Object-based modeling of SOFC system: dynamic behavior of micro-tube SOFC Tomoyuki Ota a,* , Michihisa Koyama a , Ching-ju Wen a , Koichi Yamada b , Hiroshi Takahashi a a Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan b Department of Fine Materials Engineering, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan Abstract A simulation model for a tubular solid oxide fuel cell (SOFC) was developed by the object-based approach to calculate the current distribution, gas concentration distribution, and temperature distribution at the steady states and transient operation states. The transient electrical and temperature response to a load change was simulated for the both cells with the diameter of 22 mm (standard cell) and the diameter of 2.4 mm (micro-tube cell). The time required to reach the new steady state as the operating voltage was changed from 0.7 to 0.5 V for the micro-tube cell was found to be 15 s, which is much shorter than that of the standard cell. # 2003 Elsevier Science B.V. All rights reserved. Keywords: SOFC; Modeling; Object-based; Transient characteristics 1. Introduction Solid oxide fuel cell (SOFC) has many advantages due to its high operation temperature, such as high energy conver- sion efficiency, flexibility of usable fuel type, and high temperature exhaust gas. However, the rapid start-up of SOFC is difficult due to its high operation temperature, so a good promise of the SOFC system as a stationary power supply system was mainly surveyed [1,2]. Recently, it is proved that SOFC with micro-tube cell having diameters of 2 mm could be heated up to operation temperature within a few seconds without any crack [3]. Further, micro-tube cells can reduce the system volume and therefore increase the output power density, because the effective electrode area per unit volume increases by decreasing the cell diameter. The higher output power density, in conjunction with the high tolerance to thermal stress makes it possible to apply SOFC systems as the power supply to vehicles [4,5]. During the operation of an SOFC system, the suppression of mechanical stress and the quick system response to a demand change are important. Mechanical stress, which leads to the mechanical breakdown of the cell components, can be classified into two types, i.e. residual thermal stress through fabrication and thermal stress caused by the tem- perature distribution along the cell. In order to design the cell and stack, which can prevent the mechanical breakdown, the analysis of the temperature distribution is first necessary. Further, to apply SOFC systems to vehicles, it is important to investigate the transient characteristics of the SOFC. Although such analyses by experimental approach are necessary, it is time consuming to investigate the character- istics for all the cells at various operating conditions only by experimental approach to optimize the system design. Com- putational modeling is an effective tool for designing the optimal SOFC system and for predicting their characteristics at the steady states and transient operating states. The transient electrical response of a planar cell [6] and a tubular cell [7,8] has been studied using the conventional cell component materials. However, we are not aware of any previous literature reporting the transient characteristics of SOFC for different cell and stack configurations and cell component materials on the same basis. While there is a strong need to compare SOFC with different cell configuration and different cell components, an analysis and designing of the SOFC system requires interdisciplinary collaborations. An object-based modeling approach can work effectively for the interdisciplinary collaboration [9]. In an object-based model framework, each component model is modularized as an object with explicit interface. By defining the interfaces explicitly, each modeler only needs to assure that the interface of his or her own Journal of Power Sources 118 (2003) 430–439 * Corresponding author. 0378-7753/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0378-7753(03)00109-5