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

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

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

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

Transient behavior – steady-Transient behavior – steady-state horizontal jets (FLACS)state horizontal jets (FLACS)

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)

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

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

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%)

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.

Maximum LFL distances for Maximum LFL distances for hydrogen and methanehydrogen and methane

Birch : 45 m (H2) – 12.3 m (CH4)

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?

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