Journal of Power Sources 204 (2012) 14–24 Contents lists available at SciVerse ScienceDirect Journal of Power Sources jou rn al h om epa ge: www.elsevier.com/locate/jpowsour Selection of suitable operating conditions for planar anode-supported direct-internal-reforming solid-oxide fuel cell Suranat Wongchanapai ∗ , Hiroshi Iwai, Motohiro Saito, Hideo Yoshida Department of Aeronautics and Astronautics, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto 606-8501, Japan a r t i c l e i n f o Article history: Received 18 October 2011 Received in revised form 8 December 2011 Accepted 13 December 2011 Available online 8 January 2012 Keywords: Anode-supported Direct internal reforming SOFC Exergy analysis Inlet temperatures Material constraints a b s t r a c t A numerical model was implemented to analyze the thermodynamic performance of the co- and counter- flow operations of an anode-supported direct internal reforming (DIR) planar solid oxide fuel cell (SOFC). This developed model was validated by comparing with experimental and simulated results taken from the literature. The model is capable of capturing the detailed distribution of the local temperatures, species concentrations, current density, and polarization losses in streamwise direction. Energy and exergy con- cepts were used to evaluate the DIR-SOFC performance under co- and counter-flow operations. The study indicates the energy and exergy efficiencies of DIR-SOFC performance under co-flow operation are more sensitive to the increase of current density than that under counter-flow operation. Particular attention was paid to cell temperature profiles to avoid mechanical failure due to high thermal stresses. The result shows that the material constraints need to be considered as well as the energy and rational efficiencies in evaluating the performance of SOFC. The preferred flow configuration can be changed depending on the cell geometry and operation conditions if we consider the material constraints. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Among fuel cells, high operating temperature SOFCs could improve and promote the exploitation of power generation system as combined heat and power systems to raise the energetic effi- ciency [1–7]. Furthermore, high operating temperature SOFCs also offer many advantages over other fuel cells (i.e., fuel flexibility, tol- erance to impurities). However, this high operating temperature poses a problem in terms of the thermal management of SOFCs [8]. Because SOFCs are made of fragile ceramic materials, a large tem- perature gradient may cause cracking of the cell. It is required to properly control the cell temperature distribution for its safe and efficient operation. One of the attracting features of SOFC is the direct internal reforming (DIR) of hydrocarbon fuels. The endothermic reforming reaction proceeds on the Ni catalyst in the anode in the direct inter- nal reforming process. It utilizes the waste heat generated by the electrochemical reaction and other irreversible processes to offset the heat requirements of the reforming reaction, resulting in the increase in the performance of the SOFC. It also reduces the amount of the extra air supplied to the cathode channel because the cool- ing demand is reduced, thus lowering the cost. One drawback is that it may cause a large temperature gradient to the cell because ∗ Corresponding author. Tel.: +81 75 753 5203; fax: +81 75 753 5203. E-mail address: suranat.w@hs8.ecs.kyoto-u.ac.jp (S. Wongchanapai). of the strong endothermic nature of the reforming reaction. How- ever, direct measurements of the temperature distribution in an operating DIR-SOFC are difficult because of the high temperature, narrow channel gaps, and small flow rates. Numerical simulation is expected to be an effective tool to understand the phenomena in a DIR-SOFC system. CFD-based two- and three-dimensional simulations of fuel cells can be found in the literature [9–11] but owing to the heavy computational load, the computational domain is generally limited to a single module or channel. Iwai et al. [12] recently developed a CFD based quasi-three-dimensional simulation model that applies the volume-averaging method to the flow passages by assuming that a porous material is inserted as a current collector. It reduces the computational time and cost while maintaining the ability to solve the flow and pressure fields in the SOFC. The CFD based simulation is effective to investigate detailed phenomena in the SOFC but it is an expensive computational process for a system level analysis where modules are usually described with lumped (0-dimensional) models. The use of the lumped model to DIR-SOFC, however, needs to be carefully examined before its application to a system analy- sis because the large temperature gradient expected in a DIR-SOFC and its effects cannot be taken into account if a lumped model is used. To consider the distributions of variables in the DIR-SOFC, 1-D model is at least needed. Campanari [13] proposed two-dimensional CFD based numer- ical models for electrolyte-supported DIR-SOFC. They performed parametric analysis on the effects of heat losses, air ratio and cell 0378-7753/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2011.12.029