e in the space drops after the fire source disappears. Figure 4(c) shows the temperature contours when 600 seconds pass after a fire occurs. The temperature in the space is about 30˚C, which is close to the outdoor temperature of 20˚C.

Figure 5 shows temperature contours on center plane with time for Case 5 where the opening height is 0.5 m, and the smoke exhaust fan operates when a fire occurs. Figure 5(a) shows the result similar to Figure 4(a), which is the result of Case 1. This is because Case 1 and Case 5 have the same analysis conditions at 200 seconds. The analysis result of Figure 5(b) is also similar to that of Figure 4(b), when Case 1 and Case 5 have the same analysis conditions. Mean

Figure 13. Smoke density variations with height of opening for fan-on condition.

Figure 14. CO density variations with height of opening for fan-off condition.

while, as the smoke exhaust fan starts operating from 420 seconds, and the air in the space is completely discharged, the temperature in the space drops to 20˚C, which is the outdoor temperature as in Figure 5(c).

Figure 6 shows temperature variations over time with height of opening for fan-off condition at the “monitoring point” of 1 m in the lower part of Figure 1. As shown in the figure, the temperature of the monitoring point rises to more than 200˚C up to 300 seconds when the fire source is present, and then decreases gradually after the temperature rapidly drops to less than 50˚C up to about 400 seconds after 300 seconds when the fire source disappears. It can be found that as the height of the opening increases, the temperature at the monitoring point becomes lower, and the temperature in the space is almost close to the outdoor temperature of 20˚C at 600 seconds at the opening height ranging from 1.5 to 2.0 m.

Figure 15. CO density variations with height of opening for fan-on condition.

Figure 7 shows temperature variations over time with height of opening at the monitoring point of 1m in the lower part for condition where the smoke exhaust fan operates from 420 seconds after 300 seconds when the fire source disappears. The temperature within the space tends to be similar to that of Figure 6 until 420 seconds but drops close to the outdoor temperature of 20˚C in all opening height conditions due to the action of the smoke exhaust fan after 450 seconds.

Figure 8 shows smoke density contours on center plane with time for Case 1 where the height of the opening is 0.5 m, and the smoke exhaust fan does not operate when a fire breaks out. Figure 8(a) shows the smoke density contours in 200 seconds after the fire, which is a stage where the fire grows, when the smoke density at the top is about 4.0 × 10-4 kg/m3. Figure 8(b) shows the smoke density contours in 100 seconds after the fire disappears when 300 seconds pass. The temperature showed a significant drop at 400 seconds, rather than at 300 seconds when the fire was almost extinguished, but the value of smoke density remains high in the entire upper space even at 400 seconds. And as in Figure 8(c), which shows the smoke density contours in 600 seconds after the fire, the smoke density in the space still shows a high value in 300 seconds after the fire is extinguished. This finding suggests that the smoke generated from the fire cannot be discharged to the outside after the passage of time in the condition where the height of the opening is 0.5 m.

Figure 9 shows smoke density contours on center plane at 600 seconds after the fire for fan-off condition where the height of the opening changes from 1.0 to 2.0 m. Figure 9(a) shows the smoke density contours in the case where the opening height is 1.0 m. Figure 9(b) shows the result obtained from the case where the opening height is 1.5 m, and Figure 9(c) shows the result from the case where the opening height is 2.0 m. As shown in the figure, the smoke density contours is considerably high in the case where the opening height is 1.0 m. However, as the height of the opening increases from 1.5 m to 2.0 m, the amount of smoke discharged to the outside increases, and the smoke density within the space drops sharply. These results show that if the height of the opening increases, the amount of smoke discharged to the outside increases, and the smoke density in the space decreases.

Figure 10 shows smoke density contours on center plane with time for Case 5 where the opening height is 0.5 m when the smoke exhaust fan operates from 420 seconds after the fire source disappears at 300 seconds. Figure 10(a) shows the smoke density contours at 500 seconds after the fire occurs. As shown in the figure, as the smoke exhaust fan operates, a considerable amount of smoke is discharged toward the smoke exhaust fan, and the smoke density within the space becomes lower. Figure 10(b) shows the smoke density contours at 600 seconds after the fire occurs. It can be seen that all of the generated smoke is discharged, and the smoke density within the space is almost zero. These results are in contrast to the results of analysis on the conditions of the same opening height without operation of the smoke exhaust fan and show that the smoke is being discharged well by the smoke exhaust fan.

Figure 11 shows CO density contours on center plane at 600 seconds after the fire occurs in the condition where the height of the opening is 0.5 m. Figure 11(a) shows the CO density contours for the condition where the smoke exhaust fan does not operate, and the smoke density within the space still shows a high value even at 300 seconds after the fire is extinguished. Figure 11(b) shows the analysis results for fan operating condition, and the generated CO is completely discharged, and the CO density within the space is almost zero.

Figure 12 shows smoke density variations over time with the height of opening at the monitoring point of 1 m in the lower part for fan-off condition. As shown in the figure, the smoke density at the monitoring point continues to rise up to 300 seconds when the fire source is present. After 300 seconds when the fire source disappears, the smoke density at the monitoring point does not drop significantly under the condition where the height of the opening is less than 1.0 m, which suggests that the smoke is not discharged properly. On the other hand, the smoke is smoothly discharged to the opening, and the smoke density at the monitoring point is greatly reduced under the condition where the opening height is more than 1.5 m.

Figure 13 shows smoke density variations over time with height of opening at the monitoring point of 1 m in the lower part when the smoke exhaust fan operates from 420 seconds after the fire source disappears at 300 seconds. The smoke density tends to be almost similar to that of Figure 12 until 420 seconds but drops close to zero as the smoke density within the space decreases rapidly in all opening conditions as the smoke is discharged to the outside due to the action of the smoke exhaust fan after 450 seconds.

Figure 14 and Figure 15 show CO density variations over time with the height of opening at the monitoring point of 1 m in the lower part for fan-off and fan-on conditions, respectively. The analysis model suggests that the production rate of CO is smaller than the smoke generation rate, and thus the density value of CO within the space is lower than the density value of the smoke. As shown in the figure, the smoke density at the monitoring point is greatly reduced as CO is smoothly discharged when the smoke exhaust fan operates as in the case of the smoke density.

4. Conclusions

In this study, the numerical model of the portable smoke exhaust fan was derived from the building in which a fire occurred, and the analysis on the smoke and toxic gas exhaust effects was performed. Based on the results, the following conclusions were made.

1) The temperature at the monitoring point rises to more than 200˚C up to 300 seconds when the fire source is present, and then decreases gradually after the temperature rapidly drops to less than 50˚C up to 400 seconds after 300 seconds when the fire source disappears in a situation where the smoke exhaust fan does not operate.

2) The temperature within the space drops close to the outdoor temperature of 20˚C in all opening height conditions due to the action of the smoke exhaust fan after 450 seconds in a situation where the smoke exhaust fan operates in 420 seconds after the fire source disappears at 300 seconds.

3) The smoke density within the space still shows a high value even in 300 seconds after the fire is extinguished under a condition where the height of the opening is 0.5 m, and the smoke exhaust fan does not operate after a fire breaks out.

4) Under a condition where the height of the opening is less than 1.0 m after 300 seconds when the fire source disappears in a situation where the smoke exhaust fan does not operate, the smoke is not discharged properly, and thus the smoke density at the monitoring point does not drop significantly.

5) Meanwhile, even when the smoke exhaust fan does not operate, the smoke is smoothly discharged to the opening, and the smoke density at the monitoring point is greatly reduced under a condition where the opening height is more than 1.5 m.

6) The smoke density drops close to zero as the smoke density within the space decreases rapidly in all opening height conditions as the smoke is discharged to the outside due to the action of the smoke exhaust fan after 450 seconds in a situation where the smoke exhaust fan operates from 420 seconds after the fire source disappears at 300 seconds.

Acknowledgements

This study was carried out with the support of the project, titled “Development of portable and rechargeable smoke exhaust fan for firefighting purpose (10058036)” managed by the Korea Evaluation Institute of Industrial Technology as a part of the industrial technology innovation program of the Ministry of Trade, Industry and Energy. We would thus like to extend our sincere appreciation to the said institutions.

Cite this paper

Kim, J.-Y. (2017) Study of Numerical Analysis on Smoke Exhaust Performance of Portable Smoke Exhaust Fan. Open Journal of Fluid Dynamics, 7, 205-218. https://doi.org/10.4236/ojfd.2017.72014

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