Methodolgy Table 3. The exergy efficiency of the

MethodolgyExergyis a measure of the maximum capacity of a system to perform useful work as itproceeds to a specified final state in equilibrium with its surroundings.Exergy is not conserved conserved as energy in most cases but instead getsdestroyed in the system. Exergy destruction is actually the irreversibilitythat causes a loss in performance. Therefore, an exergy analysis assessing themagnitude of exergy destruction identifies the location, the magnitude and thesource of thermodynamic inefficiencies in a thermal system.Mass,energy, and exergy balances for any control volume at steady state withnegligible potential and kinetic energy changes can be expressed, respectively,by??i=??eQ-W=??ehe-??ihXheat– W= ??e?e-??i?i + Iwherethe net exergy transfer by heat (Xheat) at temperature T is given byXheat= ?(1-To/T)Qandthe specific exergy is given by?= h-ho –To(s-so)Thenthe total exergy rate associated with a fluid stream becomesX=??= ?h-ho–To(s-so)For a steady state operation, and choosing each component in Fig. 1 as a control volume, the exergy destruction rate and the exergyefficiency are defined as shown in Table 3. The exergy efficiency of the powercycle may be defined in several ways, however, the used definitionwill not only allow the irreversibility of heat transfer to the steamin the boiler to be included, but also the exergy destruction associated withfuel combustion and exergy lost with exhaust gasesfrom the furnace 17.

Note that the fuel specific exergy is calculated as:, where   , is the exergy factorbased on the lower heating value 18. In addition, the pump input power was calculated as ,where , isthe combinedpump/motorefficiency. Table 3:Given Parameters for the Power Plant Points T (K) P (MPa) ? (kJ/kg) h (kJ/kg) s (kJ/kg K) 1 618.55 2.4231 17.80 3118.1 6.8419 2 547.85 1.3244 14.92 2986.9 6.8835 3 463.65 0.5690 16.40 2831.4 6.9511 4 394.35 0.2060 13.96 2707.7 7.1173 5 360.45 0.0628 6.39 2655.2 7.5169 6 343.15 0.0272 204.90 2626.9 7.8193 7 339.95 0.0272 204.90 279.66 0.91588 8 341.15 0.0270 226.00 278.82 0.9134 9 337.60 1.3734 226.00 285.79 0.9299 10 356.15 0.0245 21.10 269.81 0.8868 11 362.45 0.0536 226.00 347.61 1.1111 12 390.15 0.0687 13.96 374.09 1.1848 13 428.15 0.1815 226.00 491.08 1.4954 14 430.15 0.6867 275.00 653.88 1 1.8922 15 436.15 12.2630 275.00 669.49 1.8991 16 461.45 0.6671 32.70 688.52 1.9725 17 466.15 10.7910 275.00 804.43 2.2056 18 494.15 2.3544 17.80 821.28 2.2626 19 793.15 10.3010 275.00 950.46 2.5124 20 793.15 9.1233 275.00 3436.3 6.7168 Input air 298.15 0.1013 23900 424.54 3.8814 Output air 318.15 0.1013 23900 444.68 3.9468

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