1. 0 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Study of Hydrogen Diffusion and Deflagration in a Closed System Yuki Ishimoto 1, Erik Merilo 2, Mark Groethe 2, Seiki Chiba 3, Hiroyuki Iwabuchi 1, Ko Sakata 1 1 The Institute of Applied Energy, Japan 2 SRI International, USA 3 SRI International, Japan Poulter Laboratory

2. 1 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 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”.

3. 2 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 1.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. 37m 3 300m 3 Tunnel 76m long Facilities for hydrogen deflagration research Our early study and motivation;

4. 3 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 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.

5. 4 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 2. Experimental facility Dimensions - Height: 2.72 m - Width: 3.64 m - Length: 6.10 m - Volume: ~60 m 3 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

6. 5 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 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.

7. 6 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Measurements - 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 Thermocouples Spark ignition module Thermocouple Spark ignition module Release nozzle Thermocouple

8. 7 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Gas sampling system Sampling SetupMeasurement 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.

9. 8 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 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.

10. 9 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 3. Experimental Procedure 1600 sec2400 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

11. 10 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 4. Results Parameter combination of release experiments

12. 11 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Release rate and Ventilation The hydrogen release rate and ventilation rate were nearly constant for each experiment. Time (seconds) Release rate (Nm 3 /s) Ventilation rate (Nm 3 /s)

13. 12 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Hydrogen density - 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.

14. 13 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Overpressure and impulse - Hydrogen release rate: 0.02m 3 /s - Ventilation rate: 0.1m 3 /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) Overpressure (kPa) Impulse (kPa-s)

15. 14 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Flame front velocity Time (seconds) Range (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.

16. 15 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain - 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 concentration

17. 16 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 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: 60m 3 ). - The hydrogen release rate ranged from 0.002 m 3 /s to 0.02 m 3 /s. The ventilation rate varied from 0.1 m 3 /s to 0.4 m 3 /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.

18. 17 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Acknowledgement - Authors would like to thank NEDO for their financial support and fruitful comments.

19. 18 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Thank you for your kind attention !

20. 19 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain 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

21. 20 Copyright; 2007 IAE. All rights reserved. 2nd ICHS 11-13/9/2007 Spain Cross-sectional schematic of the facility Open end: film 6.1m Spark module Nozzle H2H2 Inlet Outlet 1 2 3 Gas sampling Pressure transducer 2.72m