Page 125 - Entrophy Analysis in Thermal Engineering Systems

118 Entropy Analysis in Thermal Engineering Systems

Table 8.2 The effect of heat exchanger effectiveness on the maximum thermal
efficiency and minimum specific entropy generation of the regenerative gas
turbine cycle.
Simple cycle e50.55 e50.65 e50.75 e50.85 e50.95
0.370 0.380 0.394 0.415 0.448 0.512
η max
SEG min (J/molK) 1771 1741 1705 1652 1567 1403

TIT¼1273K, η c ¼0.85, and η t ¼0.90. So, the efficiency limit would
change with a change in TIT, η c ,or η t .
Fig. 8.6 depicts the distribution of SEG throughout the cycle at the con-
dition of minimum SEG for three different values of E. Like in the simple gas
turbine cycle, the combustion process and flue gases cooling are the two
major SEG contributors. Evident from Fig. 8.6 is that an improvement in
the effectiveness leads to a reduction in the SEG share of both combustion
and cooling processes indicating that the thermal energy is utilized more effi-
ciently. On the other hand, the heat exchanger contribution to SEG
increases with an increase in the effectiveness, which is due to an increased
heat transfer within the recuperator. The combined SEG share of the com-
pressor and turbine remains relatively unaltered. The net reduction in the
combined SEG share of the combustion and cooling processes exceeds

Fig. 8.6 Distribution of the specific entropy generation throughout the regenerative
gas turbine cycle at minimum SEG for three values of E (TIT¼1273 K, η c ¼0.85, η t ¼0.90).