Akhtar, Naveed (2010)
Ph.D. thesis, University of Birmingham.
The objective of this work is to compare the performance of different geometries (i.e. planar, coplanar and micro tubular) under single-chamber (mixed-reactant) solid oxide fuel cell (SC-SOFC) conditions. In this respect, these designs have been computer analyzed and it is found that the micro-tubular design eliminates the possibility of cross diffusion/convection from the counter electrode, which is an inherent disadvantage in planar and co-planar designs. This is the first experimental report describing that the micro-tubular design offers the highest fuel utilization, cell efficiency and an acceptable level of performance (under single-chamber conditions) as compared to other designs. With the help of developed numerical model (also the first one, on mixed-reactant, micro-tubular design), it is demonstrated that there is a possibility of further improvement in performance, e.g. cell positioning, micro-tube diameter and cathode morphology (its micro-structure and material) are important factors to consider. Other parameters such as, flow rate, temperature and mixing ratio are also very effective in improving the cell performance but these parameters should be carefully controlled in order to avoid their counter-effects, like, lower fuel utilization, material degradation, anode coking and oxidation-reduction. There are some other parameters such as, electrode porosity, permeability and cathode radiative emissivity, which have minimal effect in performance enhancement and it is suggested before investing time on these parameters, a net energy and cost analysis would be very helpful. There are still some issues with choosing appropriate materials for building an SC-SOFC with both an acceptable lifetime and production of electrical energy. While it has been observed that most of the problems related to material degradation are thermally driven, it would be very helpful to lower the operating temperature by using intermediate temperature SOFC materials. Further to this, long term degradation studies and performance cycling will benefit in order to determine their suitability under mixed-reactant environment.
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