HIGH PRESSURE HYDROGEN JETS IN THE PRESENCE OF A SURFACE P. Bénard, A. Tchouvelev, A. Hourri, Z. Chen and B. Angers

Objective Birch/Sandia approach has been proposed to estimate distances from leak to specified concentration levels and clearance distances from hydrogen jet flames This project aims to ◦ Study the effects of surfaces and transients on the extent of hydrogen releases ◦ Examine limits to engineering correlations of maximum extent of hydrogen jets

Surface jet studies Preliminary studies We consider ◦ Horizontal and vertical jets ◦ Steady-state jet Approach: CFD sims of hydrogen and methane jets using FLACS, Phoenics and Fluent Specific case considered ◦ Diameter of the release is 8.48 mm ◦ Storage pressure is bar ◦ Flow rate is 0.98 kg/s for hydrogen and 2.72 kg/s for methane Assume release from a PRD at 1 m from vertical or horizontal surface 3

FLACS simulations Finite volume solver with SIMPLE pressure-velocity correction extended for compressible flows k- ε turbulent model and ideal gas equation of state Jet outlet conditions are calculated using an imbedded jet program ◦ Pseudo source approach  Similar to Birch method Size of the simulation domains Horizontal surface jetHorizontal free jetVertical surface jetVertical free jet Hydrogen Methane57024 Number of cells in each simulation domain Horizontal surface jetHorizontal free jetVertical surface jetVertical free jet xyzxyzxyzxyz Size (m)

Horizontal jets H2H2 CH 4 Extent: 35 m (after 20 sec) Transient: 36.5 m at 10.1 sec Extent: 45 m (steady state after 24 sec) Transient: 52.5 m at 14 sec Extent: 15.5 m (steady-state after 15 sec) Extent: 33.6 m (steady state after15 sec) Transient: 33.8 m (at 11 sec) Birch prediction: 45 m Birch prediction: 12.3 m

Transient behavior – steady-state horizontal jets (FLACS)

Transient behavior 700 bar – 0.50 m from ground ◦ Time dependent release Fluent (RNG k-  ) ◦ Same maximum extent & duration with FLACS

Vertical surface jet - hydrogen Free jet/Flacs: 42.4 m – no significant transient Wall/Flacs: 95.8 m – transient max: 112 m Birch: 45 m

Vertical surface jet - methane Free jet: 15.5 m Surface jet: 32 m Max transient extent (surface jet): 36.4 m Birch prediction: 12.3 m Unlike horizontal jets, a transient max extent is observed for vertical methane jets 9 Surface jet Side view Free vertical jet Top view

Results – Horizontal jets Steady-state extents: ◦ Some discrepancy for hydrogen with Birch predictions (expected) ◦ Large enhancement of the extent of the flammable envelope (  30%) for surface hydrogen jets ◦ Larger (absolute and relative) enhancement observed for methane (increase by a factor of 2.3) Transient behavior: ◦ Significant short duration enhancement of the extent with respect to the steady-state observed for hydrogen (20%) ◦ No transient effect observed for methane 10

Results – Vertical jets Steady-state extents: ◦ Overall good agreement with Birch predictions ◦ Large enhancement of the extent of the flammable envelope (factor of 2.5) for surface hydrogen jets ◦ Important enhancement of the extent for methane (factor of  2) is also observed  Similar increase as horizontal surface jet  Buoyancy effects less important for methane than hydrogen for the flow rate considered Transient behavior: ◦ Transient increase of the flammable extent is observed for hydrogen ◦ Some transient effect is observed for methane depending on the model (3-12%)

PHOENICS Simulations Constant release rate, transient dispersion mode, k- ε RNG turbulence model with real or effective orifice (calculated with 1984 Birch approach). Symmetric domain of 100 m × 8 m × 25 m (except for ground vertical hydrogen jet 130 m × 8 m × 25 m) with structured mesh of cells.

Maximum LFL distances for hydrogen and methane Scenarios Jet typeFree jetSurface jet OrificeRealEffectiveRealEffective Direction of releaseHorizontal VerticalHorizontal Vertical H2H2 AVT Max. Extent32.5 m43.5 m44.5 m45.5 m63.4 m109 m Steady State Max. Extent32.5 m43.5 m44.5 m45.5 m50.2 m109 m Centerline21.5 m38.1 m44.5 m38.4 m42.4 m79.5 m HRI Max. ExtentN/A36.5 m42.7 mN/A52.5 m112.3 m Steady State Max. ExtentN/A35.0 m42.4 mN/A44.9 m95.8 m CenterlineN/A22.8 m42.4 mN/A40.1 m80.2 m CH 4 AVT Max. Extent13.2 m18.3 m 34.1 m38.5 m39.0 m Steady State Max. Extent13.2 m18.2 m18.3 m34.1 m38.5 m38.0 m Centerline13.1 m18.1 m18.3 m20.8 m21.0 m21.1 m HRI Max. ExtentN/A14.9 m15.5 mN/A33.8 m36.4 m Steady State Max. ExtentN/A14.9 m15.5 mN/A33.6 m32.0 m CenterlineN/A14.7 m15.5 mN/A20.3 m19.8 m Birch : 45 m (H 2 ) – 12.3 m (CH 4 )

Conclusion Overall convergence of results for steady-state régime ◦ Some model dependence but ballpark agreement Transient extents are very probably unreliable – model, mesh and numerics dependent ◦ Important to quantify accurately Implications for Codes and Standards ◦ Reliability of clearance distance calculations based on steady-state correlations (Birch et al) because of transient increase of the extent of the flammable envelope? ◦ Clearance from surfaces criterion for vents/PRD?

Further work Validation experiments are planned Comparison of effective diameter approach Systematic study of the effect of the height Study of transient effects with more elaborate turbulence scheme is necessary