1 peter v. nielsen, aalborg university [email protected] smoke ventilation and building design
TRANSCRIPT
2Peter V. Nielsen, Aalborg University
The lectures
- Introduction and the Danish ”Bygningsreglement”
- Design fire
- The development of thermal smoke ventilation and the Thomas plume model
- Plume flow, the Heskestad plume model and other flow elements
- Mechanical smoke ventilation
- CFD models
- Model experiments
- Evacuation models
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Design of Fire Conditions
Design fire
Model for smoke movement
tcritical
Model for evacuation
tevac>
Distribution of people
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Virtual origin
y is negative below floor level
If y is equal to 5 m and yo isequal to -1 m, then (y-yo) is equal to 6 m.
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Flame height
Found from experiments which relate flame heights toFire load and diameter of fire.
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Heskestad, Temperature and Velocity in the Flame
QQc 8.0...6.0
Convective heat emission
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Heskestad, mass flow in plume
My for y > L
My for y < L
Mass flow versus height. Mass flow is dependent on flame height.
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Free Thermal Plume, Wall Plume and Corner Plume
My = f(Q) My = 0.5•f(2Q) My = 0.25•f(4Q)
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Temperature in smoke layer, two methods
1) Simple expression.
2) Advanced expression taking account to heat loss to surroundings:
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Radiation
Radiation is a fixed part of the energy release. Typically 30%, but it is dependent on the material which is burning.
– Petrol 0.18– Polystyrene 0.44
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Flame height and room height
L is free flame height
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Flame height and room height
Tid
Forb
ræn
din
gsh
ast
igh
ed
[g /
s m
²]
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Critical Size of the Smoke Exhaust to Prevent Plug Holing
mcr (kg/s) , g (m/s2), hs (m) , T (K) and (K) are criticalflow, gravity, thickness of smoke layer, temperature of thesurroundings in Kelvin and excess temperature in the smoke,respectively.
= 1.3 close to a wall and 1.8 far from a wall.
N > M/mcr
where N and M (kg/s) are a minimum number of openings, and a flow rate of smoke which has to be exhausted.
17Peter V. Nielsen, Aalborg University
The lectures
- Introduction and the Danish ”Bygningsreglement”
- Design fire
- The development of thermal smoke ventilation and the Thomas plume model
- Plume flow, the Heskestad plume model and other flow elements
- Mechanical smoke ventilation
- CFD models
- Model experiments
- Evacuation models
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Mechanical Smoke Ventilation, 1
The height yst is foundfrom the mass flow Mst
exhausted by the fans.
Based on Thomas’sequation.
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Mechanical Smoke Ventilation, 2The Danish Pavilion in Seville 1992
The Danish Pavilion in Seville was equipped with mechanical smoke ventilation. The exhaust fan had a capacity of 10 m3/sec.
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Building with Hybrid Ventilation and Mechanical Smoke Ventilation
Office building (KTH-south) in Stockholm. Ventilated by hybrid ventilation.
Smoke ventilation is based on mechanical fan exhaust.
21Peter V. Nielsen, Aalborg University
The lectures
- Introduction and the Danish ”Bygningsreglement”
- Design fire
- The development of thermal smoke ventilation and Thomas plume model
- Plume flow, Heskestad plume model and other flow elements
- Mechanical smoke ventilation
- CFD models
- Model experiments
- Evacuation models
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Computer Simulation of Smoke Movement
• Increased accuracy of the predictions• Complex geometry• Small fire load and small buoyancy effect on the smoke• Consideration of other air flows and pressure
distribution in the building• Outside the area of validation of simplified models• Visualization of the predictions• Problems and connections between smoke ventilation
and other functions in the building can be addressed
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Fire in a Theatre
Dimensioning of smoke ventilation in a theatre byFLOVENT and FDS
The stage room has a height of 31 m and a floor area of 20 x 20 m
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Flovent 4.1
Based on averaged equationsand the k-epsilon model
Direct output is:
Height to smoke layer
Temperature distribution
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FDS 3.1
Based on the fundamental equations and largeeddy simulation
Direct output is:
- Height to smoke layer- Temperature distribution- Radiation from smoke layer- Visibility in the occupied zone
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Fire in a Tunnel
The Ofenegg experiments were made in a 131 m long deadend tunnel in Switzerland.
Smoke development in the openingone minute after ignition of 500 lkerosine.
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Smoke movement in a tunnel
Measured and predicted velocity profile. The predictionsare based on a zero equation model and on a k-epsilonModel. Fr = 0.34.
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Smoke movement in a tunnel
A Low Reynolds Number model improves thepredictions in the small scale situation, butis the smoke movement also semi-laminarin full scale flow?
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Dynamic Simulation of Smoke Movement in the Ofenegg Tunnel
The position of smoke after 20, 59 and 114 sec.The speed of the smoke front is 2 m/s shortly after ignition of the fire.
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Computer Simulation, Stansted Airport
Airport terminal. Theheight is 13 m and thefloor area is 32000 m2.
Computer animation ofsmoke movement andevacuation.
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Computer Simulation, Munich Airport
Railway station at Munichairport.
Simulation of evacuationtime and temperature inthe ceiling structure(stability of the steel struc-ture).
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Computer Simulation, Eurotunnel
Design of effective fire detection and fire-fighting system.
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Computer Simulation, Tunnel ventilation
Fire in a train. Optimization of ventilation in tunnel.
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Computer Simulation, Millennium Dome
Simulation of indoor climate andsmoke ventilation. Real timeprediction of smoke movementduring 30 minutes.
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Smoke Movement in an Artium with low Heat Release
The fire is of 15 kW corresponding to the fire in a dustbin. The cold surfaces are 15C, and the warm surfaces are 25C.The initial temperature in the atrium is 23C. The figures show the situation after 100 seconds of fire.
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Smoke Movement in an Atrium with Open Storeys (Low Heat Release)
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The lectures
- Introduction and the Danish ”Bygningsreglement”
- Design fire
- The development of thermal smoke ventilation and Thomas plume model
- Plume flow, Heskestad plume model and other flow elements
- Mechanical smoke ventilation
- CFD models
- Model experiments
- Evacuation models
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Stratification Height in the Room
Model experiment ona scale of 1 : 15
Height to smoke layer yst versus the Archimedes number Ar
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Fire in a Tunnel, 1
The Ofenegg experiments were made in a 131 m long deadend tunnel in Switzerland.
Smoke development in the openingone minute after ignition of 500 lkerosine.
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Fire in a Tunnel, 2
Smoke developmentof three differentfires of 100 l, 500 land 1000 l kerosine.
All the experimentsshown were madewith natural ventila-tion from the tunnelopening.
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Design of Heat Source
The design makes it possible to work with large Reynolds numbers, or a small scale compared to the full simulation of the heat source.
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Model Experiments, 1
Model of a tunnelon a scale of 1 : 20.
Stratified two-zoneflow in the model.
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Double Facade
The double facade is open at the top and at the bottom, and it is without any restrictions or divisions.
The important parameters of this problem are the temperature distribution and smoke movement in the double facade
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Design of a Fire Source
Fire source
Flow in an office room
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Model Experiments with Double Facade
Model experiments with smoke movement in a double facade. Surface distance is 0.3 m.
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Plume in temperature gradient
Stratification height is equal to
ym = 0.98·Φk1/4(dT/dy)-3/8 + y0
yst1 = 0.55·ym
yst2 = 0.77·ym
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Plume in Temperature
Gradient
ym = 0.75·Φk0.25(dT/dy)-0.26
yst1 = 0.23·Φk0.23(dT/dy)-0.06
yst2 = 0.44·Φk0.21(dT/dy)-0.04
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Trench Effect
The trench effect was seen to cause hot gases in the buoyant plume to lay along the escalator surface and create a rapid airflow which caused these gases to curl over towards the next steps above. The airflows in the trench increased in proportion to the size of the fire, eventually creating a flamethrower type effect up and into the ticketing hall.
53Peter V. Nielsen, Aalborg University
The lectures
- Introduction and the Danish ”Bygningsreglement”
- Design fire
- The development of thermal smoke ventilation and Thomas plume model
- Plume flow, Heskestad plume model and other flow elements
- Mecahanical smoke ventilation
- CFD models
- Model experiments
- Evacuation models
54Peter V. Nielsen, Aalborg University
Design of Fire Conditions
Design fire
Model for smoke movement
tcritical
Model for evacuation
tevac>
Distribution of people
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Evacuation Simulation
• Hand calculation
• Simulex
• BuildingEXODUS
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Hand Calculation
Walking velocity when people can move uninfluenced of eachother.This is the case if the density of people is smaller than 1.0 persons/m2 and if people has a normal mobility.Valid for category 1 – 5.
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Relationship between Flow Rate and Crowd Density
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Hand Calculation
Not the whole width of stairs are used for movement. The width must be reduced with 0.3 m in the calculation of walking time.
The capacity is valid for stairs with an angle of 26o – 32o inrelation to a horizontal surface. Larger angles should be avoided
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Peak Flow Rate through Passageways
International Maritime Organisation set ‘maximum’ flow rate through passageways to 1.33 persons/m/s
Denmark: 1 person/m width/sec
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Hvad siger virkeligheden?
• Det er sjældent at flugtvejens kapacitet har været kritisk
• Varsling, reaktion og beslutning tager meget længere tid end selve rømningen
• ”Katastrofebrande” er ofte forbundet med et meget hurtigt og volsomt brandforløb
• Den største del af personerne vælger at flygte gennem den samme vej som de kom ind i bygningen gennem
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Simulex Evacuation Model
Simulation of 350 people leaving a discotheque in GoteborgIn case of fire
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Validation of Evacuations Models
In general, the programs are able to Predict movement of people with reasonable accuracy.
