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

5.3. Partial optimization of standard parameters
When ∆T min,W GHE X 3 is decreased, a bigger amount of the energy left
in the exhaust gas can be used to water heating, and furthermore the
temperature to which the water can be heated increases (se figure 5.25).
In the investigation ∆T min has been given the same value in both ends
of the HEX, but in a real system their relationship will be controlled by
the amount of water sent into the HEX (a big water flow means that the
smallest ∆T min will occur at the gas outlet and vice versa). So if ∆T min is
e.g. 15 ◦ C the temperature of the water doesn’t necessarily have to be 67 ◦ C
as shown in the figure. By sending more water through, ∆T min would be
smallest at the gas outlet end, yielding a smaller water outlet temperature
(e.g. to avoid the guests on a hotel from being burned on the hot water
from the tap).
It can be seen from the red curve, that ideally 40% more hot water
could be produced if there were no losses in the HEX (∆T min = 0 rather
than 15 ◦ C).
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