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    Geometric optimization of an ejector for a 4 kW SOFC system with anode off-gas recycle
    (Elsevier Ltd, 2018) Genc O.; Toros S.; Timurkutluk B.
    One of the important energy saving tools used in solid oxide fuel cell (SOFC) system is the anode off-gas recycling (AGR) via an ejector which allows the recirculation of the unused fuels in the anode exhaust gas including hot steam which is essential for the elimination of the carbon deposition and the initiation of the reactions in the reformer. In an ejector system developed for the SOFCs, the steam to carbon ratio (STCR) and entrainment ratio are the crucial parameters for the determination of the ejector performance. These parameters can be engineered by modifying the geometric dimensions and operation conditions. This study focuses on the determination of the maximum STCR value and entrainment ratio via numerical geometric analyses for a micro combined heat and power (µ-CHP) system based on 4 kW SOFC, utilizing methane. A detailed numerical procedure for designing an ejector is provided and the ejector performance is investigated for different critical dimensions (throat diameter, nozzle exit angle and nozzle position etc.). The results show that the nozzle position and the nozzle exit angle significantly affect STCR and the entrainment ratio. When the nozzle position increases and nozzle exit angle decreases, the entrainment ratio and STCR is found to increase. The entrainment ratio and STCR are determined as around 7.3 and 2.7, respectively for a specific design created in the study. © 2018 Hydrogen Energy Publications LLC
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    Numerical optimization of channel to land width ratio for PEM fuel cell
    (Elsevier Ltd, 2018) Chowdhury M.Z.; Genc O.; Toros S.
    Flow field plays a vital role in proton exchange membrane (PEM) fuel cell where channel geometry being the primary factor. Most of the channel geometry analyses were limited to few number of case studies, whereas in this study total 73 case studies were analyzed for the optimization of channel and land width. A three dimensional isothermal single phase flow mathematical model is developed and further validated with experimental study to optimize the channel and land width through parametric sweep function for a staggering 73 number of case studies. The optimization analyses are carried out for a straight channel geometry considering a fixed operating voltage of 0.4 V and channel depth of 1.0 mm. Due to the large number of case studies, the analyzed performance parameters i.e. current density and pressure drop are easily understandable for the change in different channel and land width. The numerical results predicted that the pressure drop is more dependent on channel width compare to the land width and anode pressure drop is less significant than cathode pressure drop. However, both channel and land width have an equal importance on the cell current density. Considering channel pressure drop and current density, the optimization analyses showed that the channel to land width of 1.0 mm/1.0 mm would be best suitable for PEMFC channel geometry. © 2017 Hydrogen Energy Publications LLC