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  9/11/07   1        Sandia National Laboratories
Hydrogen Behavior – Myth Busting


                      Jay Keller,
            Sandia National Laboratories
                    Pierre Bénard,
        Université du Québec à Trois-Rivières

                    Topical Lecture
      The International Conference on Hydrogen
                        Safety

                September 11-13, 2007


                     9/11/07   2        Sandia National Laboratories
Acknowledgements

    The authors wish to recognize the following
    people for their contribution to the science
    discussed in this presentation.

    Groethe, Mark; SRI International
    Houf, Bill; Sandia National Laboratories
    Moen, Chris; Sandia National Laboratories
    Schefer, Bob; Sandia National Laboratories
    Andrei V. Tchouvelev; Tchouvelev & Associates




                        9/11/07   3     Sandia National Laboratories
Hydrogen Myths
 Hindenburg
    Hydrogen Caused the Disaster
 Hydrogen Molecular Diffusivity is 3.8 times that of CH4
    Therefore it diffuses rapidly and mitigates any hazard
 Hydrogen is 14.4 times lighter than air
    Therefore it rapidly moves upward and out of the way
 We do not know the flammability limits for H2




                                9/11/07   4        Sandia National Laboratories
Hydrogen Myths
 We just do not understand hydrogen combustion behavior
    Hydrogen release is different than other fuels
    Radiation is different than other fuels
 Hydrogen hazards can be compared favorably to
  experiences with other hydrocarbon fuels
    Less dangerous than gasoline, methane …
 Hydrogen is toxic and will cause environmental harm
    “… We need to be indemnified against a hazardous toxic hydrogen
     spill …” – Generic Insurance Company




                                9/11/07   5           Sandia National Laboratories
Hydrogen Myths
 Hindenburg
    Hydrogen Caused the Disaster
 Hydrogen Molecular Diffusivity is 3.8 times that of CH4
    Therefore it diffuses rapidly and mitigates any hazard
 Hydrogen is 14.4 times lighter than air
    Therefore it rapidly moves upward and out of the way
 We do not know the flammability limits for H2




                                9/11/07   6        Sandia National Laboratories
Lets get this out of the way!
Hindenburg Disaster
 36 out of 97 died mostly
  trapped by the fire of
  fabric, diesel fuel, chairs,
  tables … (not hydrogen)
 The craft did not explode
  but burned – and while
  burning stayed aloft
  (Hydrogen was still in the
  nose)
 The craft fell to the
  ground tail first – the nose
  was still full of hydrogen
 Radiation from the flame was red, orange
  and yellow – hydrogen flames emit in the
  near UV ~304 to 350 nm (OH* lines), 680 nm
  to 850 nm (vibrationally excited H2O), and
  ~0.5 to 23 mm (water bands)
                              9/11/07   7      Sandia National Laboratories
Lets get this out of the way!
Hindenburg Disaster (Cont’d)
 The covering was coated with cellulose nitrate
  or cellulose acetate -- both flammable
  materials. Furthermore, the cellulose material
  was impregnated with aluminum flakes to
  reflect sunlight. -- Dr. Addison Bain

 A similar fire took place when an airship with
  an acetate-aluminum skin burned in Georgia
               – it was full of helium!

 “I guess the moral of the story is, don’t paint
  your airship with rocket fuel.”
  -- Dr. Addison Bain

         Courtesy of Dr. Addison Bain and the National
         Hydrogen Association
                                      9/11/07   8        Sandia National Laboratories
Hydrogen Myths
 Hindenburg
    Hydrogen Caused the Disaster
 Hydrogen Molecular Diffusivity is 3.8 times that of CH4
    Therefore it diffuses rapidly and mitigates any hazard
 Hydrogen is 14.4 times lighter than air
    Therefore it rapidly moves upward and out of the way
 We do not know the flammability limits for H2




                                9/11/07   9        Sandia National Laboratories
Small Unignited Releases: Momentum-
Dominated Regime
                    Data for round turbulent jets
                                                                                1/Xcl_CL Decay_all.qpam
         25.0
                      He (Pitts,1 991)
                      CH4 (Pitts,199 1)
                      C3H8 (Pitts,19 91)
                      CH4 (Present study)
                      H2 (Present study)
                                                                                                           In momentum-dominated
         20.0
                                                                                                            regime, the centerline
                                                                                                            decay rate follows a 1/x
         15.0
                                                                                                            dependence for all gases.
                                                              CH
                                                                                                           The centerline decay rate
    cl




                                                               4
 1 /X




                                         C H
                                           3   8                                                            for mole fraction
         10.0
                                                                                                            increases with increasing
                                                                                                            gas density.
          5.0
                                                   He
                                                                          H
                                                                            2                              The decay rate for H2 is
                                                                                                            significantly slower than
                                                                                                            methane and propane.
          0.0
                0        20              40             60         80         100             120


                                                        X/d
                                                        z/d


                                                                        9/11/07              10               Sandia National Laboratories
Buoyancy effects are characterized by
Froude number
          Horizontal H2 Jet (dj=1.9 mm)
Fr=99
 Fr=99
Fr=99                                                                    Time-averaged H2 mole
                                                                          fraction distributions.
                                                                         Froude number is a
                                                                          measure of strength of
                                                  0.8
Fr=152                                                                    momentum force




                                                        Mole Fraction
Fr=152
 Fr=152                                                                   relative to the buoyant
                                                  0.6
                                                                          force
                                                  0.4                    Increased upward jet
                                                                          curvature is due to
                                                                          increased importance
Fr=268                                            0.2
Fr=268                                                                    of buoyancy at lower
Fr=268                                                                    Froude numbers.




                                   9/11/07   11                         Sandia National Laboratories
Influence of buoyant force is quantified
by the dimensionless Froude number
  Jets from choked flows (Mach 1.0) are                                                                                     Simulation of H2 Leak
                                                                                                                                Frden = 1000
   typically momentum-dominated.
  Lower source pressures or very large
                                                                                                        Y/D


   pressure losses through cracks lead to                                                                                                                     g

   subsonic, buoyancy-dominated plumes.                                                                       0.08 m.f.
                                                                                                                 0.07 m.f.
       Densimetric Froude Number for
         6
           Various Diameter Leaks
            10
                                 Mach No. = 1.0
            105                        Mach No. = 0.5
                                                                        Momentum
                                               Mach No. = 0.25                                                                                      X/D
                                                                        Dominated                                            Simulation of H2 Leak
                                                 Mach No. = 0.10
            104                                                                                                                  Frden = 100
    de n




           1000                                                                                        Y/D                                                   g
  F




           100                                                          Transition

            10
                     Mach No. = 0.01
                       Mach No. = 0.001
                                                                        Buoyancy
             1                                                          Dominated
             0.001        0.01           0.1            1          10
                                  Dia (mm)

 Frden = Uexit /(gD(ramb- rexit)/rexit)1/2                                                                                                         X/D
                                                                                                    Ricou and Spalding entrainment law (J. Fluid Mechanics, 11, 1961)
                                                                                     9/11/07   12                 Sandia National Laboratories
Small Unignited Releases: Buoyancy Effects
   Data for round H2 Jets (dj=1.91 mm)
                                                 1/Xcl_H2 & Pitts.qpam
       50
                 Re=2384,Fr=26 8
                 Re=1353,Fr=15 2
                 Re=884,Fr=99
                 Re=520,Fr=58
                 H2 (Houf)
                                                                          At the highest Fr, 1/XCL
       40        CH4 (Pitts)
                                                                           increases linearly with
                                                                           axial distance, indicating
                                                                           momentum dominates.
       30
                                                                          As Fr is reduced
  CL




                          Increasing Fr                                    buoyancy forces become
1/X




       20
                                                                           increasingly important
                                                                           and the centerline decay
                                                                           rate increases.
       10
                CH                                                        The transition to
                  4
                                                                           buoyancy-dominated
                                                                           regime moves upstream
        0
            0    20      40        60     80   100         120             with decreasing Fr.
                                    x/d

                                               9/11/07           13          Sandia National Laboratories
Hydrogen Myths
 Hindenburg
    Hydrogen Caused the Disaster
 Hydrogen Molecular Diffusivity is 3.8 times that of CH4
    Therefore it diffuses rapidly and mitigates any hazard
 Hydrogen is 14.4 times lighter than air
    Therefore it rapidly moves upward and out of the way
 We do not know the flammability limits for H2




                                9/11/07   14       Sandia National Laboratories
Choked & Unchoked Flows at 20 SCFM
Tank Pressure = 3000 psig, Hole Dia. = 0.297 mm
                                                                                     Correlations based on experimental data
Exit Mach Number = 1.0 (Choked Flow)
                                           H2 Mole Fraction                          Start Intermediate Region
Fr ~ O(104)
   0.2                                                                                     x/D = 0.5 F1/2(rexit/ramb)1/4
                                                                                     End Intermediate Region
R(m)




       0                                                                                   x/D = 5.0 F1/2(rexit/ramb)1/4
                                                                                     F = Exit Froude No.
 - 0.2                                                                                  = U2exit rexit/(gD(ramb- rexit))
           0               0.5    X(m)          1.0                  1.5

                                                                                         Start Transition Region -> x = 6.3 m
       Flowrate = 20 scfm, Hole Dia. = 9.44 mm
       Exit Mach Number = 0.1 (Unchoked Flow)
       Fr ~ O(100)
                                                                                     Assuming gases at 1 Atm, 294K
                                                                                      (NTP)
                                                                                            Red – 10.4%
                                         Start of                                           Orange – 8.5%
                                         Transition                                         Green – 5.1%
                                         Region (x = 0.3 m)
                                                                                            Blue – 2.6%

                                                      H2 Concentration Data from:                                   *(Chen and Rodi, 1980)
                                                      Dr. Michael Swain
       0       0.5   1.0    1.5   2.0    X(m)
                                                      Fuel Cell Summit Meeting
                                                      June 17, 2004
                                                                       9/11/07      15               Sandia National Laboratories
Hydrogen Myths
 Hindenburg
    Hydrogen Caused the Disaster
 Hydrogen Molecular Diffusivity is 3.8 times that of CH4
    Therefore it diffuses rapidly and mitigates any hazard
 Hydrogen is 14.4 times lighter than air
    Therefore it rapidly moves upward and out of the way
 We do not know the flammability limits for H2




                                9/11/07   16       Sandia National Laboratories
Flammability Limits for H2
                    Upward Flame Propagation

 Tube Dimensions,     Firing         Limits, percent        Water Vapor        Re ference
 cm                   end                                   Content
 Diame ter Length                Lower     Higher
    7.5      150      Close d     4.15      75.0     Half-saturated       356
    5.3      150      Ope n       4.19      74.0     Drie d                94
    5.3      150        Ņ         4.12         Horizontal Flame Propagation
                                            74.2        Ņ                  94
    5.3      150        Ņ         4.17      74.8        Ņ                  94
    5.0      150      Close d     4.15      74.5     Half-saturated       356
                          Tube Dimensions,      Firing      Limits, percent              Water Vapor      Re ference
    5.0      150          n
                      Opecm       4.00      72.0end Drie d                133            Content
    4.8      150        Ņ Diameter Length 73.8
                                  4.00                  Ņ Lower            38
                                                                      Higher
    4.5       80      Close d     4.10      -----       Ņ                  56
                             7.5       150      Close d     6.5        -----              Half-saturated       356
    4.5       80        Ņ    5.0  3.90 150 ----- Ņ      Ņ 6.7              57
                                                                       -----                     Ņ             356
                               2.5         150        Ņ             7.15       Propagation in a Spherical Ves
                                                                                 -----           Ņ             356
                               2.5         150      Ope n            6.2         -----    Saturate d           271
  Downward Flame Propagation   2.5         -----      Ņ                 Capacity, cc
                                                                     -----       71.4     Firing
                                                                                          -------     Limits, percent
                                                                                                               273       Water Vap
                               0.9         150        Ņ              6.7         65.7     end
                                                                                          Saturate d Lower      Higher
                                                                                                               276       Content
                                                                        Not stated        Closed      9.2         ----   Saturated
   Tube Dimensions,      Firing         Limits, percent          Water Not stated Reference
                                                                         Vapor               Ņ        8.5        67.5      Ņ
   cm                    end                                     Content1,000                Ņ        8.7        75.5      Ņ
   Diameter Length                    Lower        Higher               810                  Ņ        5.0        73.5      Ņ
     21.0      31        Open          9.3           ----        Saturated
                                                                        350            63 Ņ           4.6        70.3      Ņ
      8.0      37        Closed        8.9          68.8         Half-saturated
                                                                        35             324 Ņ          9.4        64.8      Ņ
      7.5      150         Ņ           8.8          74.5         Ņ                     356
      7.0      150         Ņ           -----        74.5         Saturated             115
      6.2      33        Open          8.5           ----        Partly dried          95
      6.0      120         Ņ           9.45          ----        Ņ                     325
                                                       9/11/07        17                Sandia National Laboratories
Flammability Limits for H2
                    Upward Flame Propagation

 Tube Dimensions,     Firing         Limits, percent        Water Vapor        Re ference
 cm                   end                                   Content
 Diame ter Length                Lower     Higher
    7.5      150      Close d     4.15      75.0     Half-saturated       356
    5.3      150      Ope n       4.19      74.0     Drie d                94
 78 investigations of hydrogen flammability
    5.3
    5.3
             150
             150
                    Horizontal Flame Propagation
                        Ņ
                        Ņ
                                  4.12
                                  4.17
                                            74.2
                                            74.8
                                                        Ņ
                                                        Ņ
                                                                           94
                                                                           94
    5.0      150      Close d     4.15      74.5     Half-saturated       356
  limits were identified between 1920 Vapor 1950.
    5.0      150
                          Tube Dimensions,
                      Opecm
                          n       4.00
                                           Water
                                            72.0 and Re ference
                                                Firing
                                                end Drie d
                                           Content
                                                            Limits, percent
                                                                          133
    4.8      150        Ņ Diameter Length 73.8
                                  4.00                  Ņ Lower            38
                                                                      Higher
 Hydrogen flammability limits areHalf-saturated 356
    4.5
    4.5
              80
              80
                      Close d
                        Ņ
                             7.5
                             5.0
                                  4.10
                                       150  well
                                            -----
                                                Close d
                                  3.90 150 ----- Ņ
                                               Ņ
                                                        Ņ
                                                        Ņ 6.7
                                                         356
                                                            6.5
                                                                           56
                                                                       -----
                                                                           57
                                                                       -----
                                    Propagation in a Spherical Ves
  established.2.5
              2.5
                  150
                  150
                         Ņ
                       Ope n
                               7.15
                               6.2
                                     -----
                                     -----
                                               Ņ
                                           Saturate d
                                                         356
                                                         271
  Downward Flame Propagation
               2.5   ----- Ņ                                            Capacity, cc
                                                                     -----       71.4    Firing
                                                                                         -------     Limits, percent
                                                                                                              273       Water Vap
                               0.9         150          Ņ            6.7         65.7    end
                                                                                         Saturate d Lower      Higher
                                                                                                              276       Content
                                                                        Not stated       Closed      9.2         ----   Saturated
   Tube Dimensions,      Firing         Limits, percent          Water Not stated Reference
                                                                         Vapor              Ņ        8.5        67.5      Ņ
   cm                    end                                     Content1,000               Ņ        8.7        75.5      Ņ
   Diameter Length                    Lower      Higher                 810                 Ņ        5.0        73.5      Ņ
     21.0      31        Open          9.3         ----          Saturated
                                                                        350           63 Ņ           4.6        70.3      Ņ
      8.0      37        Closed        8.9        68.8           Half-saturated
                                                                        35            324 Ņ          9.4        64.8      Ņ
      7.5      150         Ņ           8.8        74.5           Ņ                    356
      7.0      150         Ņ           -----      74.5           Saturated            115
      6.2      33        Open          8.5         ----          Partly dried         95
      6.0      120         Ņ           9.45        ----          Ņ                    325
                                                       9/11/07        18               Sandia National Laboratories
What is a Reasonable Flame
Stabilization Limit?
                                                                                                Volume
                                                                                                Fraction


                                                      unignited jet footprint




 Which volume fraction contour is relevant:
    lean flammability limit? … 4% or 8%
    detonation limit? … 18%
    a fraction of the lowest lean flammability limit?
     … 1%
 Ignition of hydrogen in turbulent jets
  occurs around 8% as measured by
  Swain.
    This is consistent with the downward
     propagating limit of 8%

                                            9/11/07      19              Sandia National Laboratories
Hydrogen Myths
 We just do not understand hydrogen combustion behavior
    Hydrogen release is different than other fuels
    Radiation is different than other fuels
 “Hydrogen hazards can be compared favorably to
  experiences with other hydrocarbon fuels
    Less dangerous than gasoline, methane …
 Hydrogen is toxic and will cause environmental harm
    “… We need to be indemnified against a hazardous toxic hydrogen
     spill …” – Generic Insurance Company




                                9/11/07   20          Sandia National Laboratories
Hydrogen jets and flames are similar to
other flammable gases
                          Xr_vs _tau_ all_04/23/04.qpaf
                    0.3
                                      CO/H2

                                                                                                                                            Fraction of chemical energy
                                      CH4
                   0.25               C3H8
                                      C2H4
                                      Present Data
                                      CH4 (d=1.91 mm)                                                                                       Converted to thermal radiation
Radiant Fraction




                    0.2               H2 (d=1.91 mm)
                                      H2 (d=7.94 mm)
                   0.15
                                      H2    "
                                                                                                                                            Radiation heat flux distribution
                    0.1                                                                                                                     Jet length
                   0.05                                                                                                                                                                                                       l
                                                                                                                                                                                                                   L* _vs_Fr_A l _04/ 27/ 05. qpaf3
                                                                                                                                                     10 2


                     0
                          1                                    10                                100                                1000

                                                           Flame residence Time (ms) (kW)
                                           C* _vs_x/Lvis_all.q pa2
                                                                               Fuel S
                                                                                                                                                                          2/ 5
                                                                                                                                                                  L*=13.5Fr /(1+0.07Fr
                                                                                                                                                                                         2
                                                                                                                                                                                             )
                                                                                                                                                                                                 1/ 5

                               1.2                                                                                                                                                                                          L*=23
                                                                                               C2H4 11.2
                                                                                               C2H4 20.2
                                                                                               CH4 12.5
                               1.0                                                             CH4          6.4
                                                                                               C2H2 18.1
                                                                                               C2H2 56.5




                                                                                                                                                L*
                                                                                               Fit to data                                           10
                              0.80                                                              La rge -S cale H2 data:
                                                                                    Da ta FromPre se nt H2 Te sts
                                                                                    Listed Be low :
                                                                                               d=1.905 mm
                                                                                               d=7.938 mm (5 se c)                                                                                      H2 choked (d=7 .94 mm)
                    C*




                              0.60                                                             (1 0se c)
                                                                                               (2 0se c)                                                                                                H2 unchoked (d =7.94 mm)
                                                                                               (5 se c)                                                                                                 H2 choked (d=5 .08 mm)
                                                                                               (1 0se c)                                                                                                H2 (d=1.91 mm)
                              0.40                                                             (2 0se c)                                                                                                CH4 (d=1.91 mm))
                                                                                                                                                                                                        CH4 (Kalghatgh i)
                                                                                                                                                                                                        C3H8 (Kalghatg hi)
                              0.20                                                                                                                                                                      H2 (Kalghatghi)
                                                                                                                                                                                                        Buoyant regime (d=1.91 mm)
                                                                                                                                                     1.0
                               0.0                                                                                                                          0.1                  1.0                        10.0                             100.0
                                     0.0          0.50               1.0    1.5            2.0          2.5          3.0

                                                                           x/L                                                                                                                    Fr
                                                                                 v is
                                                                                                                          9/11/07          21                          Sandia National Laboratories
H2 Flame Radiation
                                         0.15


                                                    OH

                                                                                        H O
                                                                                                                            Orange emission
 Emission (arb. units)




                                                                                         2
                                         0.10


                                                                 Blue
                                                                 Continuim
                                                                                                                             due to excited
                                         0.05
                                                                                                                             H2O vapor
                                                                                                                            Blue continuum
                                         0.00
                                                0         200        400         600         800         1000                due to emission
                                                                     Wavlength (nm)
                                                                                                                             from OH + H =>
                                            8        OH


                                                                       H O
                                                                                                                             H2O + hn
                                                                           2
                 Emission (arb. units)




                                                                                                                            UV emission due
                                            6




                                            4
                                                                                                                             to OH*
                                            2
                                                                                                                            IR emission due
                                            0
                                                0         2000      4000         6000        8000        10000
                                                                                                                             to H2O vibration-
                                                                     Wavelength (nm)
                                                                                                                             rotation bands
 H2O emission in IR accounts
 for 99.6% of flame radiation
                                                                                                    9/11/07      22   Sandia National Laboratories
Hydrogen jets and flames are similar to
other flammable gases
                          Xr_vs _tau_ all_04/23/04.qpaf
                    0.3
                                      CO/H2

                                                                                                                                            Fraction of chemical energy
                                      CH4
                   0.25               C3H8
                                      C2H4
                                      Present Data
                                      CH4 (d=1.91 mm)                                                                                       Converted to thermal radiation
Radiant Fraction




                    0.2               H2 (d=1.91 mm)
                                      H2 (d=7.94 mm)
                   0.15
                                      H2    "
                                                                                                                                            Radiation heat flux distribution
                    0.1                                                                                                                     Jet length
                   0.05                                                                                                                                                                                                       l
                                                                                                                                                                                                                   L* _vs_Fr_A l _04/ 27/ 05. qpaf3
                                                                                                                                                     10 2


                     0
                          1                                    10                                100                                1000

                                                           Flame residence Time (ms) (kW)
                                           C* _vs_x/Lvis_all.q pa2
                                                                               Fuel S
                                                                                                                                                                          2/ 5
                                                                                                                                                                  L*=13.5Fr /(1+0.07Fr
                                                                                                                                                                                         2
                                                                                                                                                                                             )
                                                                                                                                                                                                 1/ 5

                               1.2                                                                                                                                                                                          L*=23
                                                                                               C2H4 11.2
                                                                                               C2H4 20.2
                                                                                               CH4 12.5
                               1.0                                                             CH4          6.4
                                                                                               C2H2 18.1
                                                                                               C2H2 56.5




                                                                                                                                                L*
                                                                                               Fit to data                                           10
                              0.80                                                              La rge -S cale H2 data:
                                                                                    Da ta FromPre se nt H2 Te sts
                                                                                    Listed Be low :
                                                                                               d=1.905 mm
                                                                                               d=7.938 mm (5 se c)                                                                                      H2 choked (d=7 .94 mm)
                    C*




                              0.60                                                             (1 0se c)
                                                                                               (2 0se c)                                                                                                H2 unchoked (d =7.94 mm)
                                                                                               (5 se c)                                                                                                 H2 choked (d=5 .08 mm)
                                                                                               (1 0se c)                                                                                                H2 (d=1.91 mm)
                              0.40                                                             (2 0se c)                                                                                                CH4 (d=1.91 mm))
                                                                                                                                                                                                        CH4 (Kalghatgh i)
                                                                                                                                                                                                        C3H8 (Kalghatg hi)
                              0.20                                                                                                                                                                      H2 (Kalghatghi)
                                                                                                                                                                                                        Buoyant regime (d=1.91 mm)
                                                                                                                                                     1.0
                               0.0                                                                                                                          0.1                  1.0                        10.0                             100.0
                                     0.0          0.50               1.0    1.5            2.0          2.5          3.0

                                                                           x/L                                                                                                                    Fr
                                                                                 v is
                                                                                                                          9/11/07          23                          Sandia National Laboratories
Thermal Radiation from Hydrogen
Flames
                    0.2
                              H2 lab
                                                              Alej andro_ Fig.1,qpa
                                                                                                    Previous radiation data for
                              H2 T#1
                              H2 T#2                                                                 nonsooting CO/H2 and CH4 flames
                              H2 T#3

                   0.15
                              CH4 Turns & Myhr
                              CH4 lab                                                                correlate well with flame
                              CO/H2 Turns & Myh r
                                                                                                     residence time.
Radiant Fraction




                    0.1
                                                                                                    Sandia’s H2 flame data is a factor
                                                                                                     of two lower than the
                                                                                                     hydrocarbon flame data.
                   0.05
                                                                                                                                                                      Alej andro_ Fig.2.qpa
                                                                                                                       0.2
                                                                                                                                Xr:H2 lab
                                                                                                                                Xr:H2 T#1
                                                                                                                                Xr:H2 T#2
                     0                                                                                                          Xr:H2 T#3
                          1             10              100                           1000                                      Xr:CH4 T&M
                                                                                                                      0.15      CH4 lab
                                        Residence Time (ms)                                                                     Xr:CO/H2 T&M




                                                                                                   Radiant Fraction
           Radiation heat flux data collapses
            on singe line when plotted against                                                                         0.1


            product G x ap x Tf4 .
           ap (absorption coefficient) is                                                                            0.05

            factor with most significant
            impact on data normalization                                                                                0
                                                                                                                         1013            1014                  1015                           1016
           Plank mean absorption coefficient for
                                                                                                                                       g x ap x (T f) 4 (ms m -1 K4 )
            different gases must be considered

                                                                                         9/11/07             24                    Sandia National Laboratories
Hydrogen Myths
 We just do not understand hydrogen combustion behavior
    Hydrogen release is different than other fuels
    Radiation is different than other fuels
 “Hydrogen hazards can be compared favorably to
  experiences with other hydrocarbon fuels
    Less dangerous than gasoline, methane …
 Hydrogen is toxic and will cause environmental harm
    “… We need to be indemnified against a hazardous toxic hydrogen
     spill …” – Generic Insurance Company




                                9/11/07   25          Sandia National Laboratories
Comparisons of NG and H2 Behaviors
                                                                                         Assume 3.175 mm (1/8 inch) dia. hole
                              Comparison of Blow-Off Velocities
                                for Hydrogen and Natural Gas
                                                                                         Unignited jet lower flammability limits
                   8000
                                                                 ubo_vs_dj .qpa2
                                                                                                   LFL H2 - 4% mole fraction
                                                                                                   LFL NG - 5% mole fraction
                   7000

                                                                                         Flame blow-off velocities for H2 are
                   6000
                                     Hydrogen Gas                                         much greater than NG
Velocity (m/sec)




                   5000                                                                  Flow through 1/8” diameter hole is
                   4000
                                                                                          choked
                                                                                                   Vsonic = 450 m/sec for NG (300K)
                   3000
                                        H2 Sonic Velocity                                          Vsonic = 1320 m/sec for H2 (300K)
                   2000
                                        NG Sonic Velocity
                                                                                         Hole exit (sonic) velocity for NG is
                   1000
                                                  Methane Gas                             greater than NG blow-off velocity
                                                                                                   No NG jet flame for 1/8” hole
                                                                                         Hole exit (sonic) velocity for H2 is much
                      0
                          0     10     20    30     40      50   60      70        80


                                            Jet Diameter (mm)
                                                                                          less than blow-off velocity for H2
                                                                                                   H2 jet flame present for 1/8” hole
                                3.175 mm (1/8 inch) diameter hole
                                                                                        9/11/07       26          Sandia National Laboratories
  Small Unignited Releases: Momentum-
  Dominated Regime
                                                                 1/ Xcl&1/ Ycl_vs_z /d. qp a4

                                                                                XCH4
                 1                                                              XH2




                0.8
Mole Fraction




                0.6                                                                              Decay rate for H2 mole
                                                                                                  fraction is slower than
                0.4
                                                                                                  CH4.
                                         X
                                             H2


                               X
                0.2                CH4




                 0
                      0   20   40                 60                 80                  100

                                         x/d




                                                       9/11/07             27                    Sandia National Laboratories
Unignited jet concentration decay
distances for natural gas and hydrogen.

                         Distance on Jet Centerline to Lower Flammability Limit
                                     for Natural Gas and Hydrogen

 Tank Pressure              Hole Diameter            Distance to 5% Mole    Distance to 4% Mole Fraction.
                                                     Fraction Natural Gas   Hydrogen
 18.25 bar (250 psig)       3.175 mm (1/8 inch)       1.19 m (3.90 ft)      4.24 m (13.91 ft)
                           1.587 mm (1/16 inch)      0.59 m (1.93 ft)       2.12 m ( 6.95 ft)

 207.8 bar (3000 psig)     3.175 mm (1/8 inch)       3.92 m (12.86 ft)      13.54 m (44.42 ft)
                           1.587 mm (1/16 inch)     1.96 m ( 6.43 ft)        6.77 m (22.21 ft)




    Distance to the lower flammability limit for hydrogen
    is about 3 times longer than for natural gas

                                                  9/11/07     28            Sandia National Laboratories
 Effects of surfaces ?
While both
 flammable
 envelopes lengths
 are increased, the
                     H2
 increase is more
 pronounced for CH4
 jets than H2 jets
“Transient puffs”
 seems to lead to a
 larger temporary
 increase of extent CH4
 of horizontal H2
 surface jets
                          9/11/07   29   Sandia National Laboratories
Small Unignited Releases:
Ignitable Gas Envelope
 H2 Jet at Re=2,384; Fr = 268   CH4 Jet at Re=6,813; Fr = 478




                                                                                 H2 flammability
                                                          0.8
                                                                                  limits: LFL
                                                                                  4.0%; RFR 75%
                                                                                 CH4
                                                                                  flammability




                                                                Mole Fraction
                                                          0.6
                                                                                  limits: LFL
                                                                                  5.2%; RFR 15%
                                                          0.4




                                                          0.2


                                                                                Radial profiles in H2 jet, d =
                                                                                1.91 mm, Re = 2384




                                      9/11/07   30          Sandia National Laboratories
 Is there a myth about the
 minimum ignition energy?
Lower ignition
 energy of H2 is
 the lowest of
 the flammable
 gases at
 stoichiometry
   Over the
    flammable
    range of CH4
    (below 10%),
    however, H2 has
    a comparable
    ignition energy.


                       9/11/07   31   Sandia National Laboratories
Hydrogen Myths
 We just do not understand hydrogen combustion behavior
    Hydrogen release is different than other fuels
    Radiation is different than other fuels
 “Hydrogen hazards can be compared favorably to
  experiences with other hydrocarbon fuels
    Less dangerous than gasoline, methane …
 Hydrogen is toxic and will cause environmental harm
    “… We need to be indemnified against a hazardous toxic hydrogen
     spill …” – Generic Insurance Company




                                9/11/07   32          Sandia National Laboratories
Some people just do not get it!
      H2
        is not toxic,
        it is environmentally benign
        We just borrow it -- (2H20 + E -> 2H2 + O2; then
         2H2+O2 -> 2H2O + E)
      H2 is a fuel and as such has stored
       chemical energy
        It has hazards associated with it
            • It is no more dangerous than the other fuels that
              store chemical energy
            • IT IS JUST different; -- WE UNDERSTAND THE
             SCIENCE

   We will learn how to safely handle H2 in the
   commercial setting just as we have for our
   hydrocarbon fuels.
                          9/11/07   33    Sandia National Laboratories
Publication list
                                              (1)     Houf and Schefer, “Predicting Radiative Heat Fluxes and Flammability Envelopes from Unintended Releases
                                                     of Hydrogen,” accepted for publication Int. Jour. of Hydrogen Energy, Feb. 2006.
                                              (2)     Schefer, Houf, San Marchi, Chernicoff, and Englom, “Characterization of Leaks from Compressed Hydrogen
                                                     Dispensing Systems and Related Components,” Int. Jour. of Hydrogen Energy, Vol. 31, Aug. 2006.
                                              (3)     Molina, Schefer, and Houf, “Radiative Fraction and Optical Thickness in Large-Scale Hydrogen Jet Flames,”
                                                     Proceedings of the Combustion Institute, April, 2006.
                                              (4)     Houf and Schefer, “Rad. Heat Flux & Flam. Env. Pred. from Unintended Rel. of H2,” Proc. 13th
                                                     Int. Heat Tran. Conf., Aug., 2006.
                                              (5)     Schefer, Houf, Williams, Bourne, and Colton, “Characterization of High-Pressure, Under-Expanded Hydrogen-Jet
                                                      Flames,” submitted to Int. Jour. of Hydrogen Energy, 2006.
                                              (6)     Houf and Schefer, “Predicting Radiative Heat Fluxes and Flammability Envelopes from Unintended Releases of
                                                      Hydrogen,” 16th NHA Meeting, Washington, DC, March 2005.
                                    11.3 m
                                              (6)     Schefer, R. W., Houf, W. G., Bourne, B. and Colton, J., “Turbulent Hydrogen-Jet Flame Characterization”, Int. Jour. of
                                                      Hydrogen Energy, 2005.
                                              (7)     Schefer, R. W., Houf, W. G., Bourne, B. and Colton, J., “Experimental Measurements to Characterize the Thermal and
                                                      Radiation Properties of an Open-flame Hydrogen Plume”, 15th NHA Meeting, April 26-30, 2004, Los Angeles, CA.
                                              (8)     Schefer R. W., “Combustion Basics,” in National Fire Protection Association (NFPA) Guide to Gas Safety, 2004.
                                              (9)     P. Bénard (2007), Chapter 3 – Hydrogen Release and Dispersion - Release of hydrogen - section a.1, , Biennial Report
                                                      on Hydrogen Safety, HySafe.
                                              (10)    B. Angers, A. Hourri, P. Bénard, P. Tessier and J. Perrin (2005), “Simulations of Hydrogen Releases from a Storage
                                                      Tank: Dispersion and Consequences of Ignition”. International Conference on Safety 2005, Sept 8-10, 2005, Pisa, Italy.
                                              (11)    A.V. Tchouvelev, P. Bénard, V. Agranat and Z. Cheng (2005), “Determination of Clearance Distances for Venting of
                                                      Hydrogen Storage”. International Conference on Safety 2005, Sept 8-10, 2005, Pisa, Italy (NRCAN, AUTO 21).
                                              (12)    Tchouvelev A., P. Bénard, D. R. Hay, V. Mustafa, A. Hourri, Z. Cheng, Matthew P. Large, Quantitative Risk
Nighttime photograph of ~40 MPa                       Comparison of Hydrogen and CNG Refuelling Options, Final Technical Report to Natural Resources Canada for the
large-scale H2 jet-flame test (dj = 5.08mm,           Codes and Standards Workshop of the CTFCA, August 2006 (194 pages).
                                              (13)    Bénard, P., Tchouvelev, A., Hourri, A., Chen, Z., Angers, B. High Pressure Hydrogen Jets in a Presence of a Surface.
Lvis = 10.6 m) from Sandia/SRI tests.                 Proceedings of International Conference on Hydrogen Safety, San Sebastian, Spain, September 2007.
                                              (14)    Tchouvelev, A.V., Howard, G.W. and Agranat, V.M. Comparison of Standards Requirements with CFD Simulations
                                                      for Determining of Sizes of Hazardous Locations in Hydrogen Energy Station. Proceedings of the 15th World
                                                      Hydrogen Energy Conference, Yokohama, June 2004.




                                                               9/11/07            34                        Sandia National Laboratories
Presentation End




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