Solid oxide fuel cells SOFCRoll single cell and stack design and development
Abstract
This study has focused on the implementation of a stack system for a
novel design of solid oxide fuel cell (SOFCRoll). The issues affecting the
commercialization of SOFCs are mainly based on durability and cost. The new
design offers a number of advantages over the existing designs; it seeks to retain
the specific advantages of both the tubular (high unit strength, no sealing
problems) and planar arrangements (high power density). This design also aims to
achieve low manufacturing cost by utilizing a cheap, easily scalable production
technique: tape casting, together with co-firing all components, in one single step.
In this study aspects of the design and operation of SOFCRoll stacks were
studied particularly those affecting the single cell test reproducibility such as pre
test quality control and scale up issues such as bundle and stack gas distribution.
Initially the performance of single cells was characterized and the variation of
their power output with temperature was observed. The maximum power, 0.7W at
800°C was achieved with a high silver content. The OCV and total resistance of
this cell were 0.93V, 0.30Ω respectively. A standard pre-test quality control and
current collection technique was introduced. At 800°C reproducible performance
of 0.5W power obtained, average OCV was 0.935V and average series and
polarization resistances of 0.18Ω and 0.19Ω was achieved respectively.
Once single cell reproducibility was achieved, the design and operation of
a 5 cell SOFCRoll bundle was investigated. A FLUENT CFD model was used to
optimize the gas distribution in the five cell manifold design. The value of the
model as a design tool was demonstrated by the comparison of 3 different gas
manifold designs. The final manifold design M3 achieved 2.5W which is consistent with the 0.5W per a cell target. This manifold was then used as the
basis for the development of a 25 cell stack which was built and tested. The 25
cell stack testing results were down to 0.35W per a cell. The performance drop
highlighted the problem of fuel cell manufacturing reproducibility and also the
importance of introducing reproducible manufacturing tequniques. That been the
case for single cell manufacturing reproducibility issue, the fundamental concern
for performance drop remains a design issue. To optimize the SOFCRoll design
and to assist with the development program a single-cell CFD model was
developed using FLUENT. The model was validated by comparison with data
from experimental measurements for the single cell. The model work was used to
predict the geometrical effect of the SOFCRoll tubular and the spiral gas channel
configuration and current collector configuration. Results indicate the outlet gas
flow velocity is higher around the spiral, near the gas inlet (the gas interring the
cell preferentially flows around the spiral) therefore, velocity decrease as the gas
moves along the cell. The lowest outlet velocity is registered opposite to the gas
inlet, thus creating non-uniform gas distribution. The current density distribution
is not uniform and is affected primarily by reactant flow distributions along the
cell and possible current collection issues particularly around the spiral part of the
cell.
Type
Thesis, PhD Doctor of Philosophy
Rights
Embargo Date: Electronic copy restricted until 30th October 2015
Embargo Reason: Thesis restricted in accordance with University regulations
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