1. HOMOGENEOUS HYDROGEN DEFLAGRATIONS IN SMALL SCALE ENCLOSURE
HOMOGENEOUS HYDROGEN DEFLAGRATIONS IN SMALL SCALE ENCLOSURE. EXPERIMENTAL RESULTS
Martino Schiavetti, Tommaso Pini, Marco Carcassi
Department of Civil and Industrial Engineering (DICI)
University of Pisa

2. Presentation overview:
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Presentation overview:
Introduction
Small Scale Enclosure Design
Variables under investigation
Test matrix
Results
Vent opening pressure and behavior (plastic+ FIKE)
Max overpressure vs. plastic sheet configuration
Max overpressure vs. vent location
Max overpressure vs. Obstacle configuration
Max overpressure vs. Ignition location
Pressure peaks (3rd local pressure peak)
ICHS, Hamburg (Germany) September,

3. Introduction HySEA projects objectives include:
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Introduction
HySEA projects objectives include:
To perform experiments in real-life enclosures and containers with industry-representative obstacles in hydrogen energy applications;
To characterize different venting systems (e.g. doors, natural vent openings, etc.) and include measurements of structure response in these tests;
WP-2.2: Explosion experiments with homogeneous mixtures in small-scale enclosures
HySEA-D Small-scale enclosure dimension and design
HySEA-D Small-scale enclosure Experimental campaign of hydrogen deflagrations for homogeneous H2 concentrations
“…design a generic experimental enclosure suitable for investigating vented hydrogen explosions in installations such as gas cabinets, cylinder enclosures, dispensers and backup power systems.”
ICHS 2017, Hamburg (Germany) September, 11-13

4. Small Scale Enclosure design
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Small Scale Enclosure design
Height – 2000 mm
Width – 920 mm
Depth – 620 mm
l = 50 mm
a = 4 mm
Vent dimensions
b = 500 mm
c = 800 mm
ICHS 2017, Hamburg (Germany) September, 11-13

5. Small Scale Enclosure design
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Small Scale Enclosure design
Pressure transducer (Side)
Pressure transducers:
Bottom: Center of the floor
Side: On the centerline of the back plate 1.5 m above the floor
Hydrogen release hole
Pressure transducer (Bottom)
Fan
Internal camera
External camera
Pressure acquisition:
5 kHz
Video recording: 240 frames per second
ICHS 2017, Hamburg (Germany) September, 11-13

6. Small Scale Enclosure design
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Small Scale Enclosure design
5 Sampling locations
Ignition location:
Bottom:
On the centerline 0.5m above the floor
Centre:
On the centerline 1m above the floor
Top:
On the centerline 1.5 m above the floor
3 Ignition
locations
ICHS 2017, Hamburg (Germany) September, 11-13

7. Variables under investigation
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Variables under investigation
Hydrogen concentration:
between 10%vol. and 18%vol.
Vent location:
the two possible locations of the vent area are on the top and on the upper front wall of the enclosure (only one of the two is used in each test)
Vent type:
three different types of FIKE explosion vent had been tested as well as a plastic sheets in different configurations (the plastic sheet had been cut in order to lower its opening pressure and avoid plastic deformation before rupture)
Ignition location:
The flammable mixture could be ignited along the centreline of the enclosure at three different heights (top, middle and bottom part of the enclosure)
Internal obstacle configuration:
Empty enclosure has been studied as reference case, than one or three gas bottles were placed inside the enclosure to study the effect of the congestions on the deflagrations.
ICHS 2017, Hamburg (Germany) September, 11-13

8. Variables under investigation Vent location Vent type
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Variables under investigation
Vent location
Vent type
Plastic sheets
FIKE vents
Top vent 1 1
Area: 0.4 m2
Area: 0.4 m2
P open: mbar 2 2
Area: 0.4 m2
Cut along the perimeter (sealed by paper tape)
Area: 0.4 m2
P open: mbar
Front vent 3 3
Area: 0.4 m2
Cross cut (sealed by paper tape)
Area: 0.4 m2
P open: mbar
ICHS 2017, Hamburg (Germany) September, 11-13

9. Variables under investigation Internal obstacle configuration
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Variables under investigation
Internal obstacle configuration
Empty SSE
1 bottle
3 bottles
Free volume~1.141 m3
Free volume~1.085 m3
Free volume~0.974 m3
Volume reduction 4.86%
Volume reduction 14.58%
ICHS 2017, Hamburg (Germany) September, 11-13

10. Experimental campaign
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Experimental campaign
Total number of tests 76
Tests with homogeneous concentration 74
Bottom pressure time history
Side pressure time history
Mechanical displacement measurement 19
Laser displacement measurement 49
Lower front plate
Plate centre 11
93.1 cm 2
111.45 10
Upper front plate 26
Tightening torque
50 N-m 14
80 N-m 6
20 N-m
Flame video recording
(Aerosol dispersion of salty water)
Lateral view 20
Internal view 24
Vent video recording 42 37
35 (43)
Displacement video recording
(During mechanical measurements) 8
ICHS 2017, Hamburg (Germany) September, 11-13

11. Experimental campaign Presentation of results
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Experimental campaign
Presentation of results
Test #
H2 concentration
Vent
Loc.
Vent type
Ignit.
Locat.
Obstacle conf.
Vent opening press.
Pb/Ps
[mbar]
Max peak press. Pb/Ps
Test plate
# / thickness
Displ. Locat.
Max displ.
[mm]
Displ. time hist.
NOTES
Sampl. location [%vol.]
Aver.
[%vol.]
TP01
12.0%
11.9
Top vent
Plastic sheet 1
Bottom (#2)
Empty
23.7/21.9
23.7/21.9 (3)(4)
1 / 2mm
Plate centre 12 NO
11.8%
11.9%
12.2%
TP02
13.8%
13.8
27.9/25.7
31.4/26.8 18
13.9%
13.6%
14.1%
TP03
15.4%
15.53
44.2/35.1
60.2/49.2 17
15.6%
15.3%
15.95%
TP04
14%
14.3
Centre
(#3)
41.6/36.7
41.6/36.7 (3)(4)
14.5%
14.6%
ICHS 2017, Hamburg (Germany) September, 11-13

12. Plastic sheet configuration 1
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Plastic sheet configuration 1
Vent opening pressure and behavior
Plastic sheet configuration 3
ICHS 2017, Hamburg (Germany) September, 11-13

13. Vent opening pressure and behavior (plastic sheets)
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Vent opening pressure and behavior (plastic sheets)
The opening pressure increases when increasing hydrogen concentration.
Even though plastic sheet has a very low opening inertia its behavior is affected by the reactivity of the mixture
Obstacle configuration affects the opening pressure of the plastic sheet, reducing the free volume inside the SSE the opening pressure increases
ICHS 2017, Hamburg (Germany) September, 11-13

14. Peak pressure difference
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Vent Opening (FIKE ) (Test TP20 – H2 conc. 14.1%vol. – bottom ignition)
Complete detachment
(~3 frames ) (~0.012 seconds )
Typical
P-T history
Vent starts to open (frame 0)
Vent open completely (frame 3)
Pbottom - Pside
Peak pressure difference
Vent area completely free (frame 10)
Vent area completely free
(~10 frames )
(~ seconds)
ICHS 2017, Hamburg (Germany) September, 11-13

15. Vent opening pressure (FIKE vents)
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Vent opening pressure (FIKE vents)
Popen: mbar
Popen: mbar
Opening pressure plate data for commercial vents refers to «static pressure»
Popen: mbar
[bar/s]
ICHS 2017, Hamburg (Germany) September, 11-13

16. Maximum overpressure vs. Vent location
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Tests performed with the same vent characteristics and opening features were compared to investigate the dependence of the maximum peak pressure with the vent location
Results
Maximum overpressure vs. Vent location
In the configurations with the empty facility top vent is more effective in mitigating the maximum overpressure but results are comparable with the one of the front vent (max ΔP 20 mbar at 16% average concentration)
3 bottles
Empty
In the configuration with 3 bottles inside the facility the front vent is more effective than the top one in mitigating the internal maximum overpressure
ICHS 2017, Hamburg (Germany) September, 11-13

17. Maximum overpressure vs. Vent location
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Maximum overpressure vs. Vent location
Empty
In the configurations with the empty facility and with 1 bottle inside the SSE vents located on top or front of the facility are comparable in mitigating the generated overpressure
3 bottles
All ignition locations
1 bottle
In the configuration with 3 bottles inside the SSE the front vent is more effective than the top one in mitigating the internal maximum overpressure
ICHS 2017, Hamburg (Germany) September, 11-13

18. Maximum overpressure vs. Obstacle configuration
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Maximum overpressure vs. Obstacle configuration
All ignition locations
For the empty SSE the maximum peak overpressure is lower than the one obtained in configurations where 1 or 3 bottles are placed inside
Front vent
Only Bottom ignition
Front vent
Results of tests performed with 1 or 3 bottles produced comparable overpressures
ICHS 2017, Hamburg (Germany) September, 11-13

19. Maximum overpressure vs. Obstacle configuration
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Maximum overpressure vs. Obstacle configuration
Top vent - All ignition locations
For top vent location a slight dependence of the maximum peak overpressure with obstacle configuration has been found
Top vent - Only Bottom ignition
The maximum peak overpressure increases when increasing the degree of congestion inside the facility
ICHS 2017, Hamburg (Germany) September, 11-13

20. Maximum overpressure vs. Ignition location
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Maximum overpressure vs. Ignition location
Front vent :
Center ignition location is closer to the vent surface than in top vent configurations
Center ignition produces lower maximum peak overpressure with respect to bottom ignition
Top and center ignition are both “close vent ignitions”
Front vent
Top vent:
Top ignition always produces lower overpressures
Bottom and center ignition produce comparable results (Empty + 1 bottle)
ICHS 2017, Hamburg (Germany) September, 11-13

21. Maximum overpressure vs. Ignition location (Top vent) Empty
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Maximum overpressure vs Ignition location (Top vent)
Empty
1 bottle
The behavior seems not to be confirmed for obstacle configuration where 3 bottles are placed inside the facility
Despite only one test was ignited from the centre location, the resulting overpressure is much lower than the one obtained igniting from the bottom
When venting through the top, bottom and center ignition produce comparable results (maximum overpressure), while top ignition always produces lower overpressures
3 bottles
ICHS 2017, Hamburg (Germany) September, 11-13

22. Deflagration Pressure peaks
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
Results
Deflagration Pressure peaks
The 3rd peak is always higher at Pbottom (often not the dominant one at Pside)
Some of the tests showed a number of pressure peaks after the so called “2nd peak”. Of these peaks, the first one, identified as 3rd peak, may be higher than the 2nd peak (Pext)
ICHS 2017, Hamburg (Germany) September, 11-13

23. Homogeneous hydrogen deflagrations in small scale enclosure
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
HySEA CONSORTIUM
ICHS 2017, Hamburg (Germany) September, 11-13

24. Homogeneous hydrogen deflagrations in small scale enclosure
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
ACKNOWLEDGEMENTS
The HySEA project received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU) under grant agreement No
This Joint Undertaking received support from the European Union’s Horizon 2020 research and innovation programme and United Kingdom, Italy, Belgium and Norway.
ICHS 2017, Hamburg (Germany) September, 11-13

25. THANK YOU FOR YOUR ATTENTION!
Homogeneous hydrogen deflagrations in small scale enclosure. Experimental results
THANK YOU FOR YOUR ATTENTION!
ICHS 2017, Hamburg (Germany) September, 11-13