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ft*saure(Alm)

Figure 6 Figure 7 Figure 8

Figure 6 shows the net power per fuel cell going through a mavimniri From two atmospheres to ten atmospheres, mass flow rate increased slightly above 5%, and the power per solid oxide fuel cell increased 10%. As well, for a reversible Brayton cycle, performance improves with increasing pressure ratio. Thus, one might expect a.monotonic increase in net power, but due to the building influence of turbomachinery inefficiency (25% for the compressor and 20% for the turbine) at higher pressures, hackwork, the ratio of compressor work to turbine work, becomes an increasing factor (it goes towards unity as pressure increases).

The system, efficiencies measured in Figures 7 and 8 do not go through maxima, because even with net work decreasing, the sensible heating needed for the fluid streams leaving the compressor decreases enough to overcompensate the loss in net power. This decrease in sensible heating is again due to turbomachinery. The increase in irreversibility with higher pressure ratios manifests as larger stream temperatures leaving the compressor. As well, for the modified thermal efficiency, high quality waste heat increases with increasing pressure.

The thermal efficiencies have evident trends. The modified thermal efficiencies are consistently 15-20% higher than the electric thermal efficiencies. This emphasizes the importance of considering the high quality heat rejected from the fuel cell stack. Note that the gain in both thermal efficiencies, from one operation pressure to the next, drops off increasingly at higher pressures. It is important to further analyze and understand this asymptotic trend of the thermal efficiencies.

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