V. Shentsov, M. Kuznetsov, V. Molkov 6th International Conference on Hydrogen Safety, 19-21 October, 2015, Yokohama, Japan The pressure peaking phenomenon: validation for unignited releases in laboratory-scale enclosure V. Shentsov, M. Kuznetsov, V. Molkov Hydrogen Safety Engineering and Research Centre (HySAFER)

Presentation outline What is pressure peaking phenomenon (PPP) Calculation of PPP: 2 steps methodology Experimental facility and validation tests at KIT Ulster theory versus KIT experiments Conclusions

The problem Hydrogen stored as compressed gas @ 350-700 bar Even if unignited, the release of hydrogen has been shown to result in unacceptable overpressures indoors capable of destroying the structure (pressure peaking phenomenon, see Brennan & Molkov, 2013) The experimental results were absent for PPP validation before the project www.hyindoor.eu This study presents the experimental validation of PPP existence and the Ulster theory validation

The pressure peaking phenomenon Example of garage Typical garage of size LxWxH=4.5x2.6x2.6 m with a “brick” size vent. Mass flow rate 390 g/s (350 bar, 5.08 mm TPRD orifice). Pressure limit for structures to withstand Engineering solution: decrease PRD orifice size (by increasing fire resistance of storage tank)

2-steps methodology Cyber-laboratory (free access) Step 1: Make an estimation of PPP existence inside the compartment of interest. PPP exists only when hydrogen leak and vent size are such that there will be only outflow of hydrogen through the vent outside the enclosure, i.e. 100% hydrogen accumulation with time will be reached. Calculate hydrogen concentration in an enclosure using nomogram/model (Molkov et. al 2014) or engineering tool www.h2fc.eu/cyber-laboratory. If the calculated concentration is 100% then the second step has to be applied to calculate the PPP overpressure. Step 2: Use the model/nomogram (Brennan and Molkov 2013) implemented as an engineering tool at www.h2fc.eu/cyber-laboratory to calculate the over-pressure resulting from PPP.

Experimental facility (KIT) Validation tests 19 experiments on PPP were carried out by KIT (Germany) in the enclosure with sizes HxWxL=1x0.98x0.96 m. Round vent of diameter either 11 mm or 16.5 mm was located centrally at the top of the front panel or at the bottom. Three gases were tested: air, helium and hydrogen Internal diameter of the release nozzle is specified to 5 mm, located at the centre of enclosure 10 cm above the floor directed vertically. Release rates ranges 0.1-2.8 g/s. Rear wall Left wall Front wall

Validation Air and helium releases Air, 1.444 g/s, CD=0.72 Helium, 0.22 g/s, Top vent 0.95 cm2, CD=0.72 Helium, 0.22 g/s Bottom vent, CD=0.72 WP1 - Task 1.1 - Presentation title

Validation Helium releases PPP is independent on vent location Helium, 0.985 g/s Bottom vent Vent 0.95 cm2, CD=0.85 Helium, 0.985 g/s, Top vent 0.95 cm2, CD=0.82 Helium, 1 g/s, Vent 2.14 cm2,CD=0.72 Helium, 0.5 g/s, Vent 0.95, CD=0.72 WP1 - Task 1.1 - Presentation title PPP is independent on vent location

Validation Hydrogen releases Hydrogen, 0.108 g/s Vent 0.95 cm2 CD=0.65 Due to higher pressure the experimental enclosure starts to “breathe” resulting in the additional vent area increase of 0.8 cm2 Hydrogen, 1.08 g/s Vent 2.14 cm2, CD=0.9 Hydrogen, 1.08 g/s Vent 0.95 cm2,CD=0.72 WP1 - Task 1.1 - Presentation title

Validation Effect of “breathing” on CD Hydrogen, 0.549 g/s Vent 2.14 cm2, CD=0.54 Hydrogen, 0.108 g/s Vent 0.95 cm2, CD=0.56 The CD scatter 0.54-0.9 is thought due to the “breathing” of the enclosure, i.e. the existence of “additional openings” (non-controllable process) will be “compensated” in the calculations by larger value of discharge coefficient CD. WP1 - Task 1.1 - Presentation title

Leak in fully “closed” box “Breathing” effect Closed camera Leak in fully “closed” box Hydrogen, 0.287 g/s Maximum opening of 0.67 cm2 with CD=0.72 WP1 - Task 1.1 - Presentation title

Concluding remarks Experiments with release of air, helium and hydrogen performed by KIT proved the existence of the pressure peaking phenomena predicted theoretically at Ulster in 2013. The discharge coefficient was found to be in the range CD=0.54-0.90 for performed experiments (“breathing effect”). The average value of CD through the series of test is CD=0.72, the conservative value is CD=0.54. PPP should be considered as an essential part of hydrogen safety engineering for all indoor use of HFC systems.

Acknowledgements Thank you for attention! The authors would like to acknowledge the financial support of Fuel Cells and Hydrogen Joint Undertaking under the HyIndoor project (grant agreement No. 278534), and the European Commission for funding through H2FC project.