Page 52 - Advanced Gas Turbine Cycles

Chapter 3. Basic gas turbine cycles 29

(TsITR = x). Thus each of these elementary cycles has the same Carnot type efficiency,
equal to [l - (TR/Ts)] = [l - (l/x)]. Hence it is not surprising that the whole reversible
cycle, made up of these elementary cycles of identical efficiency, has the same efficiency.
However, the net specific work,

w = (wT - WC) = CpTi[(8/x) - l](x - l), (3.2)
does increase with 8 = T3/T, at a given x. For a given 8, it is a maximum at x = @”.

Although the [CHTIR cycle is internally reversible, extern1 irreversibility is involved
in the heat supply from the external reservoir at temperature TB and the heat rejection to a
reservoir at temperature TA. So a consideration of the intern1 thermal efficiency alone
does not provide a full discussion of the thermodynamic performance of the plant. If the
reservoirs for heat supply and rejection are of infinite capacity, then it may be shown that
the irreversibilities in the heat supply (qB) and the heat rejection (qA), respectively, both
positive, are

3.2.1.2. The reversible recuperative cycle [CHnrl,
A reversible recuperative a/s cycle, with the maximum possible heat transfer from the
exhaust gas, 41. = c,(T4 - Ty), is illustrated in the T,s diagram of Fig. 3.2, where Ty =
T2. This heat is transferred to the compressor delivery air, raising its temperature
to Tx = T4, before entering the heater. The net specific work output is the same as that