Section: Hmentioning

confidence: 99%

Effect of the Metro Train on the Smoke Back-Layering Length under Different Tunnel Cross-Sections

et al. 2022

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Smoke back-layering length is an important aspect of tunnel fire research, and the influence of metro train blockage cannot be ignored. In previous studies, less attention has been paid to the phenomenon of back-layering caused by the same train blocked in tunnels with different cross-sections. This paper investigates this point through dimensionless analysis and fire dynamic simulator (FDS) numerical simulation. Several full-scale model tunnels (300 m in length), with different tunnel cross-sections, were constructed in FDS. According to the FDS simulation result, the smoke back-layering length was compared and analyzed. To investigate the effect of the tunnel cross-sections on smoke back-layering length under metro train blocking, the headroom ratio ε was proposed. Then, the influence of the tunnel cross-section on the smoke back-layering length was discussed in detail. Based on the dimensional analysis and FDS simulation results, a new model for predicting the smoke back-layering length was proposed. The prediction model obtained in this paper was compared with the FDS simulation results and the prediction model proposed by our predecessors. It is proven that the proposed model can better predict the length of smoke back-layering when metro trains are blocked in tunnels with different cross-sections. The outcomes of this work are expected to provide theoretical guidance for fire smoke control in metro tunnels with different cross-sections.

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Influence of ambient pressure on critical ventilation velocity and backlayering distance of thermal driven smoke in tunnels with longitudinal ventilation

Cited by 46 publications

References 23 publications

Smoke Back-Layering Phenomenon under the Combined External Wind and Stack Effects in a Staircase

Smoke Back-Layering Phenomenon under the Combined External Wind and Stack Effects in a Staircase

Effect of Different Smoke Vent Layouts on Smoke and Temperature Distribution in Single-Side Multi-Point Exhaust Tunnel Fires: A Case Study

Effect of the Metro Train on the Smoke Back-Layering Length under Different Tunnel Cross-Sections

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