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Title: The Probability of Failure of Solid Oxide Fuel Cells by the Integrated Modelling of Multiple Physical Processes
Author: Clague, Ralph
ISNI:       0000 0004 2681 1055
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2008
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A three dimensional, coupled computational fluid dynamics and finite element model of a single, anode supported solid oxide fuel cell has been developed in order to predict the probability of failure of the ceramic components subjected to an idealised operating duty cycle. The duty cycle represents cooling from sintering, warming to a uniform temperature of 800°C where anode chemical reduction takes place, operation at low, medium and high power and finally cooling to room temperature. The Star CDTM computational fluid dynamics code provided the platform to determine the temperature distribution throughout the operating fuel cell by solving the conservation equations for energy, mass and momentum, with additional subroutines written to account for species transport, electrochemical reactions and heat generation. An Abaqus™ finite element model used the temperature distribution predicted by the computational fluid dynamics model at low, medium and high power to solve for the thermal stress distribution for individual cases and throughout the duty cycle. The finite element model included the effects of thermal expansion, residual stress from manufacture, material properties changes due to chemical reduction of the anode and viscoplastic creep. The maximum principal stress in the anode support layer at 800°C and low, medium and high power was found to be 5.0, 26.5, 33.2 and 39.8 MPa respectively. The stress analysis results were used to determine the time independent and time-dependent (accounting for sub-critical crack growth) probability of failure, and showed that over the duty cycle sub-critical crack growth significantly increased the predicted probability of failure in the anode support layer from less than 1 x 10⁻¹² to 0.54, and in the cathode layer from 1.28 x 10⁻⁵ to 1.24 x 10⁻³. The probability of failure of SOFC ceramic components is thus shown to be both time and history dependent.
Supervisor: Marquis, Andrew ; Travis, Rowland Sponsor: EPSRC ; Supergen Consortium
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral