1. Optical Diagnostics and Modeling of Different Reacting and Non-reacting Systems Saptarshi Basu Mechanical Engineering Department University of Connecticut

2. Ph.D Research Projects Soot topography in diffusion flames wrapped by line vortex Scalar mixing in vortex Innovative laser based non-intrusive diagnostics in fuel cells

3. Ph.D Research Projects Hydrodynamics and heat transfer in liquid films over rotating disk Plasma synthesis of ceramics

4. Publications Fuel Cell Diagnostics [Experimental] 1.Basu, S., Xu, H., Renfro, M. W., and Cetegen, B. M. (2004). ASME Journal of Fuel Cell Science and Technology, Vol 3 February 2006 2.Basu, S., H. Gorgun, Renfro, M. W., and Cetegen, B. M. (2005). Journal of Power Sources, 159 (2006) 3.Basu, S., Renfro, M. W., and Cetegen, B. M. Journal of Power Sources, 162 (2006) Patents S.Basu, M.W Renfro, B.M Cetegen, Fiber Optic based in-situ diagnostics for PEM fuel cells. Patent pending Vortex Dynamics [Modeling & Experimental] 4. Cetegen, B. M. and Basu, S. (2006). Combustion and Flame, 146(2006) 5. Basu, S., Barber, T and Cetegen, B. M. (2006), In Review Physics of fluids, July 2006

5. Publications Heat Transfer over Rotating Disk [Modeling] 6. Basu, S. and Cetegen, B. M. (2005). ASME Journal of Heat Transfer, Vol 128, March 2006 7. Basu, S. and Cetegen, B. M. (2005), In Press ASME Journal of Heat Transfer Plasma Synthesis of Ceramics [Modeling & Experimental] 8. Basu, S. and Cetegen, B. M. Accepted for publication in International Journal of Heat and Mass Transfer, July 2006 9. Basu, S., E.H Jordan and Cetegen, B. M., Invited paper in Journal of Thermal Spray Technology, January 2007 10. Basu, S. and Cetegen, B. M., submitted to Acta Materialia, January 2007

6. Modeling and Diagnostics of Solution Precursor Plasma Spray Process Funding Agency ONR Grant No. N00014-02-1-0171

7. Thermal Barrier Coating Padture et al, Science 2002 Gas Turbine Blades Temperature Reduction upto 300ºC

8. Solution Precursor Plasma Spray Process Precursor : Aq Soln. Zr + Yittria Salts => 7YSZ Alumina + YSZ

9. Important Parameters Affecting Coating Quality Initial Loading of Salts Droplet Size Plasma Temperature and Velocity Field Injection Velocity Type of Injection (Transverse or Co-axial) Precursor Property like 7YSZ or Alumina etc Standoff Distance All affects droplet level transport

10. Effect of Processing Hardness: 365 Density: 73 % Hardness: 760 Density: 82 % Hardness: 1020 Density: 95 % + Droplet level transport needs to be understood for process improvement This improvement takes years of trial and error

11. Modeling Axial Injection Entire thermal history of the droplets Mass transport at the droplet level in the plasma

12. Droplet Vaporization and Precipitation Routes (A)Volume precipitation (B)(I) fragmented shell formation (low permeability through the shell, (II) unfragmented shell formation (high permeability), (III) impermeable shell formation (C)Elastic shell formation, inflation and deflation

13. Predict precipitation (surface or volume) of droplets Model droplet level transport for better understanding of the role of process parameters on droplet morphology Predict shattering of shells after precipitation SEM image of the deposition on a substrate after a single pass. Cracked and dried Shell Motivation Xie et al 2003

14. High Relative Velocity Low Surface Tension Large Droplet Size Timescale of microsecs Timescale of millisecs Timescale of microsecs Three Stages of Droplet Modeling

15. Aerodynamic Breakup Aerodynamic breakup of 50 micron initial diameter 7YSZ droplets for a surface tension of 0.036 N/m

16. Aerodynamic Breakup (II) Not an issue for droplets of diameter less than 50 microns

17. Heating and Vaporization (2D) Models tried are 2D transient heat and species transport coupled with plasma Spherically symmetric heat and species transport Energy (2D) Species (2D)

18. Heating and Vaporization (1D) Energy (1D) Species (1D) Precipitation based on homonuclear hypothesis Precipitation triggered whenever solute concentration at surface reaches super saturation limit

19. Heating and Vaporization (2D) Computed droplet temperature (left) and solute mass fraction (right) for a 40 micron droplet injected into a DC arc plasma at 1 ms (top) and 3 ms (bottom)

20. Precipitation (2D) d = 5  m. d = 10  m. d = 20  m. Xie et al Mater. Sci. Eng A 2003 What is shell porosity What is the morphology/property of the shell

21. Internal Pressurization The model of the interior of the particle is divided into three zones Internal pressure buildup due to heating and lack of evaporation Porosity of the shell

22. Internal Pressurization 10 micron initial sized droplets Pressure rise decreases with porosity due to venting 40 micron initial sized droplets Pressure rise decreases with porosity due to venting

23. Conclusions Droplets below 50 micron do not undergo aerodynamic breakup Precipitation occurs when surface concentration of solute reaches supersaturation Small droplets < 5 microns tend to volume precipitate Large droplets surface precipitate forming thin shells Low porosity shells fracture on further heating in the plasma High porosity shells do not fracture and arrive at the substrate as unpyrolized material with watery core

24. Limitations No precipitation kinetics is modeled Literature show precipitation is not homonuclear No experimental data is available for precipitation at high heating rates Behavior of droplets in an array or vicinity of other droplets is not modeled

25. Future Research Direction Physical evolution of particulate formation in droplets at rapid heating rates 10 5 to 10 7 K/s. [FUNDING NSF : CBET/ONR : Collaboration AMPAC/UCONN] The morphology, microstructure and chemical composition of droplets evolution as a function of time [FUNDING NSF : CBET /ONR: Collaboration AMPAC/UCONN] Advanced modeling with improved precipitation mechanism [FUNDING NSF : CBET /ONR : Collaboration UCONN] Provide general guidelines for processing routes for different types of precursors for different microstructure for advanced applications In situ monitoring of splat dynamics and transient composition variation [FUNDING NSF : CBET /ONR]

26. Future Research Direction Laser heating of droplets Advantages Similar heating rates as in the plasma Similar timescales for precipitate formation Diagnostics are easier to carry out Similar profiles

27. Future Research Direction High speed imaging of precipitation Different kinds of precursors investigated Ex situ analysis of morphology of collected sample using SEM, FTIR and Raman

28. Future Research Direction High Temperature resistant Fiber Optic In situ analysis of splat by infrared fiber optic evanascent spectrsocopy Transient composition variation can be monitored

29. In-situ Simultaneous Measurements of Temperature and Partial Pressure in a PEM Fuel Cell under Steady and Dynamic cycles Funding Agency U. S. Army Research RDECOM

30. Presentation Outline l Development and calibration of diode laser based absorption measurement technique for water vapor concentration measurement l Application of the measurement technique to an operating fuel cell l Theoretical method to extract temperature and partial pressure simultaneously using a single laser scan l Experimental Results of partial pressure and temperature in a PEM fuel cell under steady conditions l Experimental Results of partial pressure and temperature in a PEM fuel cell under dynamic conditions l Extensions and improvements of the measurement technique to spatially resolved measurements l Concluding Remarks

31. Introduction to PEM fuel cells At the anode the hydrogen gas ionizes releasing electrons and protons (H +). 2H 2  4H + + 4e - This reaction releases energy. At the cathode, the oxygen reacts with electrons taken from the electrode, and H + from the electrolyte, to form water. O 2 + 4e - + 4H +  2H 2 O Bipolar plate contains the gas channels for circulating the air and hydrogen Courtesy : Dr. J. Fenton

32. Water management in PEM fuel cells Water diffusion from cathode to anode Water supplied by externally humidification Water removed by circulating hydrogen Water produced within the cathode Water transport due to electro-osmotic drag by protons The depleted air leaving the fuel cell remove water Water supplied by externally humidifying the air/O 2 supply Main Challenges Flooding/drying up of membrane Real time humidity level control in inflow gas streams

33. Proton flux through the membrane directly proportional to the current density in a MEA. Careful balancing of the supply and removal of water vapor to prevent FLOODING/ DRYING and BETTER PERFORMANCE and DURABILITY Protonic conductivity of several membrane materials as a function of relative humidity at T=100 ºC studied by Alberti et al Water management in PEM fuel cells

34. Water vapor measurements in fuel cells l Current state-of-the-art limited only to inlet and outlet measurements or expensive instrumentation l Fourier transform IR (FTIR) spectrometer l Gas chromatograph l Neutron Scattering l Most measurements performed at the INLET and OUTLET of the cell l Intrusive techniques require extraction of the sample from the fuel cell and sending it to the external measurement device Both techniques provide slow, temporally and spatially averaged measurements l There is a GREAT NEED to measure water vapor concentration non- intrusively with good spatial and temporal resolution

35. Water Management & Transport (DOE)

36. l Water Transport l Impurity sensor like CO sensor l Novel concepts l Cold start

37. Tunable Diode Laser Absorption Spectroscopy (TDLAS) l Non-intrusive, in-situ first of its kind of measurements l Line of sight absorption in individual flow channels l Measurement time: ~seconds l Off-the-shelf telecommunications cheap lasers (~$500) l Total system cost ~$5000 l Straightforward extension to other species such as CO, CO 2 l Ability to measure multiple channels or species simultaneously via multiplexing l Ability to measure temperature across each channel using a single laser scan l Potential use in feedback control systems l Potential use in high temperature fuel cells like SOFC l Potential use in Direct Methanol Fuel Cells

38. Beer-Lambert law Absorption of light by a sample = Transmitted light intensity = Incident light intensity = Partial pressure of water vapor = Absorption coefficient The measured partial pressure represents a path-averaged value Proper Selection of Wavelength is crucial

39. Simulated signal l Voigt profile simulation with HITRAN database parameters

40. Test cell for system calibration l Simple humidity and temperature controlled absorption cell constructed for system calibration and validation Signal Photodiode DAQ Diode Laser AIR Signal photodiode Auxiliary heater Exhaust valve Heater controller Windows Absorption cell TC 4 TC 3 TC 2 TC 1 Reference Photodiode Fiber coupler Diode Laser

41. Optically accessible bipolar plate  Same plate design for anode and cathode  Optically accessible plates  Effective flow path is 7 cm BIPOLAR PLATE Measurement averaged along channel length

42. Laser system l Laser temperature tuned over ~5 nm to couple with different H 2 O transitions l Laser current tuning affects both power and wavelength (0.4 nm) l Laser power monitored by photodiode l All measurements on cathode side of the fuel cell Beamsplitter Reference Photodiode To experiment/ Test cell Laser Current Controller

43.  Laser current modulated by 100 Hz ramp function  Single scan range of 0.4 nm  Laser wavelength calibrated with a ring interferometer system  Multiple scans averaged Measurement Methodology Test Cell Signal Photodiode Reference Photodiode Current Ramp Output Ln (sig/ Ref)

44. Signal processing (1) l Measurements of reference and signal photodiode are imposed on current ramp

45. Signal processing (2) l Four Lorentzian profiles and a polynomial background fit to measured signal l Sum of four Lorentzian represents Log(Signal/Reference)

46. Partial pressure extraction Widths of two strong transitions are assumed equal based on HITRAN Simulation Intensities of two strong transitions are assumed constant multiples of one another for all Ps and T.  Six curve fit parameters: 2 widths, 3 intensities, background Empirically, self-broadening and air broadening are related by:  Partial pressure directly related to measured transition width

47. Partial pressure determination l Calibration experiments performed in fuel cell geometry with controlled temperature and relative humidity 10 % Error

48. Operating Fuel Cell Setup Laser Data Acquisition and Laser controller Electric Load Box Temperature Controller Current Controller Fuel Cell Control H2H2 Air TC1 TC2TC3 Humidifiers PD1 PD2 Scribner Fuel Cell Test Station

49. Experimental conditions Absorption data collected twice for each current setting & averaged For each data set curve fit was done Partial Pressure predicted from measured half width using calibration line

50. Measurements in active fuel cell (Cathode side) Measured water partial pressure in operating fuel cell at inlet water partial pressures of (a) P s = 0.19 atm and (b) P s = 0.26 atm for a cell temperature of 80 ºC l Experimental data collected show a similar increase in partial pressure with current density l Diagnostic technique works for high current densities if the inlet relative humidity is less than 80 %. Temperature insensitive measurement

51. Theoretical study for the determination of temperature and partial pressure simultaneously Present laser source stimulated transitions insensitive to temperature For 20 o C rise in temperature a temperature sensitivity of atleast 20 % is needed. 23 % variation in intensity detected for transition in the range of 1470 nm

52. Calibration with new Laser for simultaneous temperature and partial pressure detection Partial Pressure and Temperature Calibration Partial Pressure calibration same as before Temperature is calibrated from peak intensity

53. Measurement Under Steady State Conditions Temperature and partial pressure detected from single laser scan For a steady state cell with controlled temperature the measured temperature is about 55 ºC

54. Measurement under dynamic fuel cell operation Partial pressure rise upto 0.3 atm from the inlet value of 0.19 atm entire dynamic cycle of 300 secs Temperature rise is recorded for each cycle above the steady state value of 80 ºC. Temperature as high as 90 ºC is observed.

55. Spatially Resolved Measurements (Steady State) Measurements across two channels simultaneously using a single laser scan Difference in partial pressure between two channels increases with current load

56. Spatially Resolved Measurements (Steady State) Difference in partial pressure between two channels increases with current load Temperature across both channels are similar

57. Spatially Resolved Measurements (Dynamic) Measurements across two channels simultaneously using a single laser scan Load is varied sinusoidally Partial pressure closely follows the load profile without phase lag

58. Concluding Remarks  In situ water vapor concentration measurements demonstrated using tunable diode laser absorption spectroscopy in PEMFC  Calibration measurements permit partial pressure determination within 10% accuracy and +/- 2 ºC for temperature  Measurements in operating fuel cell show strong signals with low noise  Simultaneous detection of temperature and H 2 O partial pressure  Measurements in the fuel cell under dynamic and steady state conditions  Spatially resolved measurements permit simultaneous determination of temperature and pressure across two channels  FM spectroscopy will allow higher degree of accuracy in H 2 O measurements as well as allowing to measure other species such as CO, CO 2

59. Acknowledgments l This work was sponsored by a grant from U. S. Army Research RDECOM, CERDEC (Fort Belvoir, VA) through Connecticut Global Fuel Cell Center (CGFCC) l I acknowledge the contributions of the following people: l Profs. B.M Cetegen (Advisor), M.W Renfro (Co-advisor), E.H Jordan (Co-advisor) l Prof. J. Fenton, Drs. M. Williams and V. Ramani for allowing us to use their fuel cell set-up l Mr. T. Mealy for technical help in machining l Dr. Haluk Gorgan and Prof. F. Barbir for allowing us to use their fuel cell set-up

60. Limitations of Current Technique and Future Plans The spatial resolution was limited to average value along channel length. Pointwise measurements needed The temporal resolution of the technique inadequate for high frequency load cycle Cyclic loading can lead to unforeseen effects in species transport and temperature distribution. Timescale of load variation and species kinetics mismatch. Result malfunctioning like water logging or drying up of the cell The modes of failure for a cyclic load compared to steady state operation Durability will be different for same load.

61. Future Research Directions (I) Pointwise resolvable measurements across each channel Extension of the measurement technique to include species like CO Extension of the methodology to direct methanol fuel cell (DMFC) Improved temporal resolution of the technique to quantify the response characteristics of the gas phase subjected to high frequency load cycle Potential extension to include high temperature fuel cell like SOFC Developing novel diagnostics techniques for two-phase flow characteristics, thermal transport within the gas channels and the MEA Novel imaging techniques and optical sensors for fuel cell testing and real time feedback control strategy Extension to fuel cell stacks Measurements in cold weather start up

62. Future Research Directions (II) In-situ infrared fiber evanescent wave spectroscopy using tunable laser for pointwise measurements of concentration both in the vapor and liquid phases FUNDING [CBET/DOE[EERE]/ US ARMY/ FSEC] High speed imaging for monitoring growth and dynamics of liquid water from the MEA at high power FUNDING [CBET/ DOE[EERE]/ PRIVATE SECTOR/COLLABORATION FSEC] PIV measurements to observe velocity and clogging in the channels FUNDING [CBET/ DOE[EERE]/ PRIVATE SECTOR/ COLLABORATION FSEC] FM Spectroscopy to increase temporal resolution of the measurements FUNDING [CBET/ DOE[EERE]/ US ARMY/ FSEC] 3D modeling to understand the response especially the short time transients [COLLABORATION UCONN]

63. CCD Camera Laser Sheet Embedded, Unclad, Flattened Optical Fiber for Evanascent Spectroscopy Strobe Light Water Droplets Water Film Water Vapor Zone Transparent optically accessible Plate with Anti-Fog coating Current Collector COMPLETE UNDERSTANDING OF WATER TRANSPORT

64. Frequency Modulation (FM) Spectroscopy Schematics of a single laser FM spectroscopy To measure weak transitions in other wavelength regions which are very sensitive to temperature Reduce the error band arising principally due to large background.

65. Preliminary FM Spectra SimulatedExperimental Initial data(2f) taken under ambient conditions at a temperature of 25 o C at a partial pressure of 0.013 atm. The profile looks very clean with negligible background.

66. Outcomes Complete understanding of the transport of water vapor and other species under steady and dynamic conditions Chemical kinetics of the of the fuel cell under high frequency load cycle as in automobile Inception of two phase flow Growth and transport of liquid water Simultaneous measurement of temperature Extension to SOFC and DMFC Validation of the computational models Partial understanding of the durability issue of the fuel cell arising through water transport Extension to similar measurements inside the MEA Measurements in fuel cell stacks Measurements during cold weather start up

67. Combined Funding Options NSF [CBET: Transport and Thermal Fluids Phenomena, Energy for Sustainability] DOE [Office of Energy Efficiency and Renewable Energy (EERE) ] ONR U.S. Army Research, Development and Engineering Command Collaboration with Private Company Collaboration with FSEC, UCONN, CGFCC Startup Funding