Study of Hydrogen Diffusion and
Deflagration in a Closed System
Yuki Ishimoto1, Erik Merilo2, Mark Groethe2, Seiki Chiba3,
Hiroyuki Iwabuchi1, Ko Sakata1
1The
Institute of Applied Energy, Japan
2SRI International, USA
3SRI International, Japan
Poulter Laboratory
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Outline
1. Introduction
- Our early studies, motivation and objective
2. Experimental facility
- Facility
- Measurement
3. Experimental Procedure
4. Results
5. Summary
Studies were administered through NEDO as part of the
“Establishment of Codes & Standards for Hydrogen
Economy Society”.
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1.Introduction
Our early study and motivation;
- A variety of R & D projects including stationary fuel cells, fuel cell
vehicles and hydrogen supply infrastructure are being conducted in
Japan.
- As a part of this activity, deflagration studies of pre-mixed gas and
hydrogen releases in open systems and partially confined systems
have been performed.
- However hydrogen concentrations tend to be higher in closed
systems under the same release condition.
37m3
Tunnel 76m long
300m3
Facilities for hydrogen deflagration research
2nd ICHS 11-13/9/2007 Spain
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Objectives
- Overpressures caused by the deflagration of hydrogen-air mixtures
in closed systems can be larger than that in open systems due to
the confinement.
- In closed systems, mechanical ventilation should be used to
decrease the hydrogen concentration to levels below the lower
flammability limit (LFL).
- In order to reduce the risk associated with hydrogen use in
confined spaces it is necessary to study how the ventilation rate
and release rate effect the hydrogen concentration in a closed
system.
- This work is intended to aid in the estimation of an appropriate
ventilation rate for a confined space in which hydrogen is stored or
used.
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2. Experimental facility
Experiments were conducted at the SRI International experimental test site
The facility:
- Constructed out of welded steel,
- Designed to be able to withstand an internal detonation.
Dimensions
- Height: 2.72 m
- Width: 3.64 m
- Length: 6.10 m
- Volume: ~60 m3
1.22m
0.09m
- The open end was covered with a
sheet of 0.0076 mm high density
polyethylene (HDPE) for the tests.
- This allowed visible and infrared
cameras to capture images of the
flame.
- A ventilation intake hole was cut at
the bottom of the plastic sheet.
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Inside of the facility
- The release nozzle was installed at the center of the floor.
- The hydrogen gas was released toward the ceiling.
- Overpressures from the hydrogen deflagration were measured with
four pressure transducers mounted flush on the walls of the facility.
- A constant hydrogen release rate
was obtained by using a regulator
to control the pressure upstream
of a critical flow venturi.
- The hydrogen release rate was
measured using a thermal mass
flowmeter.
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Measurements
Thermocouple
Spark ignition
module
Sample
stations
Release nozzle
Sample stations
Thermocouple
Sample
stations
Thermocouples
- Gas sampling system: 9 locations
- Fast-response coaxial thermocouples :
Spark ignition
module
Thermocouples
to measure the time-of-arrival (TOA) of
flame front.
- Electronic spark ignition modules: on
the ceiling and next to the release jet.
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Gas sampling system
Pressure
readout
Pressure sensor
Sampling
H2 sensor
Valve
Sample
H2 & air
Hydrogen
readout
Evacuated
Manifold
Valve
Vacuum
pump
Sampling Setup
Measurement Analysis Setup
- The bottle was evacuated before the
experiment.
- The mixture was sampled when valve
was 3 was opened
- 3 bottles make up one sampling system.
- After the experiment the bottle was
attached to the setup to be analyzed.
- The absolute pressure and hydrogen
partial pressure were recorded.
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Ventilation
- Ventilation rates were measured using a hot wire anemometer.
- A 10-second average flow velocity was measured at seven points
before testing to obtain the velocity profile.
- During the experiment an anemometer was placed on the center line of
the duct and the velocity was recorded.
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3. Experimental Procedure
Time sequence of a test
0 sec
800 sec
1600 sec
2400 sec
Ventilation
Hydrogen release
Gas sampling: 3 sec
Spark Activated: 5 sec,
Interval : 5 sec (on the ceiling)
1 sec (next to the nozzle).
- Prior to the test the ventilation rate was measured.
- The hydrogen was released at a constant rate.
- The hydrogen and air mixture near the ceiling was sampled at 3 times and 9
different locations.
- The spark ignition modules installed on the ceiling were activated for 5
seconds just after the third gas sampling. (This procedure of timing the
spark ignition modules ensures that there is only a single ignition point.)
- The hydrogen gas release was stopped after the last spark ignition module
was turned off.
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4. Results
Parameter combination of release experiments
Test 23
Test 19
Test 26
Test 22
Test 18
Test 25
Test 21
Test 17
Test 24
0.4
3
Ventilation speed (m /s)
0.5
0.3
0.2
Test 16
Test 20
0.1
0
0
0.005
0.01
0.015
0.02
Hydrogen release rate (m 3/s)
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Time (seconds)
Ventilation rate (Nm3/s)
Release rate (Nm3/s)
Release rate and Ventilation
Time (seconds)
The hydrogen release rate and ventilation rate were nearly
constant for each experiment.
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Maximum hydrogen concentration (%)
Hydrogen density
4
3.5
3
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
60
Time (min.)
- The hydrogen concentration reached about 1.5% at 4 minutes.
- The hydrogen concentration seems to increase very slightly until 30 min.
- Based on this result, a release duration of 40 minutes was selected for the rest
of the tests.
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Impulse (kPa-s)
Overpressure (kPa)
Overpressure and impulse
0.02m3/s
Time (seconds)
- Hydrogen release rate:
- Ventilation rate: 0.1m3/s.
- Hydrogen concentration before ignition: 15~17%.
- The hydrogen-air mixture was ignited by the spark ignition module located on the ceiling.
- A pressure pulse was generated when the hydrogen-air mixture ignited on the ceiling.
- The highest overpressure and impulse were 0.77 kPa and the 110 Pa-sec, respectively.
- The measured overpressures were very low and represented a small risk to people and
property.
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Range (m)
Flame front velocity
Time (seconds)
The flame speed estimated from the TOA data was the highest of all
tests and accelerated from 9.3 m/s to 13.7 m/s in this test.
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Hydrogen concentration
- The maximum concentration is
proportional to the ratio of the
hydrogen release rate and the
ventilation rate within the range of
parameters tested in the present study.
- Therefore a required ventilation rate can
be estimated from the assumed
hydrogen leak rate within the present
experimental conditions.
- Further experiments in closed systems
are necessary, varying additional
parameters (volume, the direction of
the nozzle…).
Maximum hyrdgen concentration (%)
20
15
10
5
0
0
0.05
0.1
0.15
0.2
The ratio of hydrogen release rate to
ventilation speed
The correlation between the ratio of the hydrogen
release rate to ventilation rate and the maximum
hydrogen concentration.
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5. Summary
- Experiments were performed to study how the ventilation rate
and the release rate effect the hydrogen concentration in a
closed system.
- Various combinations of hydrogen release rates and ventilation
rates were explored in a test facility (Volume: 60m3).
- The hydrogen release rate ranged from 0.002 m3/s to 0.02 m3/s.
The ventilation rate varied from 0.1 m3/s to 0.4 m3/s.
- Overpressures measured in tests were very low and
represented a small risk to people and property.
- The maximum concentration inside the facility was
proportional to the ratio of the hydrogen release rate and the
ventilation rate within the range of parameters tested.
- Therefore a required ventilation rate can be estimated from the
assumed hydrogen leak rate within the experimental
conditions used in this study.
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Acknowledgement
- Authors would like to thank NEDO for their
financial support and fruitful comments.
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Thank you for your kind attention !
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Ventilation
- The flow velocity profile in the ventilation duct was measured by placing an anemometer
at different heights and taking the 10-second average at a given location.
Measurements were taken at heights of 1 cm, 5.6 cm, 11.2 cm, 16.8 cm, 22.4 cm, 28.0 cm,
and 32.7 cm inside the duct.
- The velocities measured at these locations were then averaged in proportion to the
circular area represented by the measurement point in order to obtain the average bulk
flow velocity.
- The anemometer was then placed at the centerline of the ventilation tube, and data were
recorded for at least 10 minutes prior to the test. This centerline velocity was then
averaged.
- The average centerline velocity was then multiplied by the percentage of the bulk
average velocity from the profile data.
- This gave an average bulk flow velocity that was multiplied by the duct’s area to obtain
an average volumetric flow rate for the ventilation of the facility.
a schematic of the measurement locations
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Cross-sectional schematic of the facility
Gas sampling
Spark module
2
1
3
Outlet
2.72m
Open end: film
H2
Pressure
transducer
Inlet
6.1m
Nozzle
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