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Lecture 1
Vapor Power Cycles (Ch-10)
Ideal Rankine Cycle
Thermodynamics - II
Zia Ud Din
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Components of a Vapour Power Plant
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A Real Vapour Power Plant:
A view of the GPU International 80 MW natural gas fired plant adjacent to the Syracuse
University campus in Syracuse NY
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Carnot Cycle
Sadi Carnot French Engineer in 1860 proposed the most efficientthermodynamic cycle called Carnot Cycle
Carnot Cycle is the ideal cycle in which all heat is supplied at one
fixed temp (TH) and all the heat is rejected at a lower fixed
temperature (TL)
Reversible Isothermal Expansion Reversible Adiabatic Expansion
Reversible Isothermal Compression
Reversible Adiabatic Compression
Carnot Cycle consists of 4 reversible
processes. Two isothermal and two
adiabatic
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Carnot Cycle
Hence Carnot = Carnot Cycle Eff. given by
A B
and
Carnot = TH TL(sBsA)/TH(sBsA)
Carnot = 1 TL/TH
If sink is kept at constant Temp (TL),upper temperature (TH) must be made
as high as possible to get the
maximum
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THE CARNOT VAPOR CYCLE
T-s diagram of two Carnot vapor cycles.
The Carnot cycle is the most efficient cycle operating between two specified temperature
limits but it is not a suitable model for power cycles. Because:
Process 1-2 Limiting the heat transfer processes to two-phase systems severely limits the
maximum temperature that can be used in the cycle (374C for water)
Process 2-3 The turbine cannot handle steam with a high moisture content because of the
impingement of liquid droplets on the turbine blades causing erosion and wear.
Process 4-1 It is not practical to design a pump that handles two phases.
The cycle in (b) is not suitable since it requires isentropic compression to
extremely high pressures and isothermal heat transfer at variable pressures.
1-2 isothermal heat
addition in a boiler
2-3 isentropic expansion
in a turbine
3-4 isothermal heat
rejection in a condenser
4-1 isentropic
compression in a pump
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RANKINE CYCLE: THE IDEAL CYCLE
FOR VAPOR POWER CYCLESMany of the impracticalities associated with the Carnot cycle can be eliminated
by superheating the steam in the boiler and condensing it completely in the
condenser. The cycle that results is the Rankine cycle, which is the ideal cycle
for vapor power plants. The ideal Rankine cycle does not involve any internal
irreversibilities.
The simple ideal Rankine cycle.
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Area: 3-a-b-2-c-3 representsheat transfer to the working
fluid in bioler per unit mass
flowing.
Area: 4-a-b-1-4 representsheat transfer from the
working fluid in condenser
per unit mass flowing.
Enclosed Area: 3-4-1-2-c-3
represents the net heat inputor equivalently , the net work
out put per unit of mass
flowing.
RANKINE CYCLE: THE IDEAL CYCLE
FOR VAPOR POWER CYCLES
ab
c
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10Corrosion of Steam turbine blades due to impingement of liquid droplets