6.3Rankine Vapor CycleAdvantages:T4IncreaseinWreti T.>T=ntii it decreases the moisture contentof the steam at the turbine exit223Disadvantages:Superheating temperature is limitedby metallurgical considerationst, ≤600℃
3 4 5 1 1’ 2 2’ 6 Advantages: ' i T T 1 1 t ii it decreases the moisture content of the steam at the turbine exit. Disadvantages: Superheating temperature is limited by metallurgical considerations. t 1 600℃ 6.3 Rankine Vapor Cycle
6.3Rankine Vapor Cycle3. P2 - Condenser Pressure, Turbine ExitTt,, Pi-UnchangeP2P265Two Cycles:1)1-2-3-4-5-6-132)1-2'-3'-4'-5-6-12'YIncrease in Wnet1
3. p2－ Condenser Pressure, Turbine Exit , 1 1 t p －Unchange 2 p 2' p Two Cycles: ① 1-2-3-4-5-6-1 ② 1-2’-3’-4’-5-6-1 3 4 5 1 3’ 2’ 2 6 4’ 6.3 Rankine Vapor Cycle
6.3Rankine Vapor CycleT.<T,→n.个Disadvantages:511i Condense pressure is limitedbythe sinktemperature.ii Itincreases themoisture3content which is highly2'Increase in wnetundesirableS
3 4 5 1 3’ 2’ 2 6 4’ ' i T T 2 2 t ii Disadvantages: i Condense pressure is limited by the sink temperature. ii It increases the moisture content which is highly undesirable. 6.3 Rankine Vapor Cycle
6.3Rankine Vapor CycleExampleConsider a steam power plant operating on the ideal Rankinecycle. The steam enters the turbine at 2.5MPa and 350°C andis condensed in the condenser at pressure of 7okPa.Determine(a)The thermal efficiency of this power plant(b)The thermal efficiency if steam is condensed at 10kPa(c)The thermal efficiency if steam is superheated to 60o C(d)The thermal efficiency if the boiler pressure is raised to15MPa while the turbine inlet temperature is maintain at600℃
Example Consider a steam power plant operating on the ideal Rankine cycle. The steam enters the turbine at 2.5MPa and 350℃ and is condensed in the condenser at pressure of 70kPa. Determine (a)The thermal efficiency of this power plant (b)The thermal efficiency if steam is condensed at 10kPa (c)The thermal efficiency if steam is superheated to 600 ℃ (d)The thermal efficiency if the boiler pressure is raised to 15MPa while the turbine inlet temperature is maintain at 600 ℃ 6.3 Rankine Vapor Cycle
State 1:Pi = 2.5MPa,t, = 350℃Th = 3128.2 kJ/kgS = 6.8442 kJ/kg · KT,=350°℃2.5MPaState 2:70kPaP2 = 70kPa, S2 = St2S '= 1.1921kJ/(kg ·K), s2 "= 7.4804kJ/(kg·K)h '= 376.77kJ/kg, h,"= 2660.1kJ/kgSx-s'IdealRankineCyclex=s"-s'6.8442-1.19210.89887.4804 -1.1921h, =h'+xh"= 376.77 + 0.8988 ×2660.1 = 2767.7kJ/kg
State 1: State 2: 1 1 1 1 2.5MPa, 350 3128.2 kJ/kg 6.8442 kJ/kg K = = = = p t ℃ h s Ideal Rankine Cycle 2 2 1 2 2 2 2 70kPa, ' 1.1921kJ/(kg K), '' 7.4804kJ/(kg K) ' 376.77kJ/kg, " 2660.1kJ/kg ' '' ' 6.8442 1.1921 0.8988 7.4804 1.1921 = = = = = = − = − − = = − x p s s s s h h s s x s s h2 ' '' 376.77 0.8988 2660.1 2767.7kJ/kg = + = + = h xh