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2nd ICHS 11-13/9/2007 Spain 1Copyright; 2007 IAE. All rights reserved.
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, Japan2SRI International, USA3SRI International, Japan
Yuki Ishimoto1, Erik Merilo2, Mark Groethe2, Seiki Chiba3, Hiroyuki Iwabuchi1, Ko Sakata1
1The Institute of Applied Energy, Japan2SRI International, USA3SRI International, Japan
Poulter Laboratory
2nd ICHS 11-13/9/2007 Spain 2Copyright; 2007 IAE. All rights reserved.
OutlineOutline
1. Introduction- Our early studies, motivation and objective
2. Experimental facility- Facility- Measurement
3. Experimental Procedure4. Results5. Summary
Studies were administered through NEDO as part of the “Establishment of Codes & Standards for Hydrogen Economy Society”.
2nd ICHS 11-13/9/2007 Spain 3Copyright; 2007 IAE. All rights reserved.
1.Introduction1.Introduction
- 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 300m3 Tunnel 76m long
Facilities for hydrogen deflagration research
Our early study and motivation;
2nd ICHS 11-13/9/2007 Spain 4Copyright; 2007 IAE. All rights reserved.
ObjectivesObjectives
- 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.
2nd ICHS 11-13/9/2007 Spain 5Copyright; 2007 IAE. All rights reserved.
2. Experimental facility2. Experimental facility
Dimensions - Height: 2.72 m - Width: 3.64 m - Length: 6.10 m - Volume: ~60 m3
The facility: - Constructed out of welded steel, - Designed to be able to withstand an internal detonation.
- 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.
1.22m
0.09m
Experiments were conducted at the SRI International experimental test site
2nd ICHS 11-13/9/2007 Spain 6Copyright; 2007 IAE. All rights reserved.
Inside of the facilityInside 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.
2nd ICHS 11-13/9/2007 Spain 7Copyright; 2007 IAE. All rights reserved.
MeasurementsMeasurements
- Gas sampling system: 9 locations
- Fast-response coaxial thermocouples :
to measure the time-of-arrival (TOA) of flame front.
- Electronic spark ignition modules: on the ceiling and next to the release jet.
Sample stations
Sample stations
Sample stations
Thermocouples
Thermocouples
Spark ignition module
Thermocouple
Spark ignition module
Release nozzle
Thermocouple
2nd ICHS 11-13/9/2007 Spain 8Copyright; 2007 IAE. All rights reserved.
Gas sampling systemGas sampling system
Sample H2 & air
Hydrogen readout
Pressure readout
Vacuumpump
H2 sensor
Pressure sensor
Valve
Valve
Manifold
Sample H2 & air
Hydrogen readout
Pressure readout
Vacuumpump
H2 sensor
Pressure sensor
Valve
Valve
Manifold
Sampling Setup Measurement Analysis Setup
Evacuated
Sampling
- 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.
2nd ICHS 11-13/9/2007 Spain 9Copyright; 2007 IAE. All rights reserved.
VentilationVentilation
- 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.
2nd ICHS 11-13/9/2007 Spain 10Copyright; 2007 IAE. All rights reserved.
3. Experimental Procedure3. Experimental Procedure
1600 sec 2400 sec800 sec
Ventilation
Hydrogen release
Gas sampling: 3 sec
Spark Activated: 5 sec,Interval : 5 sec (on the ceiling) 1 sec (next to the nozzle).
0 sec
- 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.
Time sequence of a test
2nd ICHS 11-13/9/2007 Spain 11Copyright; 2007 IAE. All rights reserved.
4. Results4. Results
0
0.1
0.2
0.3
0.4
0.5
0 0.005 0.01 0.015 0.02
Ve
ntila
tion
spe
ed (
m3 /s
)
Hydrogen release rate (m 3/s)
Test 16Test 17
Test 18
Test 19
Test 21
Test 22
Test 23 Test 26
Test 25
Test 24 Test 20
Parameter combination of release experiments
2nd ICHS 11-13/9/2007 Spain 12Copyright; 2007 IAE. All rights reserved.
Release rate and VentilationRelease rate and Ventilation
The hydrogen release rate and ventilation rate were nearly constant for each experiment.
Time (seconds) Time (seconds)
Re
lea
se
rate
(N
m3/s
)
Ve
nti
lati
on
ra
te (
Nm
3/s
)
2nd ICHS 11-13/9/2007 Spain 13Copyright; 2007 IAE. All rights reserved.
Hydrogen densityHydrogen density
0
0.5
1
1.5
2
2.5
3
3.5
4
0 10 20 30 40 50 60Max
imum
hyd
roge
n c
once
ntra
tion
(%)
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.
2nd ICHS 11-13/9/2007 Spain 14Copyright; 2007 IAE. All rights reserved.
Overpressure and impulseOverpressure and impulse
- Hydrogen release rate: 0.02m3/s- 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.
Time (seconds)
Ov
erp
ress
ure
(k
Pa
)Im
pu
lse (k
Pa
-s)
2nd ICHS 11-13/9/2007 Spain 15Copyright; 2007 IAE. All rights reserved.
Flame front velocityFlame front velocity
Time (seconds)
Ra
ng
e (m
)
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.
2nd ICHS 11-13/9/2007 Spain 16Copyright; 2007 IAE. All rights reserved.
0
5
10
15
20
0 0.05 0.1 0.15 0.2
Max
imu
m h
yrdg
en c
once
ntra
tion
(%)
The ratio of hydrogen release rate to ventilation speed
- 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…). The correlation between the ratio of the hydrogen
release rate to ventilation rate and the maximum hydrogen concentration.
Hydrogen concentrationHydrogen concentration
2nd ICHS 11-13/9/2007 Spain 17Copyright; 2007 IAE. All rights reserved.
5. Summary5. 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.
2nd ICHS 11-13/9/2007 Spain 18Copyright; 2007 IAE. All rights reserved.
Acknowledgement Acknowledgement
- Authors would like to thank NEDO for their financial support and fruitful comments.
2nd ICHS 11-13/9/2007 Spain 19Copyright; 2007 IAE. All rights reserved.
Thank you for your kind attention !
2nd ICHS 11-13/9/2007 Spain 20Copyright; 2007 IAE. All rights reserved.
VentilationVentilation- 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