high pressure hydrogen jets in the presence of a surface p. bénard, a. tchouvelev, a. hourri, z....
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HIGH PRESSURE HYDROGEN HIGH PRESSURE HYDROGEN JETS IN THE PRESENCE OF A JETS IN THE PRESENCE OF A SURFACESURFACE
P. Bénard, A. Tchouvelev, A. Hourri, Z. Chen and B. Angers
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ObjectiveObjectiveBirch/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
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Surface jet studiesSurface jet studiesPreliminary studiesWe 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
methaneAssume release from a PRD at 1 m from
vertical or horizontal surface
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FLACS simulationsFLACS simulationsFinite 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 methodSize of the simulation domains
Horizontal surface jet Horizontal free jet Vertical surface jet Vertical free jet
Hydrogen 171072114048 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
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Horizontal jetsHorizontal 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
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Transient behavior – steady-Transient behavior – steady-state horizontal jets (FLACS)state horizontal jets (FLACS)
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Transient behaviorTransient behavior 700 bar – 0.50 m from ground
◦ Time dependent release
Fluent (RNG k-) ◦ Same maximum extent & duration with FLACS
0
10
20
30
40
50
60
70
0 5 10 15 20
Time (sec)
Position(m)
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Vertical surface jet - Vertical surface jet - hydrogenhydrogen
Free jet/Flacs: 42.4 m – no significant transient Wall/Flacs: 95.8 m – transient max: 112 mBirch: 45 m
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Vertical surface jet - Vertical surface jet - methanemethane
Free jet: 15.5 mSurface jet: 32 mMax transient extent (surface jet): 36.4 mBirch prediction: 12.3 mUnlike horizontal jets, a transient max extent is observed for vertical methane jets
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Surface jet
Side viewFree vertical jet Top view
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Results – Horizontal jetsResults – Horizontal jetsSteady-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 jetsResults – 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%)
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PHOENICS SimulationsPHOENICS SimulationsConstant 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.
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Maximum LFL distances for Maximum LFL distances for hydrogen and methanehydrogen and methane
Birch : 45 m (H2) – 12.3 m (CH4)
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ConclusionConclusionOverall convergence of results for steady-
state régime◦ Some model dependence but ballpark
agreementTransient 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?
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Further workFurther workValidation experiments are
plannedComparison of effective diameter
approachSystematic study of the effect of
the heightStudy of transient effects with
more elaborate turbulence scheme is necessary