3-DIMENSIONAL COMPUTATIONAL FLUID DYNAMICS MODELING OF SOLID OXIDE FUEL CELL USING DIFFERENT FUELS by SACHIN LAXMAN PUTHRAN A THESIS Presented to the Faculty of the Graduate School of the MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY In Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE IN MECHANICAL ENGINEERING 2011 Approved by Dr. Umit O. Koylu, Co-Advisor Dr. Serhat Hosder, Co-Advisor Dr. Fatih Dogan Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 3. DATES COVERED 2011 2. REPORT TYPE 00-00-2011 to 00-00-2011 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER 3-Dimensional Computational Fluid Dynamics Modeling of Solid Oxide 5b. GRANT NUMBER Fuel Cell Using Different Fuels 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION Missouri University of Science and Technology,1870 Miner REPORT NUMBER Circle,Rolla,MO,65409 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT Solid oxide fuel cell (SOFC) technology has been of great interest over many years due to its flexibility in using different fuels for operation; including the fundamental fuel i.e. Hydrogen. Various computational and numerical models have been developed along with experimental work to evaluate the performance as well as to identify and overcome the problems faced in the development of SOFC?s. In an attempt to achieve efficient operation with respect to design and combined thermal and electrochemical perspective, the main objective of the proposed study is to present a three-dimensional computational model, which will serve as a framework for the analysis and optimization of SOFC?s. A three-dimensional model of a tubular SOFC was developed to study the effect of temperature and electrolyte thickness variations on its performance. A commercial Computational Fluid dynamics (CFD) software ANSYS FLUENT 12.0 was used for the development of the model which incorporates an interactive 3-D electro-thermo-chemical fluid flow analysis. The particular model, after validation against experimental observations for selected benchmark cases, was demonstrated to be compatible for intermediate temperature operations using hydrogen as fuel. The performance of the model was analyzed by varying electrolyte thicknesses from 2-100 μm. The same model was further evaluated using different fuels such as CH4 (methane) and CO (carbon monoxide), including the modeling of the reformation and the water-gas shift reactions. The results were compared to other computationally less expensive, analytical and empirical models, thus confirming the given model to be used as a basic model for future research on intermediate temperature solid oxide fuel cells. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF ABSTRACT OF PAGES RESPONSIBLE PERSON a. REPORT b. ABSTRACT c. THIS PAGE Same as 83 unclassified unclassified unclassified Report (SAR) Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 2011 Sachin Laxman Puthran All Rights Reserved iii ABSTRACT Solid oxide fuel cell (SOFC) technology has been of great interest over many years due to its flexibility in using different fuels for operation; including the fundamental fuel i.e. Hydrogen. Various computational and numerical models have been developed along with experimental work to evaluate the performance as well as to identify and overcome the problems faced in the development of SOFC’s. In an attempt to achieve efficient operation with respect to design and combined thermal and electrochemical perspective, the main objective of the proposed study is to present a three-dimensional computational model, which will serve as a framework for the analysis and optimization of SOFC’s. A three-dimensional model of a tubular SOFC was developed to study the effect of temperature and electrolyte thickness variations on its performance. A commercial Computational Fluid dynamics (CFD) software ANSYS FLUENT 12.0 was used for the development of the model which incorporates an interactive 3-D electro-thermo-chemical fluid flow analysis. The particular model, after validation against experimental observations for selected benchmark cases, was demonstrated to be compatible for intermediate temperature operations using hydrogen as fuel. The performance of the model was analyzed by varying electrolyte thicknesses from 2-100 μm. The same model was further evaluated using different fuels such as CH (methane) and CO (carbon 4 monoxide), including the modeling of the reformation and the water-gas shift reactions. The results were compared to other computationally less expensive, analytical and empirical models, thus confirming the given model to be used as a basic model for future research on intermediate temperature solid oxide fuel cells. iv ACKNOWLEDGMENTS I would like to thank my advisor Dr. Umit O. Koylu for his guidance, encouragement and financial support throughout this research work. I am also thankful to my co-advisors and also graduate committee members, Dr. Serhat Hosder and Dr. Fatih Dogan for extending their help in relevant topics needed for the research and also for serving in the committee, taking time out of their busy schedules. I am grateful to the Energy Research and Development Center at Missouri University of Science and Technology and the Air Force Research Laboratory (AFRL) for funding my research. I am also grateful to all the faculty members of the department who have contributed in my learning of the required skills to finish this work. I would like to thank all my friends for being with me always in tough times so far away from home. And last, but not the least, I would like to express my gratitude to my parents, my sister and my entire family for their love, affection and support. v TABLE OF CONTENTS Page ABSTRACT.................................................................................................. iii ACKNOWLEDGMENTS........................................................................................ iv LIST OF ILLUSTRATIONS.................................................................................... vii LIST OF TABLES.................................................................................................... viii NOMENCLATURE.................................................................................................. ix SECTION 1. INTRODUCTION........................................................................................ 1 1.1. FUEL CELL THEORY........................................................................ 1 1.2. SOLID OXIDE FUEL CELL THEORY............................................. 5 1.3. OBJECTIVES...................................................................................... 7 2. LITERATURE REVIEW............................................................................ 9 3. SOFC MODELING..................................................................................... 15 3.1. GEOMETRIC MODEL............................................................................... 15 3.2. COMPUTATIONAL MODEL........................................................... 19 3.2.1. Computational Model Theory.................................................... 19 3.2.2. Case Setup.................................................................................. 25 4. MODEL VALIDATION............................................................................. 29 4.1. BOUNDARY CONDITION SETUP................................................... 30 4.2. RESULTS AND ANALYSIS.............................................................. 31 5. PARAMETRIC ANALYSIS....................................................................... 35 5.1. TEMEPRATURE DEPENDENCE & EFFECT OF POROSITY....... 35 5.2. EFFECT OF ELECTROLYTE THICKNESS..................................... 41 5.3. ANALYSIS USING DIFFERENT FUELS......................................... 44 5.3.1. CO Electrochemistry Model...................................................... 44 vi 5.3.2. Modeling the reformation and Water-gas shift reaction using CH as fuel............................................................................ 46 4 6. CONCLUSIONS AND FUTURE WORK.................................................. 54 6.1. CONCLUSIONS AND DISCUSSIONS............................................. 54 6.2. FUTURE WORK SUGGESTIONS..................................................... 55 APPENDIX: FLUENT TUTORIAL FOR SETTING UP THE TUBULAR SOFC MODEL …………………………………………………………….. 57 BIBLIOGRAPHY..................................................................................................... 70 VITA......................................................................................................................... 73 vii LIST OF ILLUSTRATIONS Figure Page 1.1. General architecture of a fuel cell................................................................... 2 1.2. Planar and tubular SOFC configuration........................................................... 5 1.3. Working of SOFC.............................................................................................. 6 3.1. Cross section of tubular SOFC model.............................................................. 17 3.2. Figure showing mesh structure for the model.................................................... 18 4.1. Comparison plot with experimental results from Barzi et al............................. 32 4.2. Plot of power density vs. current density for present model.............................. 33 5.1. Plot of total voltage vs. average current density for different cases with 36 variation in temperature (T) and cathode porosity (p)....................................... 5.2. Power density plotted against average current density for 37 temperature dependence study........................................................................... 5.3. Contour plots of current density, voltage & temperature distribution............... 38 5.4. Plot of H mole fraction over length of cell for all 5 cases................................ 40 2 5.5. Plot of H O mole fraction over length of cell for all 5 cases............................. 40 2 5.6. Plots to study the electrolyte thickness variation effects.................................... 42 5.7.Contour plots of current density, voltage and temperature for CO electrochemistry model..................................................................................... 4 5 5.8.Contour plots of the distribution of fuel species in the flow channel and on electrolyte surface........................................................................................... 49 5.9. Plot showing distribution of H O along length of cell....................................... 51 2 5.10. Contour plots for kinetic rates of reaction........................................................ 52 viii LIST OF TABLES Table Page 1.1.Types of fuel cells.......................................................................................................... 4 3.1. Geometrical properties of the model in study.................................................... 16 3.2. Material specifications for model....................................................................... 26 3.3. Electrical properties of the SOFC model........................................................... 27 4.1. Cell zone conditions and boundary conditions applied to the present model.... 30 5.1. Comparison of results for the model with Stiller et al....................................... 48