# A Numerical Analysis of the Fire Characteristics after Sprinkler Activation in the Compartment Fire

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Fire Dynamics Simulator and Fire Suppression Model by Water

^{2}) can be expressed in the following equation:

^{2}) when no water droplets are applied, and $k(t)$ is a linear function of the local water mass per unit area, ${{m}^{\u2033}}_{w}(t)$, in units of kg/m

^{2}, which is expressed as:

^{2}/(kg·s). The extinguishing coefficient is dependent on the material properties of the solid fuel and its geometrical configuration. In order to obtain the optimal α value, simulations were performed for calibration by comparison of the ceiling temperature. The detail will be discussed in the next section.

## 3. Experiment Setup

^{0.5}. The operation pressure was 1 bar. The spray angle of 10 to 80 degrees was estimated by image analysis. Two K-type thermocouples (range: −200 to +1000 °C, accuracy is ±1 °C) were installed 76 mm from the ceiling to measure the temperature. The ceiling temperature data were recorded by a portable data logger, a midi LOGGER GL240, every second (the measurement accuracy: 0.05% for the K-type thermocouple).

## 4. Numerical Detail

^{2}. The HRR assigned to the top surface of the wood crib and interior surface of polyether foam (red surface, Figure 2). Sprinkler and ceiling thermocouples were installed in the same location in the experiment. The boundary conditions assigned “OPEN” for the computational domain, and “ADIABATIC” to the wall and floor. The ambient temperature was 29 °C, in agreement with the experiments. A Cartesian coordinate system indicated at the center of the compartment for convenience in the analysis.

^{0.5}) which can be obtained from the manufacturer and $p$ is the pressure of the pipe in Bar.

_{v}

_{,0.5}is the median volumetric droplet diameter, µm (i.e., half the mass is carried by droplets with diameters of D

_{v}

_{,0.5}or less), γ and σ are empirical constants equal to approximately 2.4 and 0.48, respectively [12]. The median droplet diameter, D

_{v}

_{,0.5}, is estimated using the formula reported by Yu [19]:

^{3}, ${u}_{d}$ is the initial droplet velocity in m/s, and ${\sigma}_{d}$ is the water surface tension in N/m. Analysis of Sheppard’s [18] data provided an average value of ${C}_{sp}$ approximately 1.53 for sprinklers test.

## 5. Result and Discussion

#### 5.1. Optimal Extinguishing Coefficient

^{2}/(kg·s) and 4.0 m

^{2}/(kg.s), the ceiling temperature of numerical simulation decreases with an increasing extinguishing coefficient. Comparing ceiling temperature, the value of the extinguishing coefficient α = 3.0 m

^{2}/(kg·s) provides the best fit temperature between numerical and experimental data at both points. These comparisons demonstrate that the fire suppression model in FDS can capture the features of fire characteristics under the effect of sprinkler spray.

#### 5.2. Temperature and Flow Field

#### 5.3. Effect of Sprinkler Spray on Smoke Spread

## 6. Conclusions

- The extinguishing coefficient of 3.0 was chosen for the fire suppression model in this study. Under the effect of sprinkler spray, the HRR stopped growing at 165 kW at 70 s and then reduced rapidly to 10 kW at 400 s;
- The hot upper layer rapidly reduced both the temperature value and the area of the layer during fire suppression. The smoke layer was formed with a symmetrical cone right below the sprinkler, revealing the smoke logging phenomena. Under the influence of sprinkler spray, the combination of smoke logging and fresh air-entraining from the left door pushed the smoke logging to occur strongly in the right region afterwards;
- Heat Release Rate reduction and smoke logging phenomena inside the compartment presented a significant effect of the sprinkler spray on the smoke spread in the doorway. The temperature of the smoke layer through the doorway reduced to an ambient temperature of 200 s after activating the sprinkler. The smoke velocity inside the sprinkler spray could reach over 2 m/s. At the doorway, however, the smoke velocity reduced to 0.5 m/s at 300 s, much lower than the 2 m/s in the free burn case. The mass flow rate through the doorway in the sprinkler case reduced to half compared to the free burn case at 200 s;
- The extinguishing coefficient in this study can be used as a first step trial for other researchers who want to apply the fire suppression model. However, the fire suppression model defined by the calibration method depends not only on the material properties and geometry of solid fuels but also on water spray distribution. Therefore, several important spray characteristics, such as water droplet size, spray angle, and initial velocity, need attention when referring to an extinguishing coefficient. Sensitive to these factors, we will further investigate.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Detailed drawings of the compartment in the experiment: (

**a**) test compartment layout; (

**b**) sprinkler spray; (

**c**) test compartment; and (

**d**) fire source.

**Figure 2.**Independent measurement of heat release rate for (

**a**) the wood crib and (

**b**) polyether foam.

**Figure 3.**Experiment results: (

**a**) heat release rate in the free burn and (

**b**) ceiling temperature in the compartment with sprinkler activation.

**Figure 6.**Variation of ceiling temperature with different extinguishing coefficients: (

**a**) Point 1 and (

**b**) Point 2.

**Figure 8.**Temperature distribution and vector field of the smoke layer in vertical plane y = 0 m: (

**a**) temperature distribution before sprinkler activation, 70 s; (

**b**) velocity field before sprinkler activation, 70 s; (

**c**) temperature distribution after sprinkler activation, 100 s; (

**d**) velocity field after sprinkler activation, 100 s; (

**e**) temperature distribution at 150 s; (

**f**) velocity field at 150 s.

Sprinkler Parameter | Value |
---|---|

Flow rate | 50 L/min |

Velocity | 6.01 m/s |

Droplet size | 954 µm |

Atomization distance | 0.2 m |

Angles | 10–80° |

Activation temperature | 68 °C |

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**MDPI and ACS Style**

Khoat, H.T.; Kim, J.T.; Quoc, T.D.; Kwark, J.H.; Ryou, H.S. A Numerical Analysis of the Fire Characteristics after Sprinkler Activation in the Compartment Fire. *Energies* **2020**, *13*, 3099.
https://doi.org/10.3390/en13123099

**AMA Style**

Khoat HT, Kim JT, Quoc TD, Kwark JH, Ryou HS. A Numerical Analysis of the Fire Characteristics after Sprinkler Activation in the Compartment Fire. *Energies*. 2020; 13(12):3099.
https://doi.org/10.3390/en13123099

**Chicago/Turabian Style**

Khoat, Ho Trong, Ji Tea Kim, Tran Dang Quoc, Ji Hyun Kwark, and Hong Sun Ryou. 2020. "A Numerical Analysis of the Fire Characteristics after Sprinkler Activation in the Compartment Fire" *Energies* 13, no. 12: 3099.
https://doi.org/10.3390/en13123099