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Student Number 93343037 Author Chia Ming(黃家明) Author's Email Address 93343037@cc.ncu.edu.tw Statistics This thesis had been viewed 1505 times. Download 780 times. Department Mechanical Engineering Year 2009 Semester 1 Degree Ph.D. Type of Document Doctoral Dissertation Language English Title Optimizations of Flow Distributors and Anodic Microstructures for Planar SOFC Date of Defense 2010-01-26 Page Count 95 Keyword anodic microstructures cell tests flow uniformity numerical simulations solid oxide fuel cell Abstract This thesis aims to study two facets of the polarization problems in planar solid oxide fuel cells (SOFC) concerning optimization of both flow distributors and anodic microstructures with an emphasis on the degradation mechanisms due to effects of flow uniformity in flow channels and flow resistances in porous electrodes. The first objective is to investigate the effect of flow uniformity in various flow distributors to the cell performance of planar SOFC using both numerical simulations and experimental measurements. The former involves several 3-D numerical models implemented by CFD-RC packages which have been used to simulate various hydraulic rib-channel experiments previously performed by Yen (2004) in our laboratory. Numerical flow data were found in good agreement with the experimental results obtained by Yen (2004). Then the validated numerical models were used to evaluate the effect of flow uniformity modulating by various different designs of flow distributors to the cell performance of a single-cell stack. It was found that a new design, using simple small guide vanes equally-spaced around the feed header of the double-inlet/single-outlet module, can effectively improve the degree of flow uniformity in flow distributors resulting in 11% increase of the peak power density (PPD). For experimental measurements, a test rig was established, so that the power-generating characteristics as well as the ac impedance spectra of the single-cell stack using different designs of flow distributors can be measured. The goal is to show how exactly the cell performance would vary with a change in the degree of flow uniformity in these aforementioned flow distributors. We found that by improving the degree of flow uniformity in flow distributors, values of PPD of the single-cell stack can be indeed increased up to 14%. Furthermore, we also found that the ohmic resistance and the low-frequency arc of the single-cell stack can be reduced respectively 32% and 40% when using the optimal flow distributors and the operating voltage is set at 0.6 V.

The second objective is to investigate effects of porosity (e), permeability (k) and tortuosity (t) of anodic microstructures to the cell performance of a single-unit planar anode-supported SOFC using 3-D electrochemical flow models with measured porous transport properties. In particular, we measured an effective viscosity (mu_e) in the Brinkman equation commonly used to predict flow properties in porous electrodes of SOFC. It is found that, contrary to the popular scenario, mu_e is not equal to the fluid viscosity (mu_f), but it is several orders in magnitude smaller than mu_f. This difference can result in more than 10% difference on values of PPD. Our numerical analyses reveal three points. (1) While keeping k and ? fixed with e varying from 0.2 to 0.6, the highest PPD occurs at e = 0.3 where the corresponding triple-phase-boundary length is a maximum. (2) The value of PPD increases slightly with k when k ≤ 10-11 m2 because of the diffusion limitation in anode. (3) The value of PPD decreases with t when t > 1.5 due to the accumulation of non-depleted products. Hence, a combination of e = 0.3, k = 10-11 m2, and t = 1.5 is suggested for achieving higher cell performance of planar SOFC. These results should be useful for further improving cell performance and longevity of planar SOFCs.Table of Content 中文摘要i

各章中文一頁總結ii

Abstractx

致謝xii

List of Tablesxiv

List of Figuresxv

Chapter 1 Introduction1

1.1 Solid Oxide Fuel Cells1

1.2 Why and What to Study?3

1.2.1 Effect of Flow Uniformity3

1.2.2 Effect of Anodic Microstructures5

1.3 Thesis Outline7

Chapter 2 Literature Review12

2.1 Researches on Optimization of Flow Distributors12

2.2 Researches on Flow Dynamics at Porous Interface15

2.3 Researches on Optimization of Anodic Microstructures20

2.4 Researches on AC Impedance Measurements of SOFCs22

Chapter 3 Experimental Methods33

3.1 Test Rig33

3.2 Testing Platform34

Chapter 4 Numerical Methods43

Chapter 5 Numerical Results for Optimization of Flow Distributors51

5.1Flow Uniformity in Various Flow Distributors51

5.2 Effect of Flow Uniformity on Cell Performance52

5.3Effect of Reynolds Number on Cell Performance54

Chapter 6 Numerical Results for Optimization of Anodic Microstructures62

6.1 Effect of Viscosity Ratio on Velocity Profile in Porous Channel62

6.2 Effect of Viscosity Ratio on Cell Performance63

6.3 Effect of Anodic Microstructures on Cell Performance65

Chapter 7 Performance Measurements of Single-Cell Stacks73

7.1 Effect of Flow Uniformity on Cell Performance73

7.2 Variations of Impedance Spectra with Flow Uniformity75

Chapter 8 Conclusions and Future Work85

8.1 Conclusions85

8.2 Recommendations for Future Work86

References88Reference Ackmann, T., de Haart, L.G.J., Lehnert, W. and Stolten, D., Modeling of mass and heat transport in planar substrate type SOFCs, J. Electrochem. Soc., Vol. 150, pp. A783-A789, 2003.

Adler, S.B., Lane, J.A. and Steele, B.C.H., Electrode kinetics of porous mixed-conducting oxygen electrodes, J. Electrochem. Soc., Vol. 143, pp. 3554-3564, 1996.

Agelinchaab, M., Tachie, M.F. and Ruth, D.W., Velocity measurement of flow through a model three-dimensional porous medium, Phys. Fluids, Vol. 18, No. 017105, pp. 1-11, 2006.

Aguiar, P. Adjiman, C.S. and Brandon, N.P., Anode-supported intermediate temperature direct internal reforming solid oxide fuel cell. I: model-based steady-state performance, J. Power Sources, Vol. 138, pp. 120-136, 2004.

Autissier, N., Larrain, D., Van herle, J. and Favrat, D., CFD simulation tool for solid oxide fuel cells, J. Power Sources, Vol. 131, pp. 313-319, 2004.

Barfod, R., Mogensen, M., Klemensø, T., Hagen, A., Liu, Y.L. and Hendriksen, P.V., Detialed characterization of anode-supported SOFCs by impedance spectroscopy, J. Electrochem. Soc., Vol. 154, pp. B371-B378, 2007.

Barsoukov, E. and Macdonald, J.R., Impedance spectroscopy theory, experiment, and applications, 2nd Ed., John Wiley & Sons, Inc., New Jersey, 2005.

Beavers, G.S. and Joesph, D.D., Boundary conditions at a naturally permeable wall, J. Fluid Mech., Vol. 30, pp. 197-207, 1967.

Bear, J., Dynamics of Fluids in Porous Media, Dover Publications, New York, 1988.

Beale, S.B., Lin, Y., Zhubrin, S.V. and Dong, W., Computer methods for performance prediction in fuel cells, J. Power Sources, Vol. 118, pp. 79-85, 3003.

Boersma, R.J. and Sammes, N.M., Computational analysis of the gas-flow distribution in solid oxide fuel cell stacks, J. Power Sources, Vol. 63, pp. 215-219, 1996.

Brandon, N.P., Skinner, S. and Steele, B.C.H., Recent advances in materials for fuel cells, Annu. Rev. Mater. Res., Vol. 33, pp. 183-213, 2003.

Brinkman, H.C., A calculation of the viscous force exerted by a flowing fluid on a dense swarm of particles, Appl. Sci. Res., Vol. A1, pp. 27-34, 1947.

Chen, S.H. and Xia, Z.T., Polarization effects in electrolyte/electrode-supported solid oxide fuel cells, J. Appl. Electrochem., Vol. 32, No. 3, pp. 339-347, 2002.

Chien, C.W., DPIV measurements of gaseous porous ducts for planar SOFC, National Central University, Taiwan, Master Thesis, 2005.

Chyou, Y.P., Chung, T.D., Chen, J.S. and Shie, R.F., Integrated thermal engineering analyses with heat transfer at periphery of planar solid oxide fuel cell, J. Power Sources, Vol. 139, pp. 126-140, 2005.

Costamagna, P. Costa, P. and Antonucci, V., Micro-modeling of solid oxide fuel cell electrodes, Electrochim. Acta, Vol. 43, pp. 375-394, 1998.

Costamagna, P., Arato, E., Achenbach, E. and Reus, U., Fluid dynamic study of fuel cell devices: simulation and experimental validation, J. Power Sources, Vol. 52, pp. 243-249, 1994.

Cui, D., Liu, L., Dong, Y. and Cheng, M., Comparison of different current collecting modes of anode supported micro-tubular SOFC through mathematical modeling, J. Power Sources, Vol. 174, Issue 1, pp. 246-254, 2007.

Danilov, V.A. and Tade, M.O., A CFD-based model of a planar SOFC for anode flow field design, Int. J. Hydrog. Energy, Vol. 34, pp. 8998-9006, 2009.

de Haart, L.G.J., Vinke, I.C., Janke, A., Ringel, H. and Tietz, F., New developments in stack technology for anode substrate based SOFC, in: Yokokawa, H. and Singhal, S.C. (Eds.), 7th International Symposium on Solid Oxide Fuel Cells (SOFC VII), The Electrochemical Society Proceedings Series, Pennington, New Jersey, pp. 111-119, 2001.

Deng, X. and Petric, A., Geometrical modeling of the triple-phase-boundary in solid oxide fuel cells, J. Power Sources, Vol. 140, pp. 297-303, 2005.

Dokamaingam, P., Assabumrungrat, S., Soottitantawat, Sramala, I. and Laosiripojana, N., Modeling of SOFC with indirect internal reforming operation: comparison of conventional packed-bed and catalytic coated-wall internal reformer, Int. J. Hydrog. Energy, Vol. 34, Issue 1, pp. 410-421, 2009.

Durlofsky, L. and Brady, J.F., Analysis of the Brinkman equation as a model for flow in porous media, Phys. Fluids, Vol. 30, No. 11, pp. 3329-3340, 1987.

Fukunaga, H., Ihara, M., Sakaki, K. and Yamada, K., The relationship between overpotential and the three phase boundary length, Solid State Ionics, Vol. 86-88, pp. 1179-1185, 1996.

Gemmen, R.S., Williams, M.C. and Gerdes, K., Degradation measurement and analysis for cells and stacks, J. Power Sources, Vol. 184, Issue 1, pp. 251-259, 2008.

Gilver, R.C. and Altobelli, S.A., A determination of the effective viscosity for the Brinkman-Forchhiemer flow model, J. Fluid Mech., Vol. 258, pp. 355-370, 1994.

Gong, M., Liu, X., Trembly, J. and Johnson, G., Sulfur-tolerant anode materials for solid oxide fuel cell application, J. Power Sources, Vol. 168, pp. 289-298, 2007.

Haanappel, V.A.C. and Smith, M.J., A review of standardising SOFC measurement and quality assurance at FZJ, J. Power Sources, Vol. 171, pp. 169-178, 2007.

Hernández-Pacheco, E., Singh, D., Hutton, P.N., Patel, N. and Mann, M.D., A macro-level model for determining the performance characteristics of solid oxide fuel cells, J. Power Sources, Vol. 138, pp. 174-186, 2004.

Hilpert, K., Das, D., Miller, M., Peck, D.H.and Wei?, R., Chromium vapor species over solid oxide fuel cell interconnect materials and their potential for degradation processes, J. Electrochem. Soc., Vol. 143, pp. 3642-3647, 1996.

Hirata, H., Nakagaki, T. and Hori, M., Effect of gas channel height of gas flow and gas diffusion in a molten carbonate fuel cell stack, J. Power Sources, Vol. 83, pp. 41-49, 1999.

Hou, K. and Hughes, R., The kinetics of methane steam reforming over a Ni/?-Al2O catalyst, Chem. Eng. J., Vol. 82, pp. 311-328, 2001.

Huang, C.M., Shy, S.S. and Lee, C.H., Experimental and numerical studies on flow uniformity in interconnects and its influence to a single planar solid oxide fuel cell, ECS Transactions, Vol. 7, No. 1, pp. 1849-1858, 2007.

Huang, Q.A., Hui, R., Wang, B. and Zhang, J., A review of AC impedance modeling and validation in SOFC diagnosis, Electrochem. Acta, Vol. 52, pp. 8144-8164, 2007.

Iwanschitz, B., Sfeir, J., Mai, A. and Michael, S., Degradation of SOFC anodes upon redox cycling: a comparison between Ni/YSZ and Ni/CGO, J. Electrochem. Soc., Vol. 157, pp. b269-b278, 2010.

Iwata, T., Characterization of Ni-YSZ anode degradation for substrate-type solid oxide fuel cells, J. Electrochem. Soc., Vol. 143, pp. 1521-1525, 1996.

Jorcin, J.B., Orazem, M.E., Pébére, N. and Tribollet, B., CPE analysis by local electrochemical impedance spectroscopy, Electrochem. Acta, Vol. 51, pp. 1473-1479, 2006.

Joshi, A.S., Grew, K.N., Peracchio, A.A. and Chiu, W.K.S., Lattice Boltamann modeling of 2D gas transport in a solid oxide fuel cell anode, J. Power Sources, Vol. 164, pp. 631-638, 2007.

Kakaç, S., Pramuanjaroenkij, A. and Zhou, X.Y., A review of numerical modeling of solid oxide fuel cells, Int. J. Hydrog. Energy, Vol. 32, pp. 761-786, 2007.

Kato, T., Nozaki, K., Negishi, A., Kato, K., Monma, A., Kaga, Y., Nagata, S., Takano, K., Inagaki, T., Yoshida, H., Hosoi, K., Hoshino, K., Akbay, T. and Akikusa, J., Impedance analysis of a disk-type SOFC using doped lanthanum gallate under power generation, J. Power Sources, Vol. 133, pp. 169-174, 2004.

Kee, R.J., Korada, P., Walters, K. and Pavol, M., A generalized model of the flow distribution in channel networks of planar fuel cells, J. Power Sources, Vol. 109, pp. 148-159, 2002.

Kim, C.H., Pyun, S.L. and Kim, J.H., An investigation of the capacitance dispersion on the fractal carbon electrode with edge and basal orientations, Electrochem. Acta, Vol. 48, pp. 3455-3463, 2003.

Klein, J.M., Bultel, Y., Georges, S. and Pons, M., Modeling of a SOFC fuelled by methane: from direct internal reforming to gradual internal reforming, Chem. Eng. Sci., Vol. 62, pp. 1636-1649, 2007.

Koponen, A., Kataja, M. and Timonen, J., Tortuous flow in porous media, Phys. Rev. E, Vol. 54, pp, 406-410, 1996.

Krishnan, V.K., McIntosh, S., Gorte, R.J. and Vohs, J.M., Measurement of electrode overpotenetials for direct hydrocarbon conversion fuel cells, Solid State Ionics, Vol. 166, pp. 191-197, 2004.

Larminie, J. and Dicks, A., Fuel cell systems explained, 2nd Ed., John Wiley & Sons Ltd., England, 2005.

Larrain, D., Solid oxide fuel cell stack simulation and optimization, including experimental validation and transient behavior, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland, Ph.D Thesis, 2005.

Lee, J.H., Heo, J.W., Lee, D.S., Kim, J., Kim, G.H., Lee, H.W., Song, H.S. and Moon, J.H., The impact of anode microstructure on the power generating characteristics of SOFC, Solid State Ionics, Vol. 158, pp. 225-232, 2003.

Lee, K.R., Choi, S.H., Kim, J., Lee, H.W. and Lee, J.H., Viable image analyzing method to characterize the microstructure and the properties of the Ni/YSZ cermet anode of SOFC, J. Power Sources, Vol. 140, pp.226-234, 2005.

Leonide, A., Sonn, V., Weber, A. and Ivers-Tiffée, E., Evaluation and modeling of the cell resistance in anode-supported solid oxide fuel cells, J. Electrochem. Soc., Vol. 155, pp. B36-B41, 2008.

Li, P.W., Chen, S.P. and Chyu, M.K., Novel gas distributors and optimization for higher power density in fuel cells, J. Power Sources, Vol. 140, pp. 311-318, 2005.

Lin, Z., Stevenson, J.W. and Khaleel, M.A., The effect of interconnect rib size on the fuel cell concentration polarization in planar SOFCs, J. Power Sources, Vol. 117, pp. 92-97, 2003.

Lin, C.K., Chen, T.T., Chyou, Y.P. and Chiang, L.K., Thermal stress analysis of a planar SOFC stack, J. Power Sources, Vol. 164, pp. 238-251, 2007.

Liu, H.C., Lee, C.H., Shiu, Y.H., Lee, R.Y. and Yan, W.M., Performance simulation for an anode-supported SOFC using Star-CD code, J. Power Sources, Vol. 167, pp. 406-412, 2007.

Macdonald, J.R., Frequency response of unified dielectric and conductive systems involving an exponential distribution of activation energies, J. Appl. Phys., Vol. 58, pp. 1955-1970, 1985a.

Macdonald, J.R., Generalizations of universal dielectric response and a general distribution-of-activation-energies model for dielectric and conducting systems, J. Appl. Phys., Vol. 58, pp. 1971-19708, 1985b.

Macdonald, J.R., Relaxation in systems with exponential or Gaussian distributions of activation energies, J. Appl. Phys., Vol. 61, pp. 700-713, 1987.

Macdonald, J.R., Analysis of ac conduction in disordered solids, J. Appl. Phys., Vol. 65, pp. 4845-4853, 1989.

Maharudrayya, S., Jayanti, S. and Deshpande, A.P., Flow distribution and pressure drop in parallel-channel configurations of planar fuel cells, J. Power Sources, Vol. 144, pp. 94-106, 2005.

Maharudrayya, S., Jayanti, S. and Deshpande, A.P., Pressure drop and flow distribution in multiple parallel-channel configurations used in proton-exchange membrane fuel cell stacks, J. Power Sources, Vol. 157, pp. 358-367, 2006.

Neal, G. And Nader, W., Practical significance of Brinkman’s extension of Darcy’s law: coupled parallel flows within a channel and a bounding medium, J. Chem. Eng., Vol. 52, pp. 475-478, 1974.

Ni, M., Leung, M.K.H. and Leung, D.Y.C., Parametric study of solid oxide fuel cell performance, Energy Conv. Manag., Vol. 48, pp. 1525-1535, 2007.

Peksen, M., Peters, R., Blum, L. and Stolten, D., Numerical modeling and experimental validation of a planar type pre-reformer in SOFC technology, Int. J. Hydrog. Energy, Vol. 34, pp. 6425-6436, 2009.

Primdahl, S. and Mogensen, M., Gas diffusion impedance in characterization of solid oxide fuel cell anode, J. Electrochem. Soc., Vol. 146, pp. 2827-2833, 1999.

Qu, Z., Aravind, P.V. and Woudstra, N., Flow distribution and pressure variation in the manifolds of SOFC stack, 8th European SOFC Forum, Lucerne, Switzerland, 2008.

Sangani, A.S. and Behl, S., The planar singular solutions of Stokes and Laplace equations and their application to transport processes near porous surfaces, Phys. Fluids, Vol. A1, pp. 21-37, 1989.

Selçuk, A., Merere, G. and Atkinson, A., The influence of electrodes on the strength of planar zirconia solid oxide fuel cells, J. Mater. Sci., Vol. 36, pp. 1173-1182, 2001.

Schiller, C.A. and Strunz, W., The evaluation of experimental dielectric data of barrier coatings by means of different models, Electrochem. Acta, Vol. 46, pp. 3619-3625, 2001.

Shams, M., Study of flow at the interface of a porous media using particle image velocimetry, University of Toronto, Canada, Ph.D Thesis, 1999.

Shams, M., James, D.F. and Currie, G., The velocity field near the edge of a model porous medium, Exp. Fluids, Vol. 35, pp. 193-198, 2003.

Singhal, S.C., Solid oxide fuel cells for stationary, mobile, and military applications, Solid State Ionics, Vol. 152-153, pp. 405-410, 2002.

Singhal, S.C. and Kendall, K., High temperature solid oxide fuel cells: fundamentals, design and applications, Elsevier, Kidlington, 2003.

Song, C., Fuel processing for low-temperature and high-temperature fuel cells: challenges, and opportunities for sustainable development in the 21st century, Catal. Today, Vol. 77, pp. 17-49, 2002.

Stambouli, A.B. and Traversa ,E., Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy, Renew. Sust. Energ. Rev., Vol. 6, pp. 433-455, 2002.

Sun, C. and Stimming, U., Recent anode advances in solid oxide fuel cells, J. Power Sources, Vol. 17, pp. 247-260, 2007.

Tachie, M.F., James, D.F. and Currie, I.G., Velocity measurements of the shear flow penetrating a porous medium, J. Fluid Mech., Vol. 493, pp. 319-343, 2003.

Tachie, M.F., James, D.F. and Currie, I.G., Slow flow through a brush, Phys. Fluids, Vol. 16, pp. 445-451, 2004.

Takeguchi, T., Kikuchi, R., Yano, T., Eguchi, K. and Murata, K., Effect of precieous metal addition to Ni-YSZ cermet on reforming of CH4 and electrochemical activity as SOFC anode, Catal. Today, Vol. 84, pp. 217-222, 2003.

Tikekar, N.M., Armstring, T.J. and Virkar, A.V., Reduction and reoxidation kinetics of Nickel-based SOFC anodes, J. Electrochem. Soc., Vol. 153, pp. 654-663, 2006.

Va?en, R., Simwonis, D. and Stöver, D., Modelling of the agglomeration of Ni-particles in anodes of solid oxide fuel cells, J. Mater. Sci., Vol. 36, pp. 147-151, 2001.

Virkar, A.V., Chen, J., Tanner, C.W. and Kim, J.W., The role of electrode microstructure on activation and concentration polarizations in solid oxide fuel cells, Solid State Ionics, Vol. 131, pp. 189-198, 2000.

Wang, G., Yang, Y., Zhang, H. and Xia, W., 3-D model of thermo-fluid and electrochemical for planar SOFC, J. Power Sources, Vol. 167, Issue 2, pp. 398-405, 2007.

Wilson, J.R., Kobsiriphat, W., Mendoza, R., Chen, H.Y., Hiller, J.M., Miller, D.J., Thornton, K., Voorhees, P.W., Adler, S.B. and Barentt, S.A., Three-dimensional reconstruction of a solid-oxide fuel-cell anode, Nat. Mater., Vol. 5, pp. 541-544, 2006.

Xia, W.S., Yang, Y.Z. and Wang, Q.S., Effects of operations and structural parameters on the one-cell stack performance of planar solid oxide fuel cell, J. Power Sources, Vol. 194, pp. 886-898, 2009.

Yakabe, H., Ogiwara, T., Hishinuma, M. and Yasuda, I., 3-D model calculation for planar SOFC, J. Power Sources, Vol. 102, Issue 1-2, pp. 144-154, 2001.

Yen, C.H., Flow visualization and channel design of bipolar plates for a planar solid oxide fuel cell, National Central University, Taiwan, Master Thesis, 2004.

Yuan, J. Rokni, M. and Sundén, B., Simulation of fully developed laminar heat and mass transfer in fuel cell ducts with different cross-sections, Int. J. Heat Mass Transfer, Vol. 44, pp. 4407-4458, 2001.

Zhao, F. and Virkar, A.V., Dependance of polarization in anode-supported solid oxide fuel cells on various cell parameters, J. Power Sources, Vol. 141, pp. 79-95, 2005.Advisor Shenqyang Steven Shy(施聖洋)

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