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Study of Hydrogen Diffusion and Deflagration in a Closed System

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. Outline.

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Study of Hydrogen Diffusion and Deflagration in a Closed System

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  1. Study of Hydrogen Diffusion and Deflagration in a Closed System Yuki Ishimoto1, Erik Merilo2, Mark Groethe2, Seiki Chiba3, Hiroyuki Iwabuchi1, Ko Sakata11The Institute of Applied Energy, Japan2SRI International, USA3SRI International, Japan Poulter Laboratory

  2. Outline • Introduction • - Our early studies, motivation and objective • Experimental facility • Facility • Measurement • Experimental Procedure • Results • Summary Studies were administered through NEDO as part of the “Establishment of Codes & Standards for Hydrogen Economy Society”.

  3. 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. Tunnel 76m long 37m3 300m3 Facilities for hydrogen deflagration research

  4. 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. 1.22m 0.09m 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 - 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.

  6. 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. Measurements Thermocouple Release nozzle Spark ignition module Sample stations Sample stations Thermocouple Sample stations - 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. Thermocouples Spark ignition module Thermocouples

  8. Sampling Evacuated Gas sampling system Sampling Setup Measurement Analysis Setup - After the experiment the bottle was attached to the setup to be analyzed. - The absolute pressure and hydrogen partial pressure were recorded. - The bottle was evacuated before the experiment. - The mixture was sampled when valve was 3 was opened - 3 bottles make up one sampling system.

  9. 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. Hydrogen release Gas sampling: 3 sec Spark Activated: 5 sec,Interval : 5 sec (on the ceiling) 1 sec (next to the nozzle). 3. Experimental Procedure Time sequence of a test 0 sec 800 sec 1600 sec 2400 sec Ventilation - 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.

  11. 4. Results Parameter combination of release experiments

  12. Release rate and Ventilation Ventilation rate (Nm3/s) Release rate (Nm3/s) Time (seconds) Time (seconds) The hydrogen release rate and ventilation rate were nearly constant for each experiment.

  13. 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. Overpressure and impulse Overpressure (kPa) Impulse (kPa-s) Time (seconds) - 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.

  15. Flame front velocity Range (m) 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.

  16. 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…). The correlation between the ratio of the hydrogen release rate to ventilation rate and the maximum hydrogen concentration.

  17. 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.

  18. Acknowledgement - Authors would like to thank NEDO for their financial support and fruitful comments.

  19. Thank you for your kind attention !

  20. 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. Cross-sectional schematic of the facility Gas sampling Spark module 2 1 3 Open end: film Outlet H2 2.72m Pressure transducer Inlet 6.1m Nozzle

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