integration of solid oxide fuel cells and ... - Ea Energianalyse

5. SIMULATION AND RESULTS
5.4 Sensitivity Analysis
In the previous sections some of the most important/interesting parameters
have been examined thoroughly for different of values. In the following
section spider diagrams will be shown for a larger range of parameters,
subdivided in 4 groups: Closest Approach Temperature Differences,
Pressure Losses, Heat Losses, and (other) Key Parameters. For
each group the effect on the electrical efficiency will be shown on the left
graph, and COP ABS,f uel on the right graph. All of the spider diagrams are
for the standard system configuration (Double Stage, Wet Tower, with
Air Preheat).
The Y-axis show the percent increase of the COP (so a COP increase
from 50% to 51% corresponds to 2% on the y-axis). The x-axis generally
shows the percent increase in the input parameters for the standard
configuration, although for the pressure losses in the absorption cycle,
the standard parameter inputs are 0. So for these pressure loses the
percent change is of the absolute pressure in that component. The heat
loss is also 0 in the standard parameter configuration, so here it has been
chosen to let the x-axis go from 0 to 1kW while the fuel input is kept at
100kW.
The y-axis has the same range in all (but one) of the figures (-5% to
5%). This makes it easier to compare the effect of the different groups
of parameters, although it does of course make it harder to see the exact
value of the less important groups - but again: if all parameters in a group
has a very small effect on COP and η sys,el,net their exact value doesn’t
matter much. The only exception is the group ”Key Parameters”, which
has an y-axis going from (-10% to 10%) since some of those parameters
are particularly sensitive.
5.4.1 Closest Approach Temperature Difference
These temperatures have been estimated only based on the type of fluids
in each heat exchanger (water-water, gas-gas etc.), so they are relatively
uncertain, and it is not unlikely that they can be two times as big as
estimated or only half as big (x-values going from -50% to +100%).
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