in Wiley InterScience (www.interscience.wiley.com).A simulation model is developed to analyze steady state and transient operation of a tubular solid oxide fuel cell (SOFC). The performance of the tubular SOFC is compared when the operation parameters such as inlet fuel temperature, inlet oxidant temperature, and inlet oxidant flow rate are changed, respectively. The model includes both electrochemical model and thermal model. The electrochemical model includes the Nernst potential, ohmic polarization, activation polarization, and concentration polarization. The thermal model includes the heat transfer by conduction, convention, and radiation. An analysis is carried out to investigate the effects of the different operation parameters on the hot spot, solid temperature gradient at the steady state, and the response time at the transient state. Numerical results show that the performance of tubular SOFC due to the change of the different operation parameters is different at the steady state. For the transient response such as the same step increase in cell current density, the response time required for the new steady state is different as different operation parameters are changed.

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Experiments on fast transient mass diffusion between a NaCl solution and pure water were conducted. The speed of mass propagation, the concentration profiles, and other quantities were determined experimentally. A physical mechanism that is different from the description of classical diffusion law was revealed by the experiments, and a related theoretical analysis was also made. The results indicate that the calculated results are in good agreement with the experimental data. The modified Ficks formulation more realistically reflects the characteristics of fast transient mass diffusion.