# Numerical Simulation on Smoke Temperature Distribution in a Large Indoor Pedestrian Street Fire

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## Abstract

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## 1. Introduction

## 2. Numerical Simulation Parameter Setting and Experimental Verification

#### 2.1. Introduction of PyroSim

#### 2.2. Commercial Pedestrian Street Experiment

^{3}/h.

^{2}, 95% ethanol was selected as fuel, 16 L was injected for each test. Cooling water was injected into the water-bearing plate to ensure the test safety, and the combustion plate will not float. Ammonium chloride smoke cake was selected as the smoke generating material for the test. The smoke generated by combustion was guided to the top of the fire source through an independent smoke generator. The tracer smoke was neutral, white, and basically free of residue.

#### 2.3. Model Parameter Setting

^{2}fast fire. The simulated initial temperature was 20 °C. The simulation time was consistent with the experimental time, and all doors and windows were kept closed.

#### 2.4. Grid Independence Analysis

_{x}is given in the FDS Operation Manual [16], and δ

_{x}is the nominal size of the grid cell. Its definition formula is as follows:

^{2}; ρ

_{0}is the ambient air density, 1.29 kg/m

^{2}; c

_{p}is the specific heat capacity at constant pressure, 1.005 kJ/(kg∙K); T

_{0}is the ambient air temperature, 293 K. Taking the heat release rate of 1.5 MW as an example, the characteristic size of the fire is D* = 1.09 m. It is generally believed that when the ratio of characteristic diameter to grid is 4~16, the simulation results are more accurate, that is, the grid size is 0.27~0.06 m. Due to the large volume of the physical model, the grid size of the atrium is assumed to be 0.3 m, which basically meets the operation conditions.

#### 2.5. Experimental Verification of Numerical Simulation Results

_{α}(r − 1, n − r) [17]. The calculation results of analysis of variance are shown in Table 2.

## 3. Analysis and Discussion of Numerical Simulation Results

#### 3.1. Analysis of Smoke Spread in Atrium Fire

#### 3.2. Vertical Smoke Temperature Distribution in Atrium

^{2}; $\dot{Q}$ is the heat release rate of the fire, kW; z is the height, m; ${T}_{\infty}$ is the ambient temperature, 293 K. The three zones of the axisymmetric buoyant plume are shown in Figure 13. The values of κ and η of the McCaffrey plume model are shown in Table 3.

#### 3.3. Horizontal Smoke Temperature Distribution under the Ceiling of the Atrium

## 4. Conclusions

- (1)
- After a series of comparative studies, it is found that the conclusions obtained from the numerical simulation study and the full-scale experimental study are in good agreement. The smoke spread rate increases with the increase of the heat release rate of the fire source, and the thickness of the stable smoke layer increases as well. When the smoke exhaust system is turned on, the smoke volume decreases rapidly, the smoke layer thickness decreases and the visibility increases.
- (2)
- The higher the heat release rate of the fire source, the higher the average temperature of the smoke in the atrium. There exists an obvious stabilization phase of the smoke temperature. When the smoke exhaust system is turned on, the smoke temperature decreases and the stabilization phase of the smoke temperature is shortened. In the actual scenario, the effect of multi-system cooperative smoke exhaust is better than the smoke exhaust effect of single smoke exhaust system. The smoke temperature distribution obtained from the numerical simulation agrees well with the modified McCaffrey plume model.
- (3)
- The horizontal dimensionless smoke temperature rise below the atrium ceiling changes exponentially with the dimensionless distance from the fire source. The greater the heat release rate, the greater the smoke mass flow rate and smoke spread rate, and the smaller the attenuation coefficient. The attenuation coefficient increases when the smoke exhaust system is turned on. Furthermore, this indicates that the effect of mechanical smoke exhaust is better than that of natural smoke exhaust. Among the factors related to the attenuation coefficient, the effect of the heat release rate of the fire is stronger than that of smoke exhaust. In practical applications, using low calorific value materials, reducing the stacking of combustibles and adjusting the exhaust mode and volume all contribute to the increase of the attenuation coefficient to decrease the atrium temperature as soon as possible.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 2.**Schematic diagram of fire source layout of different heat release rates (1.5 MW, 0.7 MW, 0.34 MW, from left to right).

**Figure 5.**Comparison of temperature change between experiment and numerical simulation of measuring point 1 in Case 1.

**Figure 7.**Temperature variation of measuring points at different heights above the atrium in Case 1.

**Figure 8.**Temperature variation of measuring points at different heights above the atrium in Case 2.

**Figure 9.**Temperature variation of measuring points at different heights above the atrium in Case 3.

**Figure 10.**Temperature variation of measuring points at different heights above the atrium in Case 4.

**Figure 11.**Temperature variation of measuring points at different heights above the atrium in Case 5.

**Figure 12.**Variation of vertical smoke average temperature in atrium with height from fire source center in Cases 1~5.

**Figure 15.**Variation of dimensionless smoke temperature rise $\Delta T/\Delta {T}_{0}$ under atrium ceiling with dimensionless distance from fire source x/H in Cases 1~5.

Case | Heat Release Rates | Fire Location | Smoke Exhaust Mode |
---|---|---|---|

Case 1 | 1.5 MW | Atrium 2# | natural filling |

Case 2 | 1.5 MW | Atrium 2# | natural smoke exhaust |

Case 3 | 0.7 MW | Atrium 2# | natural filling |

Case 4 | 0.34 MW | Atrium 2# | natural smoke exhaust |

Case 5 | 0.34 MW | Atrium 2# | mechanical smoke exhaust |

Error Source | Sum of Squares | Freedom | Mean Square | F | F_{α}(r − 1, n − r) |
---|---|---|---|---|---|

Intergroup differences | 2.08291 × 10^{6} | 1 | 2.08291 × 10^{6} | 113.26094 | 3.85 |

Intragroup differences | 2.21971 × 10^{7} | 1027 | 18390.333 | ||

Sum | 2.428 × 10^{7} | 1028 |

_{α}, showing a significant difference between the two sets of data.

Zone | $\mathit{z}/{\dot{\mathit{Q}}}^{2/5}$ [m/kW^{2/5}]
| $\mathit{\kappa}$ | $\mathit{\eta}$ |
---|---|---|---|

Continuous flame zone | <0.08 | 6.8 [m^{1/2}/s] | 1/2 |

Intermittent flame zone | 0.08–0.2 | 1.9 [m/kW^{1/5} s] | 0 |

Plume zone | >0.2 | 1.1 [m^{4/3}/kW^{1/3} s] | −1/3 |

Zone | $\mathit{z}/{\dot{\mathit{Q}}}^{2/5}$ [m/kW^{2/5}]
| $\mathit{\kappa}$ | $\mathit{\eta}$ |
---|---|---|---|

Continuous flame zone | <0.08 | 4.84 [m^{1/2}/s] | 0.5 |

Intermittent flame zone | 0.08–0.2 | 1.46 [m/kW^{1/5} s] | 0.03 |

Plume zone | >0.2 | 1.31 [m^{4/3}/kW^{1/3} s] | −0.04 |

**Table 5.**Attenuation coefficients of dimensionless smoke temperature rise with dimensionless distance from fire source.

Case 1 | Case 2 | Case 3 | Case 4 | Case 5 | |
---|---|---|---|---|---|

$\alpha $(East) | 1.38 | 1.40 | 1.87 | 2.42 | 2.56 |

$\alpha $(West) | 1.55 | 1.57 | 1.91 | 2.82 | 2.95 |

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**MDPI and ACS Style**

Lin, W.; Liu, Q.; Zhang, M.; Cai, B.; Wang, H.; Chen, J.; Zhou, Y.
Numerical Simulation on Smoke Temperature Distribution in a Large Indoor Pedestrian Street Fire. *Fire* **2023**, *6*, 115.
https://doi.org/10.3390/fire6030115

**AMA Style**

Lin W, Liu Q, Zhang M, Cai B, Wang H, Chen J, Zhou Y.
Numerical Simulation on Smoke Temperature Distribution in a Large Indoor Pedestrian Street Fire. *Fire*. 2023; 6(3):115.
https://doi.org/10.3390/fire6030115

**Chicago/Turabian Style**

Lin, Weidong, Qiyu Liu, Meihong Zhang, Bihe Cai, Hui Wang, Jian Chen, and Yang Zhou.
2023. "Numerical Simulation on Smoke Temperature Distribution in a Large Indoor Pedestrian Street Fire" *Fire* 6, no. 3: 115.
https://doi.org/10.3390/fire6030115