HIGH PRESSURE HYDROGEN JETS IN THE PRESENCE OF A SURFACE P. Bénard, A. Tchouvelev, A. Hourri, Z. Chen and B. Angers
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 284.42 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
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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 jet Horizontal free jet Vertical surface jet Vertical free jet Hydrogen 171072 114048 435984 444672 Methane 57024 Number of cells in each simulation domain Horizontal surface jet Horizontal free jet Vertical surface jet Vertical free jet x y z x y z x y z x y z Size (m) 115 25 25 115 25 50 15 8.5 201 15 15 101
Horizontal jets
H2 CH4 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
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
* 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
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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 24000 cells.
Maximum LFL distances for hydrogen and methane
Birch : 45 m (H2) – 12.3 m (CH4)
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
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