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CFD computations of liquid hydrogen releases

CFD computations of liquid hydrogen releases. 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. Outline. Introduction Previous work with FLACS

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CFD computations of liquid hydrogen releases

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  1. JIP Meeting, 12-13 May 2011, Bergen, Norway CFD computations of liquid hydrogen releases Ichard M.1, Hansen O.R.1, Middha P.1 and Willoughby D.21GexCon AS2HSL4th International Conference on Hydrogen Safety, San Francisco, USASeptember 12-14, 2011

  2. 4th ICHS, Sep 12-14, 2011 Outline • Introduction • Previous work with FLACS • Multiphase flow modeling in FLACS • Simulations of HSL experiments • Conclusions

  3. 4th ICHS, Sep 12-14, 2011 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 LH2 spills • Current work uses recent HSL experiments as a basis for evaluating new spill models in FLACS

  4. 4th ICHS, Sep 12-14, 2011 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. 4th ICHS, Sep 12-14, 2011 Previous work with FLACS • The BAM experiments • LH2 releases between buildings (0.37 kg/s; duration 125 s) • The NASA experiments • LH2 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. 4th ICHS, Sep 12-14, 2011 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. 4th ICHS, Sep 12-14, 2011 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. 4th ICHS, Sep 12-14, 2011 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. 4th ICHS, Sep 12-14, 2011 Simulations of HSL experiments • Estimation of the source term (ST): • Reservoir: P0=2 bar T0=Tsat(P0) • 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. 4th ICHS, Sep 12-14, 2011 Simulations of HSL experiments (2) • Approach: Simulate Test 7 and find the most appropriate ST: • ST3 or ST4 compare well. ST1 ST2 ST3 2D cut planes of temperature ST4 Photograph of Test 7 ST5

  11. 4th ICHS, Sep 12-14, 2011 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. 4th ICHS, Sep 12-14, 2011 Simulations of HSL experiments (4) • Simulationof Test 6 with ST4: • Downwardrelease 100 mm abovetheground • Investigatetheeffectof air condensation. • Boiling point of O2 is 90K and N2 is 77 K • Volume contour plot oftemperature at T=77 K: condensing/freezingzoneof N2 and O2

  13. 4th ICHS, Sep 12-14, 2011 Simulations of HSL experiments (5) • Effect of air condensation (Test 6) Temperature Velocity Vertical profiles 1.5 m downstream of exit orifice

  14. 4th ICHS, Sep 12-14, 2011 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. 4th ICHS, Sep 12-14, 2011 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 O2 and N2 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. JIP Meeting, 12-13 May 2011, Bergen, Norway

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