TITLE.PM5

GAS POWER CYCLES 669

dharm

\M-therm\Th13-5.pm5

Work

1

Air in

6

Exhaust

¢

L.P.

T

H.P.

C T

2 ¢

C.C 2

4 ¢

35

C.C 1

Reheater

Fig. 13.39. Gas turbine with reheater.

T

s

6 ′

6

5

4 ′

L′

L

4

3

2 ′

2

1

Fig. 13.40. T-s diagram for the unit.
Neglecting mechanical losses the work output of the H.P. turbine must be exactly equal to
the work input required for the compressor i.e., cpa (T 2 ′ – T 1 ) = cpg (T 3 – T 4 ′)
The work output (net output) of L.P. turbine is given by,
Net work output (with reheating) = cpg (T 5 – T 6 ′)
and Net work output (without reheating) = cpg (T 4 ′ – TL′)
Since the pressure lines diverge to the right on T-s diagram it can be seen that the tempera-
ture difference (T 5 – T 6 ′) is always greater than (T 4 ′ – TL′), so that reheating increases the net work
output.