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Computer simulation and experimental characterization of a tubular micro- solid oxide fuel cell
- Author / Creator
- Amiri, Mohammad Saeid
This work is focused on a state-of-the-art tubular micro-solid oxide fuel cell (TμSOFC), ~3 millimeters in diameter and ~300 microns thick, with Ni/YSZ and LSM/YSZ composite electrodes and a YSZ electrolyte.
A 2D axi-symmetric, multi-scale CFD model is developed which includes the fluid flow, mass transfer, and heat transfer within the gas channels and the porous electrodes. The electrochemical reactions are modeled within the volume of the electrodes, enabling the model to account for the extent of the reaction zone. Thermodynamic expressions are developed to estimate the single-electrode reversible heat generation and the single-electrode electromotive force of a non-isothermal electrochemical cell.
The isothermal, non-isothermal, and transient models are each validated against the experimental results, and consistent with the physical reality of the TμSOFC. A novel approach is used to estimate the kinetic parameters, enabling the simulations to be used as a diagnostic tool.
The model is used to gain a thorough insight about the TμSOFC. The cathode electrochemical activity and the anode support ohmic loss are identified as the two major performance bottlenecks for this cell.
Including radiation is found to be essential for a physically meaningful heat transfer model. The thermoelectric effects on the cell overall electromotive force is found to be negligible. It is found that the anode reaction is always endothermic, while the cathode reaction is always exothermic, and that the temperature gradients across the cell layers are less than 0.05°C
The cell transient response is found to be fast, and dominated by the thermal transients.
Several physical properties used in the model are measured experimentally, indicating that that the correlations used in the literature are not always suitable, especially when new fabrication techniques are used. The conductivity of the anode support was measured to be several orders of magnitude lower than expected and very sensitive to temperature, which explains the lower than expected and occasionally degrading cell performance. A hypothesis is proposed to explain this phenomenon based on the thermal expansion effects which result in the formation and disruption of particle to particle contacts within the composite electrode.
- Graduation date
- Spring 2010
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.