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NIST neutron imaging facility for fuel cell imaging.

NIST neutron imaging facility for fuel cell imaging. National Institute of Standards and Technology Technology Administration U.S. Department of Commerce. Neutron Imaging. Fuel Cells. David Jacobson Daniel Hussey (NIST) Muhammad Arif (NIST). Jon Owejan (GM – FCA)

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NIST neutron imaging facility for fuel cell imaging.

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  1. NIST neutron imaging facility for fuel cell imaging. National Institute of Standards and Technology Technology Administration U.S. Department of Commerce Neutron Imaging Fuel Cells David Jacobson Daniel Hussey (NIST) Muhammad Arif (NIST) Jon Owejan (GM – FCA) Thomas Trabold (GM – FCA) Daniel Baker(GM – FCA) Satish Kandlikar (RIT)

  2. Support • DOE – Energy Efficiency and Renewable Energy • Nancy Garland Program Coordinator • DOC – NIST • NIST Directors office competence funding • NIST Intramural Advanced Technology Program • Gerald Caesar • NIST Physics Laboratory (www.physics.nist.gov) • NIST Center for Neutron Research (www.ncnr.nist.gov) • Patrick Gallagher (director), Charlie Glinka and many others who provide tremendous technical assistance.

  3. OLD NIST Neutron Imaging Facility • Intense neutron beam • Single or multi-stack cell • Variable beam diameter • Variable resolution

  4. LN Cooled Bismuth Filter 6 meter flight path Beam Stop Drum shutter and collimator 2.13 m Cable Ports Cable Ports Steel pellet and wax filled shield walls NEW Neutron Imaging Facility (NIF) • New facility 14.6 m2 (157 ft2) floor space • Accessible 2 meters to 6 meters • Variable L/d ratio • At 2 m L/d = 100 → ∞ • At 6 m L/d = 300 → ∞ • Maximum Intensity without filters • At 2 m = 1 x 109 n cm-2 sec-1 (L/d =100), 8 cm diameter beam size • At 6 m = 1 x 108 n cm-2 sec-1 (L/d =300), 25 cm diameter beam size • Maximum Intensity with 15 cm LN cooled Bismuth Filter • At 2 m = 2 x 108 n cm-2 sec-1 (L/d =100), 8 cm diameter beam size • At 6 m = 2 x 107 n cm-2 sec-1 (L/d =300), 25 cm diameter beam size • Support for fuel cell experiments • Hydrogen flow rates 18.8 lpm • 50 cm2 fuel cell controller with 5 lpm flow rates. • Nitrogen, Air, Coolant and Hydrogen Venting • Detection capabilities • Real-Time Varian Paxscan, 30 fps @ 0.254 mm pitch or 7.5 fps @ 0.127 mm pitch • Second Varian detector will upgrade to 30 fps @ 0.127 mm pitch • 2048 x 2048 Cooled (50° C) Andor CCD based box with 30 cm maximum field of view. • 2 more 1024 x 1024 Cooled (30° C) Apogee CCD based • Sample Manipulation • Motor controlled • 5 axis tomography capability • Phase imaging capable • Open for business January-March 2006

  5. NEW Neutron Imaging Facility (NIF) • New facility 14.6 m2 (157 ft2) floor space • Accessible 2 meters to 6 meters • Variable L/d ratio • At 2 m L/d = 100 → ∞ • At 6 m L/d = 300 → ∞ • Maximum Intensity without filters • At 2 m = 1 x 109 n cm-2 sec-1 (L/d =100), 8 cm diameter beam size • At 6 m = 1 x 108 n cm-2 sec-1 (L/d =300), 25 cm diameter beam size • Maximum Intensity with 15 cm LN cooled Bismuth Filter • At 2 m = 2 x 108 n cm-2 sec-1 (L/d =100), 8 cm diameter beam size • At 6 m = 2 x 107 n cm-2 sec-1 (L/d =300), 25 cm diameter beam size • Support for fuel cell experiments • Hydrogen flow rates 18.8 lpm • 50 cm2 fuel cell controller with 5 lpm flow rates. • Nitrogen, Air, Coolant and Hydrogen Venting • Detection capabilities • Real-Time Varian Paxscan, 30 fps @ 0.254 mm pitch or 7.5 fps @ 0.127 mm pitch • Second Varian detector will upgrade to 30 fps @ 0.127 mm pitch • 2048 x 2048 Cooled (50° C) Andor CCD based box with 30 cm maximum field of view. • 2 more 1024 x 1024 Cooled (30° C) Apogee CCD based • Sample Manipulation • Motor controlled • 5 axis tomography capability • Phase imaging capable • Open for business January-March 2006

  6. Hydrogen Safety • Computational Fluid Dynamics modeling • Free software • NIST Fire Dynamics Simulator (FDS) • http://www.fire.nist.gov/fds/ • Release point in reactor confinement building • Extremely high buoyancy turbulently mixes hydrogen resulting in low concentrations throughout room Hydrogen Plume 22 lpm

  7. Modeling Building Release Mass (kg/kg) x 10-4

  8. Modeling the Release Point Lower flammability limit Upper flammability limit Below 1 meter a maximum of 68 mg of hydrogen is expected to be within the range of 77% to 4% and so an unlikely detonation of such a mixture is expected to have an explosive yield similar to a few firecrackers.

  9. Converts neutrons to light 6LiF/ZnS:Cu,Al,Au Neutron scintillator CCD • Neutron absorption cross section for 6Li is huge (940 barns) 6Li + n0 4He + 3H + 4.8 MeV • Light is emitted in the green part of the spectrum Neutrons in Green light out • Neutron to light conversion efficiency is 20% Scintillator

  10. Real-Time Detector Technology • Amorphous silicon • Radiation hard • High frame rate (30 fps) • 127 micron spatial resolution • Picture is of water with He bubbling through it • No optics – scintillator directly couples to the sensor to optimize light input efficiency Helium through water at 30 fps Front view Scintillator aSi sensor Readout electronics Side view Neutron beam scintillator aSi sensor

  11. Hydrogen Fuel Cells

  12. 1 s exposure time 50 micron water thickness Water Sensitivity Wet cuvet Dry cuvet water only  = -ln = • Steps machined with 50 micron. • CCD camera exposure of 1 s yields a sensitivity of 0.005 g cm-2 s-1 • After 100 s a factor of 10 improvement gives 0.0005 g cm-2 s-1 • New amorphous silicon detector should have a least a factor of 7 improvement in temporal sensitivity

  13. Sensitivity required for fuel cells (assumes maximum water content) • Flow fields 0.020 g cm-2 • Gas diffusion media 0.012 g cm-2 • Electrode 0.0005 g cm-2 • Membrane 0.0005 g cm-2

  14. Single Cell Assembly Compression Plates Current Collectors Locating Pins Flow Fields Gaskets - GDM - MEA

  15. PEM Fuel Cell Operation 15 mm 15 mm 200 mm 25 mm 200 mm

  16. Flow rates of reactants • F : Farday constant 96484 Coulomb mol-1 • ideal : ideal molar gas density (1/22400) mol cm-3 • Stoich. Ratio • Definitions • J : Current density Amp cm-2 • A : Active area of cell • n : (mols electrons)/(mol reactant)

  17. H2 + ½ O2 H2O Fuel Cell Performance 1.2

  18. Fuel cell Neutron sensitive screen Point Source

  19. Orientation of Cell in all Images channel width = 1.4 mm; channel depth = 0.5 mm; land width = 1.5 mm Inlet Anode Inlet Cathode

  20. Orientation of Cell in all Images channel width = 1.4 mm; channel depth = 0.5 mm; land width = 1.5 mm Inlet Anode Inlet Cathode

  21. Amount of Water Possible Volume of one channel = 0.176 cm3 Volume of one port = 0.050 cm3 Volume of one flow field = 0.980 cm3 Volume of anode DM + cathode DM (70% porosity) + electrode (50% porosity) + membrane (20% uptake) = 1.160 cm3 Max water volume possible = 3.12 cm3

  22. Channel Geometries

  23. Channel Geometries explored • Rectangular channels • Water flow is laminar tending to constrict and plug the channels • Water plugs form as large slugs and can be difficult to remove. • Triangular channels • Water stays at the corner interface with the diffusion media leaving the apex of the channel more clear. • Water tends to come out in smaller droplets instead of large slugs, which require a high pressure differential to remove

  24. Flow Field Properties Gold Coated w/PTFE Contact Angle = 93° Gold Uncoated Contact Angle = 50° 1.37 mm 1.45 mm 0.38 mm Rectangular X-sect Xsect Area = 0.52 mm2 1.37 mm 1.45 mm 94° 0.76 mm Triangular X-sect Contact Resistance Values

  25. Test Parameters 100% Humidified 80°C 100kPag Approx. 150% exit RH 1 Hr 0.6V Start Up Gore 25mm 0.4/0.4 Toray 060/090 Teflon ground Cathode Flow Field Variation (Anode constant rect. x-sect no coating) 2 Channel Geometries Rectangular Triangular 2 Surface Energies Gold Gold coated ionic PTFE 4 Cathode FFs Total Rect and Tri (gold only) Rect and Tri (gold coated w/ ionic PTFE) Cathode Channel Cross Section Geometry and Surface Energy Study

  26. Rectangular Comparison 0.5 A/cm2 Uncoated PTFE Coated

  27. Triangular Comparison 0.5 A/cm2 Uncoated PTFE Coated

  28. Geometry Comparison 0.5 A/cm2 Uncoated Rectangular Uncoated Triangular

  29. Total Water Mass Tends

  30. Conclusions • Neutron imaging is an important and effective tool to study fuel cells in situ. • Computational fluid dynamics can be an extremely useful tool in analyzing safety of hydrogen gas released in a reactor hall. • Channel surface energy has a consistent effect on water slug shape and size. Higher contact angle increases average water mass retained, but distribution of smaller slugs more evenly in the channel area increases performance. • Triangular cross-sectional geometry accumulates water in the corners adjacent to diffusion media. The center of the channel does not become obstructed by stagnant slugs.

  31. Key Observations and Conclusions (cont’) Channel surface energy has a consistent effect on water slug shape and size. Higher contact angle increases average water mass retained, but distribution of smaller slugs more evenly in the channel area increases performance. • Triangular cross-sectional geometry accumulates water in the corners adjacent to diffusion media. The center of the channel does not become obstructed by stagnant slugs.

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