accumulation of hydrogen released into a vented … · – wind driven ventilation model (quadvent)...
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An Agency of the Health and Safety Executive
www.hsl.gov.ukAn Agency of the Health and Safety Executive
Accumulation of Hydrogen Released into a Vented Enclosure – Experimental Results
P. Hooker, J. Hall, D. Willoughby, J. Hoyes
© British Crown copyright 2013. This publication and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.
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Contents• Objectives• Experimental arrangement• Initial experimental results• Comparison of results with some simple
models• Follow-on work
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Objectives• Part of the EU Hyindoor Project
– Address knowledge gaps for hazards of hydrogen in confined spaces (e.g. enclosures, containers, warehouses etc)
– See Paper ID 128 for more details of overall project– http://www.hyindoor.eu/
• Work Package 2 (WP2)– dispersion and accumulation of hydrogen
• WP2 HSL experiments– study dispersion and accumulation
• At large scale (31m3 enclosure)• Subject to real wind conditions (enclosure sited outdoors)• Using a range of passive vent arrangements
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Experimental Arrangement
H2
Flow controller: 0 – 200 Nl/min
Enclosure(31m3)
P
AccessPorch
Remotely actuated valve
PEmergency explosion blast panels fitted in roof
Pipe exit
N2
Manually actuated valve
Flow check valve
Flow controller: 200 – 1000 Nl/min
Pressure transducers: 0 – 25 barg
Regulators attached to supplies
Nylon tubing
Stainless pipe
Flexible hoseN2 supply
H2 supply 175 bar max. from cylinder pack
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Circular roof vent, same area as rectangular vents, diameter 0.535m
0.27 m high
~ 0.1 m above inner floor of enclosure
VENT 1
VENT 5
VENT 3
~ 0.1 m from end 0.83m
~ 0.1 m below inner ceiling of enclosure
5 m
Enclosure 2.5 m high, 2.5 m wide and 5m long
VENT 4
VENT 2
VENT 6
Experimental Arrangement
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Experimental Arrangement
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Experimental Arrangement
• 27 electrochemical celloxygen sensors
• Mounted on suspendingwires
• In “layers” at 1 m, 1.75 mand 2.25 m from floor
• Additional oxygen sensorsplaced within the openvents as required
• Hydrogen concentration calculated from oxygen depletion detected by each sensor.
Instrumentation :
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Experimental Arrangement
• 14 thermocouples (Type K)• Mounted on suspending
wires• Additional thermocouples
peened into the centre of each of the 6 walls of the enclosure (i.e. the four walls, the ceiling and the floor)
• Additional thermocouple placed within each open vent as required.
Instrumentation :
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Experimental Arrangement
• Pressure transmitters were installed on the hydrogen supply pipeline.
• Bidirectional probes connected to differential pressure transmitters (+/- 19.6 Pa)were installed for some of the later runs in an attempt to detect flow through theopen vents.
• Weather conditions close to the enclosure were monitored (i.e. wind speed, winddirection, temperature and humidity).
Instrumentation :
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Experimental Arrangement
• Experiments with single vent – Upper vent in side wall
• Wind incident on vent / Wind on opposite side to vent
– Roof vent
• Experiments with more than one upper vent– On opposite sides
• Experiments with one lower vent and one upper vent– On opposite sides
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Initial results
• Experiments with single upper vent with wind “not incident on vent” :
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Initial results
• Experiments with single upper vent with wind “not incident on vent” :
Wind temporarily changes direction and blows into open vent
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Initial results
• Experiment with single upper vent with wind incident on vent :
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Initial results
• Experiment with single upper vent with wind incident on vent :
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Initial results • Experiments with single vent – side vent versus
roof vent:
Flow rate : 150 Nl/min;Vent area : 0.224 m 2
Hydrogen flow stopped
Profiles start off similar, then diverge
Some evidence of wind change possibly accounts for some of this
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Initial results • Experiments with multiple vents at high level
(vents at opposite sides of the enclosure):
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Initial results • Experiments with multiple vents at high level
(vents at opposite sides of the enclosure):– Concentrations far lower than predicted by buoyancy-based model
(i.e. Linden)– Wind driven ventilation model (Quadvent) generally gives better
agreement (providing there is wind into vent !)
Hydrogen flow rate (Nl/min)
Average wind speed (m/s)
Actual Volume average H2
concentration (% v/v)
Linden Volume average H2
concentration (% v/v)
Quadvent Volume average H2
concentration (% v/v)
300 3.1 2.2 9.3 100*
150 2.4 0.7 5.9 1.1
300 2.5 1.6 9.3 2.0
600 2.5 2.4 14.8 3.7
* Model not applicable; wind parallel to vent – trea ted as equal pressures on each side => no flow into enclosure
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Initial results • Experiments with one upper side vent and one
lower side vent (vents at opposite sides of the enclosure ; wind into upper vent):
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Initial results • Experiments with one upper side vent and one
lower side vent (vents at opposite sides of the enclosure ; wind into upper vent):
Hydrogen flow rate (Nl/min)
Average wind speed (m/s)
Actual H2 concentration
Average / Maximum(% v/v)
Linden Volume H2 concentration in
layer(% v/v)
Quadvent Volume average H2
concentration (% v/v)
800 3.3 3.2 / 4.8 10.6 4.0
1000 3.3 4.1 / 6.5 12.3 4.9
1200 3.3 4.9 / 7.9 13.9 5.9
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Initial results • Interesting
influence of wind ?
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Initial results • Interesting
influence of wind ?
Flow “flips” when velocity ~ 3m/s
Angle ~19º
Vector into vent ~ 1m/s
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Conclusions (so far…..)• For single vents “free” of wind effects,
buoyancy model seems to broadly agree with experimental findings
• For multiple vents with wind effects concentrations appear to be more in line with wind-driven model and lower than buoyancy only model
• Wind into upper vents can overcome buoyancy and reverse the flow in two-vent systems
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Further Work• Further experiments to compare choked
and sub-sonic releases – Completed
• Further experiments measuring concentrations below the 1 m level– Complete
• Further analysis of data from all tests– ongoing
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Acknowledgements• EU JU • HSE• All Hyindoor partners
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References• Ivings, M. J., Clarke, S., Gant, S. E., Fletcher, B.,
Heather, A., Pocock, D. J., et al. (2008). Area classification for secondary releases from low pressure natural gas systems, HSE Research Report RR630. HSE Books, www.hse.gov.uk/research/rrpdf/rr630.pdf.
• Linden, P.F., Lane-Serff, G.F. and Smeed, D.A. (1990). Emptying filling boxes: the fluid mechanics of natural ventilation. J. Fluid Mech., 212, 309-335.
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