Molten carbonate fuel cells (MCFCs) are electrochemical devices directly converting chemical energy of a redox reaction into electricity: compared with energy conversion by combustion, it is significantly more efficient and less polluting. This paper presents a preliminary study exploring the possibilities of improving the overall MCFC performances, by lowering the cathode polarization. Tests were carried out on single cell systems: these are devices able to simulate full-size plant operation in its essential features. Single cells are constituted by an assembly of porous and metallic components (anode, cathode, matrix, anodic and cathodic current collectors) enclosed by two steel shells. A particular numerical method were used in order to discriminate between the different contributions (anodic polarization, cathodic polarization, internal resistance polarisation and Nernst losses) to the cell's performance reduction during its operation. This method has been applied to specific single cell test, where only cathode working conditions were changed and the cell's response (in terms of voltage changes) was recorded. In this way the cathode's contribution has been identified. These tests have confirmed the possibility of performance improvement possibilities by working on the cathode polarization.

In the present paper the influence of geometrical deviations, related to the manufacturing process or to a different hole positioning over the vane surface, and of coolant Reynolds number on flat plate film cooling through shaped holes are experimentally investigated. Hole geometrical parameters, such as the length of the cylindrical section, hole injection angle, lateral and forward expansion angles were varied and tested for blowing ratio M values between 1.0 and 2.0, also changing the coolant Reynolds number. The dual-luminophore Pressure Sensitive Paint (PSP) technique was used for measuring the adiabatic film cooling effectiveness distribution. Compared with the standard geometry, the V-shaped hole was shown to produce a better thermal protection, especially in the near hole region. Effectiveness is strongly affected by relatively small changes in the hole geometry, like the length of the cylindrical section and the forward expansion angle. A critical coolant Reynolds number was also identified, whose value changes depending on the hole geometry.

This paper describes the design process carried out to develop a new hole geometry. This geometry is able to increase the cooling coverage effect on a turbine blade, in order to have a higher efficiency compared to the standard holes. The first step of the activity described is a CFD analysis of the performances of different hole geometries on a flat plate. Starting from the cylindrical holes the performances of several geometries have been compared. This study allowed the determination of the geometrical parameters mostly responsible of the film effectiveness increase. In this way a criterion able to optimize the hole geometry has been found. Keeping as constraint the same inlet section for all the geometries, the shape of the outlet section was modified in order to maximize the film coverage performances. An optimized hole geometry had been determined. This solution, called V-Shaped hole is characterized by a wide lateral expansion angle and a negligible laidback angle and it is able to increase the cooling effectiveness compared to cylindrical and shaped holes with typical expansion angles (lateral and laidback about 10°). Finally, a comparison with an experimental campaign has been performed to confirm the main results of the CFD analysis.

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This paper describes an experimental activity carried out to investigate the potential of V-shaped holes for film cooling a high-pressure nozzle guide vane. The newly designed V-shaped scheme was compared with a standard laidback fan-shaped holes. The influence of showerhead cooling was also assessed. Different injection conditions were examined under the same cascade operating condition using CO2 as coolant. The quality of holes geometry and their discharging behavior was first characterized. Then dual luminophore Pressure Sensitive Paint (PSP) was used for measuring the adiabatic film cooling effectiveness all over the vane surface. Results of the current work showed that using a V-shaped hole configuration would give nearly the same surface protection as standard shaped holes with a reduced number of holes and, thus, at lower coolant flow consumption.