CFD computations of liquid hydrogen releases 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.2 1GexCon AS 2HSL 4th International Conference on Hydrogen Safety, San Francisco, USA September 12-14, 2011

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

Liquid hydrogen releases 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

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

Previous work with FLACS 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)

Multiphase flow modelling in FLACS 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)

Multiphase flow modelling in FLACS (2) 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

Experimental Description 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

Simulations of HSL experiments 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:

Simulations of HSL experiments (2) 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

Simulations of HSL experiments (3) 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

Simulations of HSL experiments (4) 4th ICHS, Sep 12-14, 2011 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 O2 is 90K and N2 is 77 K Volume contour plot of temperature at T=77 K: condensing/freezing zone of N2 and O2

Simulations of HSL experiments (5) 4th ICHS, Sep 12-14, 2011 Simulations of HSL experiments (5) Effect of air condensation (Test 6) Condensation of O2 and N2 releases energy close to the ground and generates an upward velocity that brings cold hydrogen gas to higher altitudes Temperature Velocity Vertical profiles 1.5 m downstream of exit orifice

Simulations of HSL experiments (6) 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

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

JIP Meeting, 12-13 May 2011, Bergen, Norway