1. MODELING OF SUDDEN HYDROGEN EXPANSION FROM CRYOGENIC PRESSURE VESSEL FAILURE Guillaume Petitpas and Salvador M. Aceves Lawrence Livermore National Laboratory 7000 East Avenue, L-792 Livermore, CA 94550 USA ID#: 253 September 12-14, 2011 SAN FRANCISCO, USA

2. Cryogenic pressure vessels can store hydrogen at low temperatures with minimum evaporative losses Low heat transfer obtained with “vessel within a vessel” design Conduction: composite supports Convection: vacuum pressure < 1mTorr Radiation: MLI 2

3. Thermodynamic advantages of cryogenic pressure vessels drive superior weight, volume and cost Source: TIAX Source: Argonne National Lab (Ahluwalia et al.), AMR 2011 3

4. Cryogenic pressure vessels’ low operating temperature reduces expansion energy 4

5. High Pressure Vessel MOP: 350 bar Operating T: 20.3 to 300 K Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure Vacuum shell Rupture Discs Burst pressure: 1.5 bar (relative) 5

6. High Pressure Vessel Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure Vacuum shell Rupture Discs Pressure vessel initially full (H 2 density between 28 and 70 g/L) 6

7. High Pressure Vessel Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure Vacuum shell Rupture Discs At t=0 s, an accidental failure happens 7

8. High Pressure Vessel Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure Vacuum shell Rupture Discs Hydrogen starts flowing into the vacuum shell through a 7.62 mm diameter opening (penetration test FMVSS 304) 8

9. High Pressure Vessel Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure Vacuum shell Rupture Discs When the pressure in the vacuum shell reaches 1.5 bar, the rupture discs break and H 2 flows in the atmosphere 9

10. Governing equations Adiabatic release: no heat transfer between gas and containers Orifices at choked condition throughout the process, no slip Expansion takes place in small region near the orifice, modeled by a quasi 1D isentropic flow Real gas behavior, using REFPROP Version 8.0 Calculation ends when vacuum shell reaches atmospheric pressure 10 We have developed a transient H 2 release model

11. Initial conditions in the vessel : 350 bar, 300 K Choked flow for a single vessel is determined using initial stagnation state, assuming isentropic flow Throat P t, T t, s t =s Vessel P,T,s At maximum flow rate, M=1 (velocity= local speed of sound) 11

12. Thermodynamic state at the throat can be “mapped” for different initial vessel conditions 12

13. Step 1: Determine choked conditions at the throat for stagnation state down to 0.7*T c 13

14. Hydrogen release from 350 bar, 300 K 14 Step 2: Apply those calculations to the accidental release of H 2 in a cryogenic pressure vessel

15. 15 Results indicate that a vessel initially at room temperature does not experience phase change Hydrogen release from 350 bar, 300 K

16. 16 H 2 initially at cryogenic temperature depressurizes faster, phase change occurs in the pressure vessel Hydrogen release from 350 bar, 62 K (70 g/L)

17. 17 Vent pressure is ~10X lower for cryogenic vessels vs. room temperature compressed gas vessel

18. 18 Vent energy is 10X lower for cryogenic vessels vs. room temperature compressed gas vessel Energy released in 1 second: Room Temp 150 Wh/kgH 2 Cryogenic 15 Wh/kgH 2

19. 19 Summary We have modeled 2-phase choking states down to 0.7*T c Choked flow model has been applied to accidental release from “vessel within a vessel” cryogenic storage Vent energy and pressure from cryogenic pressure vessel failure is 10 times lower than for compressed gas tanks, reducing hazards to surrounding people and property