Page 44 - Advanced Gas Turbine Cycles

Chapter 2. Rwersibiliiy and availability 21

An exergy flux statement for the Carnot plant is

[%]CAR = wCAR, (2.28)

where [@N]CAR = J(1 - (TdT3))dQ = mt,RQB and @* is zero.
For the LTB cycle

(2.29)
The difference between Eqs. (2.28) and (2.29) is

Hence,
w, = wc, -Zg -@* -IfR, (2.30)

where

(2.3 1)

and

(2.32)

&, I& may be regarded as irreversibilities of heat supply and rejection in the
LTB cycle. Z$ is the lost work involved in supplying heat QB from a reservoir at a
constant (maximum) temperature T3 to the ITB air heater at temperature T, rather than
to a Carnot cycle air heater at a temperature just below T3. gm is the lost work
involved in rejection of the (larger) quantity of heat QA from the LTB cycle to the
atmosphere.
The thermal efficiency of the LTB cycle is thus less than that of the Carnot plant, by
an amount

(2.33a)

= (dSa>IJB - T, (2.33b)
where 5 and CT are the parameters that were introduced in the simple preliminary analysis
of the ITB cycle given in Chapter 1, Section 1.4. 6 was related to the mean temperatures of
supply and rejection and CT to the ‘widening’ of the cycle.
Thus for a JB cycle, with no internal irreversibility, ZCR = 0 and vjB = 1, from
Eqs. (2.33) and (1.17)

(2.34)