Abstract
Natural convection roof vents are widely used in industrial and other buildings for clearing smoke and toxic gases produced by fires and explosions. In the design of such vents where hot gases are driven out by pressure differences, it has been a common practice to ignore the effects of outside wind. Buoyancy is assumed to be the only driving force.
This paper shows that under certain wind conditions the effects of wind can completely override buoyancy, causing either flow reversal or inefficient extraction.
A new design method, based on wind tunnel measurements, is proposed by which the effects of wind can be taken into account. A worked example is presented to illustrate the method.
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Abbreviations
- A :
-
area
- C :
-
flow coefficient
- C p :
-
pressure coefficient
- d b :
-
layer depth
- g :
-
gravitational acceleration
- \(\dot m\) :
-
mass flow rate
- p :
-
pressure at a point
- \(\dot Q\) :
-
volume flow rate
- R L :
-
leakage ratio defined in Equation 7
- T :
-
temperature
- U :
-
velocity of air/gas
- α :
-
wind incidence
- ρ :
-
density
- Δp :
-
pressure difference
- a :
-
ambient
- g :
-
gas
- i :
-
inside
- o :
-
outside
- r :
-
roof, reference height
- T :
-
temperature (buoyancy)
- w :
-
wind
References
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Kandola, B.S. Effects of atmospheric wind on flows through natural convection roof vents. Fire Technol 26, 106–120 (1990). https://doi.org/10.1007/BF01040176
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DOI: https://doi.org/10.1007/BF01040176