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A Numerical / Analytical Model of Hydrogen Release and Mixing in
Partially Confined Spaces
Kuldeep Prasad, William Pitts and Jiann Yang
Fire Research Division
National Institute of Standards and Technology
Gaithersburg, MD 20899.
NHA 2010 Annual Conference
e-mail : [email protected]
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Fire safety in confined spaces
Hydrogen powered systems– Rising energy demands– Environmental degradation problem
Transition to a hydrogen economy poses new safety challenges
– Unique fire hazard - Hydrogen behaves differently than conventional fuels
– Lack technical data to support standard and code development – partially enclosed compartments.
What is the problem?
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H2 Flammability, Detection, & Fire Safety
To study fire hazards associated with accidental release of
hydrogen in residential and commercial settings and to provide
sound technical data to support hydrogen fire safety code and
standard development.
● Hydrogen fire safety in partially confined spaces
● Release and mixing of hydrogen in confined space.
● Short and long term mixing and dissipatioin.
● Simple theoretical tools, CFD simulations, Experiment
● Hydrogen flammability.
● Standardization of test protocols for hydrogen detection.
● Code and standard activities (NFPA-2)
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Hydrogen Release as a Point Source•Release of hydrogen as a point source.
• Un-cluttered environment
• Turbulent hydrogen plume entrains air.
• Plume reaches ceiling and spreads radially.
• Buoyant layer separated from ambient air by a density interface.
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Problem Formulation
c3
ci1
PP
P)hH(gP
jjj c*v*ajQ
0
c3
0
ci1
P2v
P)hH(g2v
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Conservation Equations
)cva())hH(
333i
22
2
HHH YMdt
SYd
333
i cva))hH(
pQdt
Sd
Conservation of Hydrogen in upper layer
Conservation of total massin upper layer
Constraint Equation
Plume ModelingClassical Plume Mixing Model – self similar plume solution
3/50
3/10
3/12
10
9
5
6zhBQ ip
gVB HH **
0
00
2
2
Buoyancy FluxEffective origin
333111 cvacva2
HV
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Hole
Burner
1.5
m
0.75
m
1.5 m
Sensor 7 (0.65 m)Sensor 6 (0.56 m)Sensor 5 (0.45 m)Sensor 4 (0.37 m)Sensor 3 (0.28 m)Sensor 2 (0.19 m)Sensor 1 (0.09 m)
Reduced scale experiments
Comparison with Analytical Model
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Full Scale CFD simulationsComparison with Analytical model
Hole
Burner
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Effect of Hydrogen Release RateHydrogen Volume Fraction Height of the Interface
Compartment Overpressure Volumetric Flow Rates
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Wind Driven Ventilation of Compartment
Assisting Wind FlowWind assists buoyancy driven flow
Opposing Wind FlowWeak wind opposes buoyancy driven flow
Opposing Wind FlowStrong wind opposes buoyancy driven flow
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Wind Driven Ventilation-Steady State Results
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Forced Venting of Hydrogen: Formulation
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Forced Venting of Hydrogen : Results
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Release as a Distributed Source
• Release of hydrogen under an obstruction.
• Cluttered environment, Multiple plumes.
• Buoyant gas mixes rapidly with surrounding air.
• Well mixed hydrogen air mixture in compartment.
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Problem Formulation
)cva( 33322
2
HHH YM
dt
YdV
Conservation of hydrogen in compartment
Constraint Equation
333111 cvacva2
HV
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Effect of Vent Area, Location
Multiple Vents
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Conclusions and Future Work• Natural and wind driven ventilation of hydrogen
released in an accidental manner in a partially enclosed compartment.
• Development of simple analytical models– Validated with reduced scale experiments.– Validated with full scale detailed CFD simulations.
• Effect of Hydrogen Release Rate• Effect of vent cross-sectional area, distance between
vents, multiple vents, location of vents.• Role of assisting and opposing wind flows• Forced ventilation, thermal effects,• Effect of surrogate gases (helium).• Time to empty a compartment filled with hydrogen gas.