VAPOUR POWER CYCLES 601
dharm
\M-therm\Th12-4.pm53072.5 m + 163.4 – 163.4 m = 762.6
∴ m =
(..
(..762 6 163 4)
3072 5 163 4)−
−
= 0.206 kg of steam flow at turbine inlet. (Ans.)
(iii) Cycle efficiency, ηcycle :ηcycle =
Work done
Heat supplied= −+ −+− ′−′
−+−′11 1 12 3 4 4 5
18 32()()()( )
()()hh hh mh h
hhf hh= −++−
−+−(.).(.)(.)=
(.)( .)3285 3045 6 207 5 1 0 206 715 9
3285 762 6 3280 3045 61015 3
2756 8
= 0.3683 or 36.83%. (Ans.)Highlights
- Carnot cycle efficiency =
TT
T
12
1−- Rankine cycle is the theoretical cycle on which steam primemovers work.
Rankine efficiency = hhhh
f12(^12)
−
−.
- The thermal efficiency of Rankine cycle is increased by
(i)Increasing the average temperature at which heat is added to the cycle.
(ii)Decreasing the average temperature at which heat is rejected to the cycle.
Thermal efficiency of regenerative cycle
()()()( )()
()
hh mhh mmhh
hhf01 112 1 223
011
6−+− − +−− −
−.Objective Type Questions
Choose the Correct Answer :- Rankine cycle efficiency of a good steam power plant may be in the range of
(a) 15 to 20% (b) 35 to 45%
(c) 70 to 80% (d) 90 to 95%. - Rankine cycle operating on low pressure limit of p 1 and high pressure limit of p 2
(a) has higher thermal efficiency than the Carnot cycle operating between same pressure limits
(b) has lower thermal efficiency than Carnot cycle operating between same pressure limits
(c) has same thermal efficiency as Carnot cycle operating between same pressure limits
(d) may be more or less depending upon the magnitudes of p 1 and p 2. - Rankine efficiency of a steam power plant
(a) improves in summer as compared to that in winter
(b) improves in winter as compared to that in summer
(c) is unaffected by climatic conditions
(d) none of the above. - Rankine cycle comprises of
(a) two isentropic processes and two constant volume processes
(b) two isentropic processes and two constant pressure processes