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Flammable extent of hydrogen jets close to surfaces Benjamin Angers*, Ahmed Hourri*, Luis Fernando Gomez, Pierre Bénard and Andrei Tchouvelev** * Hydrogen.

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Presentation on theme: "Flammable extent of hydrogen jets close to surfaces Benjamin Angers*, Ahmed Hourri*, Luis Fernando Gomez, Pierre Bénard and Andrei Tchouvelev** * Hydrogen."— Presentation transcript:

1 Flammable extent of hydrogen jets close to surfaces Benjamin Angers*, Ahmed Hourri*, Luis Fernando Gomez, Pierre Bénard and Andrei Tchouvelev** * Hydrogen Research Institute, Université du Québec à Trois-Rivières, Trois- Rivières, Québec Canada (G9A 5H8) **A.V.Tchouvelev & Associates, Mississauga, Ontario, Canada International Conference on Hydrogen Safety, San Francisco, September

2 Project objective Molar concentration envelopes can be used to define clearance distances and exclusion zones based on the prevention of ignition (typical values: 2%, 4%, 8%) Jet releases constitute one of the more basic process through which hydrogen releases disperses in air The behavior of the expanded region of vertical jets is well understood and can be treated analytically ◦ Vertical jet release properties (concentration profile) can be calculated from the storage conditions The effect of surfaces will significantly alter their predictions The objective of this work is to quantify the effect of surfaces on unignited hydrogen jets and find engineering correlations that could be used to establish the flammable extent of jet releases in the presence of surfaces Top Side

3 Surface jet studies In this work we consider ◦ Vertical transient jets ◦ Subsonic horizontal jets Approach: CFD sims of Hydrogen and Methane jets using FLACS (numerical efficiency) and Fluent (more control over models) In terms of the cases considered ◦ Vertical jets  GexCon FLACS, k- , sonic release using a pseudo-diameter approach based on conservation laws and the Hugoniot relations ◦ Horizontal jets  Fluent, RNG k- , subsonic 3

4 Hydrogen & methane jets Flacs bars (H2) Vertical jets

5 Gas Storage pressure (barg) Mass Flow rate (kg/s) Jet exit distance from the surface (m) H from m to 10 m from m to 10 m from m to 10 m from m to 10 m from m to 12 m CH from m to 4 m from m to 4 m from m to 5 m from m to 5 m from m to 10 m Vertical jets (d=6.38 mm, T=298 K) Cases considered

6 free jet m from surface Results for hydrogen bars

7 Summary results for hydrogen Steady decrease to free jet values for centerline Crossover behaviour for maximum extent due to proximity of the surface

8 Normalized relative extent Pressure (barg) X free_jet (m)X abs_max - X free_jet (m)h (m) at NRE(h) = NRE(h) = (X max (h) - X free_jet )/(X abs_max - X free_jet )

9 Results for methane Larger effect of the surface for methane (relative) Reversed amplitude in the crossover region NRE (Max extent) > NRE (Centerline) Reserved effect not observed in 0 G simulations

10 Normalized extent of zero G jet Centerline extent and max extent normalized axes for 100 bar, 250 bar, 400 bar, 550 bar and 700 bar release, with no gravity. Hydrogen Methane

11 Horizontal subsonic jets : Surface jets studies of hydrogen using Fluent Subsonic releases performed to avoid issues with notional approximations and for easier comparison with planned experiments Simulation of horizontal surface effects on horizontal subsonic hydrogen and methane jets were performed using Fluent :  Froude numbers values for the jets for a given leak orifice diameter of 6. mm, of : 50, 250, 500, 750 and  Variable distance between the centerline of the jet and the wall : 5cm, 20 cm and 50 cm Profiles of 50 % LFL contours of hydrogen free jets for various Froude numbers

12 Location Exp. values Swain et al. This work deviation (%) Average deviation 13.8 Cross validation of a simulation leak of hydrogen (D= 5 mm, 31.2 scfm, Fr=1000 ) by Houf et al. Inverse hydrogen mole fraction along jet centerline versus streamwise distance along jet centerline deviate from our simulation values using Fluent by an average deviation of 0. 8% Validation of experimental leak of hydrogen (D= mm, 22.9 slm, Fr=268) by Houf et al. Inverse hydrogen mole fraction along jet centerline versus streamwise distance along jet centerline deviate from our simulation values using Fluent by an average deviation of 5.17 % Swain et al. Fr=120 Validation simulations using Fluent (k-ε realizable) D=9.45 mm, v=134.5m/s D=1.905 mm, v=133.9 m/s

13 Hydrogen free jets Effects of buoyancy Methane free jets LFL contours of methane 5 cm from the ground20 cm from the ground50 cm from the groundFree jets LFL contours of hydrogen 5 cm from the ground20 cm from the ground50 cm from the groundFree jets Results

14 Effect of buoyancy on free jets Pitts

15 Surface effects on horizontal jets

16 Normalized relative extent

17 Lower Flammability extents  Hydrogen  Methane

18 Conclusions Vertical surfaces lead to a collapse of the curves of the flammable extent as a function of height when expressed as normalized relative extent when using isotropic turbulence models (both k- and Realizable) as reported earlier for vertical and zero g simulations ◦ True for both centreline and maximum flammable extent Crossover behaviour observed for maximum extent ◦ likely due to the proximity of the surface (law of the wall vs scaling behavior of the jet) Reversed behaviour for H2 and methane in the crossover region (NRE (Max extent) > NRE (Centerline)) which is not observed in 0 G simulations Similar collapse observed when the results are expressed as the NRE when performing subsonic simulations using Fluent and a different turbulence model

19 Conclusions Even if two different turbulent models concord qualitatively, the use of isotropic turbulence models (1) for jet and (2) close to a surface is a potential issue Comparison of LES simulations & experiments are needed before definitive conclusions

20 Acknowledgements Natural Resources Canada Natural Sciences and Engineering Council of Canada


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