TITLE.PM5

VAPOUR POWER CYCLES 557

dharm

\M-therm\Th12-1.pm5

∴ mf =

5000 0 9

0 5 40000 0 85 0 98

/.

bg

×××

= 0.3335 kg/s or 1200.6 kg/h. (Ans.)

12.3. Modified Rankine Cycle

Figures 12.11 and 12.12 show the modified Rankine cycle on p-V and T-s diagrams (neglecting
pump work) respectively. It will be noted that p-V diagram is very narrow at the toe i.e., point ‘2′’
and the work obtained near to e is very small. In fact this work is too inadequate to overcome
friction (due to reciprocating parts) even. Therefore, the adiabatic is terminated at ‘2’ ; the pressure
drop decreases suddenly whilst the volume remains constant. This operation is represented by the
line 2-3. By this doing the stroke length is reduced ; in other words the cylinder dimensions reduce
but at the expense of small loss of work (area 2-3-2′) which, however, is negligibly small.

p 1

p 2

p 3 m

0 n q

p

v

v 1 v 2

1

2

3

l

2 ′

Fig. 12.11. p-V diagram of Modified Rankine Cycle.

T

s

2

3 2 ′

1

m

l

Fig. 12.12. T-s diagram of Modified Rankine cycle.

The work done during the modified Rankine cycle can be calculated in the following way :

Let p 1 , v 1 , u 1 and h 1 correspond to initial condition of steam at ‘1’.

p 2 , v 2 , u 2 and h 2 correspond to condition of steam at ‘2’.

p 3 , h 3 correspond to condition of steam at ‘3′’.

Work done during the cycle/kg of steam