Khaliq Ahmed

Solid oxide fuel cell reactor analysis and optimisation through a novel multi-scale modelling strategy

The simulation of a solid oxide fuel cell (SOFC) that incorporates a detailed user-developed model was performed within the commercial flowsheet simulator Aspen Plus. It allows modification of the SOFCs governing equations, as well as the configuration of the cells fuel-air flow pattern at the flowsheet level. Initially, the dynamic behaviour of single compartment of a cell was examined with a 0D model, which became the building block for more complex SOFC configurations. Secondly, a sensitivity analysis was performed at the channel (1D) scale for different flow patterns. Thirdly, the effect of fuel and air flow rates on the predominant distributed variables of a cell was tested on a 2D assembly. Finally, an optimisation study was carried out on the 2D cell, leading to a robust, optimal air distribution profile that minimises the internal temperature gradient. This work forms the foundation of future stack and system scale studies.

Nernst voltage losses in planar fuel cells caused by changes in chemical composition: effects of operating parameters

Conventionally, the reversible potential at inlet conditions is considered to be the ideal voltage for a fuel cell. However, the reversible potential in planar cells varies along the cell length due to changes in gas composition caused by consumption of fuel and oxidant. This contributes to voltage losses, referred to as Nernst losses, compared to the reversible potential at the inlet of the cell. In the conventional breakdown of cell voltage losses, the variation of reversible potential is not accounted for. To estimate the “true” losses, this needs to be accounted for by employing calculations of the reversible potential with changing composition. This paper quantifies such losses in the context of solid oxide fuel cells (SOFCs) for which they are found to contribute significantly, in the range of 25 to 33% of the total voltage losses. The Nernst equation for fuel cell operation is analyzed and analytical expressions for Nernst losses are derived. The latter allows prediction of the effects of operating parameters which are later verified with an isothermal model of the SOFC.