Effects of operating conditions on the performance of a micro-tubular solid oxide fuel cell (SOFC)

A parametric analysis is carried out to study the effects of the operating conditions on the performance and operation of a micro-tubular solid oxide fuel cell. The computational fluid dynamics model incorporates mass, momentum, species and energy balances along with ionic and electronic charge transfers. Effects of temperature, fuel flow rate, fuel composition, anode pressure and cathode pressure on fuel cell performance are investigated. Polarization curves are compared to allow an understanding of the effects of different operating conditions on the performance of the fuel cell. Effects of anode flow rate on fuel cell efficiency and fuel utilization are also investigated. Moreover, influence of operating temperature on the internal electronic current leaks is outlined. Temperature distributions, current density profiles and hydrogen mole fraction profiles are also utilized to have a better understanding of the spatial effects of operating parameters. It is predicted that at 550 degrees C, for an output current demand of 0.53 A cm(-2), fuel cell needs to generate 0.65 A cm(-2) ionic current density where the difference in these values is attributed to internal current leaks. On the other hand for temperatures lower than 500 degrees C, the effect of electronic leakage currents are not significant. (C) 2009 Elsevier B.V. All rights reserved.X1130sciescopu

A transient analysis of a micro-tubular solid oxide fuel cell (SOFC)

A two-dimensional, axisymmetric transient computational fluid dynamics model is developed for an intermediate temperature micro-tubular solid oxide fuel cell (SOFC). which incorporates mass, species, momentum, energy, ionic and electronic charge conservation. In our model we also take into account internal current leak which is a common problem with ceria based electrolytes. The current density response of the SOFC as a result of step changes in voltage is investigated. Time scales associated with mass transfer and heat transfer are distinguished in our analysis while discussing the effect of each phenomenon on the overall dynamic response. It is found that the dynamic response is controlled by the heat transfer. Dynamic behavior of the SOFC as a result of failure in fuel supply is also investigated, and it is found that the external current drops to zero in less than 1s. (C) 2009 Elsevier B.V. All rights reserved.X1130sciescopu

Thermal Stresses in an Operating Micro-Tubular Solid Oxide Fuel Cell

A multi-physics model is developed to investigate the thermal stresses in a micro-tubular SOFC, based on a previously developed thermal-fluids model predicting cell operation. Mechanical properties of the anode and cathode are determined theoretically through composite structure approximation. Residual stresses arisen during the fabrication of the cell due to the mismatch in thermal expansion coefficients are calculated by accounting for each fabrication process separately. The interactions between the cell, the sealant and the alumina tube are accounted for a better representation of the actual fuel cell test setup. The effect of sealant and alumina tube on the stress distribution in the cell is investigated and it is found out that near the fuel cell-sealant interface stress distribution changes significantly. The effect of spatial temperature gradient on the stress distribution is also analyzed and found to have a minimal impact for a typical fuel cell operation at mid-range current densities. The effects of oxygen vacancies caused by the reduction of the GDC electrolyte on the overall stress distribution are also shown. Oxygen vacancies of the electrolyte result in relaxation of the stresses due to the alleviation of mismatch in Young's modulus between different layers of the cell. (C) 2010 Published by Elsevier B.V.X1126sciescopu

Computational thermal-fluid analysis of a microtubular solid oxide fuel cell

A computational fluid dynamics model is developed to study the steady-state behavior of a microtubular solid oxide fuel cell (SOFC). The model incorporates mass, momentum, species, and heat balances along with ionic and electronic charge transfers. The anode-supported SOFC studied in this work consists of a ceria-based electrolyte which is known as an electronic conductor in reducing atmospheres, letting electrons leak through the electrolyte. Related internal leakage currents are calculated implicitly in the model to incorporate the performance losses. Moreover, to have a more realistic approach while cutting down the computational effort, in this study a fuel cell test furnace is also modeled separately to evaluate the distribution of the oxygen concentration and temperature field inside the furnace. Results from the furnace model are used as boundary conditions for the fuel cell model. Fuel cell model results are compared with the experimental data which shows good agreement. (c) 2008 The Electrochemical Society.X112330sciescopu