EXPERIMENTS WITH RELEASE AND IGNITION OF HYDROGEN GAS IN A 3 M LONG CHANNEL
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Transcript of EXPERIMENTS WITH RELEASE AND IGNITION OF HYDROGEN GAS IN A 3 M LONG CHANNEL
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EXPERIMENTS WITH RELEASE AND IGNITION OF HYDROGEN GAS IN A 3 M LONG CHANNEL
Ole Kr. Sommersel, Dag Bjerketvedt,Knut Vaagsaether and Torstein K. Fanneløp
Telemark University College,
Porsgrunn, Norway
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Outline
• Introduction and objective
• Experimental setup
• Froude scaling
• Experimental dispersion results
• Numerical dispersion simulations with FLACS
• Flame propagation
• Conclusions
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Introduction
D. Bjerketvedt and A. MjaavattenICHS Conference, Pisa, Sept., 2005
• The hazard, when hydrogen is leaking, is strongly linked to the dispersion of hydrogen.
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Objective
D. Bjerketvedt and A. MjaavattenICHS Conference, Pisa, Sept., 2005
• Get a better understanding of the phenomena and to develop tools that can analyse hydrogen dispersions and explosions in buildings, channels and tunnels
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Experimental setup
Hydrogen inlet
Ign#4 Ign#3 Ign#2 Ign#1 0.1 m
0.5 m0.5 m 0.5 m0.5 m0.5 m
3.0 m
Ign#5
P#2P#1 P#3
Side view
0.1 m
Test #20, Q =31.8 l/min, L = 2 m
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Experimental setup
• Hydrogen gas supply– Hydrogen (99.9%) was injected into the channel through a vertical 4
mm ID steel tube. – The release was directed vertically upwards and the flow velocities
ranged from 2.4 m/s to 99.2 m/s
• Ignition– Siemens ZM 20/10 high voltage igniter. – 5 mm from the upper wall– switched on and off in a series of short pulses ten times per second
• Pressure recordings
– Three Kistler 7001 pressure transducers
• High-speed video– Photron Ultima APX-RS high-speed digital video camera. Frame rate
was typical 2000 fps.
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Flow rates and ignition positions
Hydrogen inlet
Ign#4 Ign#3 Ign#2 Ign#1 0.1 m
0.5 m0.5 m 0.5 m0.5 m0.5 m
3.0 m
Ign#5
P#2P#1 P#3
Side view
0.1 m
Test Series #1 #2 #3 #4 #5
Length, L [m] 0.5 1.0 1.5 2.0 2.5
Qmin [dm³/min] 1.8 2.7 4.6 10.3 17.5
Qmax[dm³/min] 75.0 75.0 75.0 75.0 75.0
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Froude scaling and Gravity Currents
• William Froude (1810-1879)
• In fluid dynamics, a gravity current is a flow in a gravitational field driven by a density difference
• The frontal velocity of gravity currents can typically be expressed by the dimensionless Froude number.
• The Froude number is the ratio between momentum and gravity forces acting in a fluid flow
gh
uFr
Ref. 4
uFr2
r1
r2 > r1
Ref. 3
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Froude scaling
• uF is the average frontal velocity
• H is the height of the the channel
• h is the height of the hydrogen-air layer in the channel
• hH is the height of a 100 % hydrogen layer in the channel.
uF
hH hH
whuQ HFH
F
gh
uFr
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Froude scaling
uF
hH hH
gQ
wuFr
3F 3
2
w
gQFrLuF
gQw
LFr
3
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Froude versus volume flow
gQwL
Fr3
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• We have extended the model for "light-fluid intrusion" given by Gröbelbauer et. al. [5] when the Froude number is based on the length scale hH
• Φ = 0.5 and hH << H we get Fr = 0.68
“Light-fluid intrusion" for gravity currents
32
3
gQFr
wL
)1(
)1)(2(
1
1
rrr H
HH
F
hH
H
gh
uFr
uF
hH hH
Φ = h/H
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Time of ignition
32
3
gQFr
wL
Fr = 0.68
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Hydrogen concentration
Fr = 0.68
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FLACS results
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Flame propagation
• Triple flames (rich layer)
– Phillips [8] 1965
– LPF, lean premixed flame
– RPF, rich premixed flame
– DF, diffusion flame
Ref. Chung [9]
uF
hH
Test #20, Q =31.8 l/min, L = 2 m
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Maximum explosion pressures
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Conclusions
• The time of arrival of the gas cloud at the continuous ignition source appear to be well described by Froude scaling with a length scale corresponding to the height of a layer of 100 % hydrogen in the channel
• We believe that this Froude scaling can be useful as a tool to analyse the consequences of hydrogen release in buildings, channels and tunnels
• Further work is needed in order to establish the validity of this scaling for other conditions than those of the present small scale tests