Abstract
Mechanical smoke exhaust systems are usually required in large atria in the Far East. Systems are designed based on empirical expressions in the literature. Most of those design equations were derived from a two-layer zone modelling approach under some geometrical restrictions. Full-scale burning tests on mechanical smoke exhaust system were carried out. From these experiments, it was found that there are significant differences between the measured results in some of the tests and those calculated from the design equations using a two-layer approach. Mass exchange through the smoke layer and cool air layer was identified earlier to be a key point under some conditions. But heat lost through the solid boundaries is another factor as pointed out recently. This point will be further discussed in this paper. A simple model based on a two-layer approach reported earlier will be applied to justify those design equations and experimental results. © Springer 2015. Selection and peer-review under responsibility of the Asia-Oceania Association for Fire Science and Technology.
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Abbreviations
- A :
-
Plane area of fire room (m2)
- A w :
-
Area of convective heat exchange between the smoke layer and the walls and ceiling of the fire compartment (m2)
- C p :
-
Specific heat of air under constant pressure (kJkg−1K−1)
- H :
-
Height of the fire compartment (m)
- h w :
-
Convective heat transfer coefficient between the smoke layer and the walls and ceiling (kWm−2K−1)
- \( {\overset{.}{m}}_c \) :
-
Mass entrainment rate of air at the layer interface (kgs−1)
- \( {\overset{.}{m}}_e \) :
-
Mass flow rate of smoke extraction (kgs−1)
- \( {\overset{.}{m}}_i \) :
-
Mass flow rate of intake air through floor air inlet due to exhaust (kgs−1)
- \( {\overset{.}{m}}_p \) :
-
Mass flow rate of plume at the smoke layer interface (kgs−1)
- m s :
-
Mass of the smoke layer (kg)
- \( \overset{.}{Q} \) :
-
Heat release rate of fire (kW)
- \( {\overset{.}{Q}}_c \) :
-
Convective portion of heat release rate of the fire (kW)
- \( {\overset{.}{Q}}_{\mathrm{loss}} \) :
-
Heat lost of smoke layer (kW)
- t :
-
Time (s)
- T a , T s :
-
Temperature of ambient and smoke (K)
- T st , ΔT st :
-
Average absolute temperature and temperature rise of smoke layer at quasi-steady vented stage (K)
- \( {\overset{.}{V}}_e \) :
-
Volumetric flow rate of smoke extraction (m3s−1)
- z :
-
Height from top of fuel to smoke layer interface, clear height (m)
- Z st :
-
Clear height at quasi-steady vented stage (m)
- ρ α , ρ s :
-
Density of ambient air and smoke (kgm−3)
- ρ st :
-
Density of smoke at quasi-steady state (kgm−3)
- χ :
-
Total heat loss factor from the smoke layer to the fire compartment boundaries
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Acknowledgement
The work is supported by the National Nature Foundation of China under Grant No. 51406241. All authors are members of the PolyU/USTC Joint Research Laboratory on ‘Fire Safety and Technology Research Centre for Large Space’.
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Yi, L., Sun, D., Li, Y., Huo, R., Chow, WK., Fong, NK. (2017). Discussion on Heat Lost Through Solid Boundaries in Modelling Atrium Fires Under Mechanical Exhaust. In: Harada, K., Matsuyama, K., Himoto, K., Nakamura, Y., Wakatsuki, K. (eds) Fire Science and Technology 2015. Springer, Singapore. https://doi.org/10.1007/978-981-10-0376-9_10
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DOI: https://doi.org/10.1007/978-981-10-0376-9_10
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