1. www.gexcon.com © GexCon AS JIP Meeting, 12-13 May 2011, Bergen, Norway 1 Ichard M. 1, Hansen O.R. 1, Middha P. 1 and Willoughby D. 2 1 GexCon AS 2 HSL 4 th International Conference on Hydrogen Safety, San Francisco, USA September 12-14, 2011 CFD computations of liquid hydrogen releases

2. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 2 Outline Introduction Previous work with FLACS Multiphase flow modeling in FLACS Simulations of HSL experiments Conclusions

3. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 3 Liquid hydrogen releases Spills of liquid hydrogen are a hazardous scenario in a variety of settings (industrial, transport, etc.) There are still several uncertainties in modelling LH 2 spills Current work uses recent HSL experiments as a basis for evaluating new spill models in FLACS

4. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 4 FLACS CFD code Specifically developed for process safety applications (explosion & dispersion) Shallow water equations solved for liquid spill modelling Obstacles can affect the liquid motion ABL modelled by imposing velocity, temperature & turbulence profiles at inlet boundaries Pasquill-Gifford stability classes used to represent atmospheric stability

5. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 5 Previous work with FLACS The BAM experiments  LH 2 releases between buildings (0.37 kg/s; duration 125 s) The NASA experiments  LH 2 releases on flat terrain (11.5 kg/s; duration 35 s) Significant efforts in LNG related work  Burro, Coyote, Maplin Sands and Wind tunnel experiments simulated (MEP – Hansen et al., 2010)

6. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 6 Multiphase flow modelling in FLACS The Homogeneous Equilibrium Model (HEM) used for modeling two-phase flows Both phases assumed to be in local thermal and kinematic equilibrium Two main advantages:  Limited information about the source is needed  Conservation equations are similar to single phase flow equations One main disadvantage:  The assumption of equilibrium (fails for large particles)

7. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 7 Multiphase flow modelling in FLACS (2) Model for liquid deposition on obstacles Rain-out is due to jet impingement on obstacles: rain-out is controlled by the momentum of the jet The mass of liquid that rains out is directly transferred to the pool model

8. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 8 Experimental Description The HSL experiments (4 tests in total):  2 vertically downward releases 100 mm above ground (Tests 6 and 10)  1 horizontal release 860 mm above ground (Test 7)  1 horizontal release on the ground (Test 5)  Release rate: 60 l/min

9. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 9 Simulations of HSL experiments Estimation of the source term (ST):  Reservoir: P 0 =2 bar T 0 =T sat (P 0 )  Volumetric flow rate known: 60 l/min  Need to obtain the volume fraction of gas at the exit orifice  Sensitivity study - different gas volume fraction assumed at the exit orifice:

10. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 10 Simulations of HSL experiments (2) Approach: Simulate Test 7 and find the most appropriate ST: ST3 or ST4 compare well. Photograph of Test 7 2D cut planes of temperature ST1 ST2 ST3 ST4 ST5

11. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 11 Simulations of HSL experiments (3) Approach: Simulate Test 7 and find the most appropriate ST: ST4 gives the best predictions overall. Profile of minimum temperature along the jet axis, 0.75m above the ground

12. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 12 Simulations of HSL experiments (4) Simulation of Test 6 with ST4:  Downward release 100 mm above the ground  Investigate the effect of air condensation.  Boiling point of O 2 is 90K and N 2 is 77 K  Volume contour plot of temperature at T=77 K: condensing/freezing zone of N 2 and O 2

13. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 13 Simulations of HSL experiments (5) Effect of air condensation (Test 6) Vertical profiles 1.5 m downstream of exit orifice TemperatureVelocity

14. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 14 Simulations of HSL experiments (6) Comparison of temperature time series: 0.25m above ground 0.75m above ground Profiles 1.5m downstream of exit orifice

15. www.gexcon.com © GexCon AS 4 th ICHS, Sep 12-14, 2011 15 Conclusion An approach to simulate two-phase flows and releases of liquid hydrogen has been presented A sensitivity study on the source term has shown the importance of having a proper ST model The condensation of O 2 and N 2 can have non- negligible effects on the flow field Condensation of water vapor may also have non- negligible effects  Will be a part of future investigations

16. www.gexcon.com © GexCon AS JIP Meeting, 12-13 May 2011, Bergen, Norway 16