8/10/2019 Lec 1_Ch 10

1/10

Lecture 1

Vapor Power Cycles (Ch-10)

Ideal Rankine Cycle

Thermodynamics - II

Zia Ud Din

8/10/2019 Lec 1_Ch 10

2/10

8/10/2019 Lec 1_Ch 10

3/10

Components of a Vapour Power Plant

8/10/2019 Lec 1_Ch 10

4/10

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

8/10/2019 Lec 1_Ch 10

5/10

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

8/10/2019 Lec 1_Ch 10

6/10

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

8/10/2019 Lec 1_Ch 10

7/10

7

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

8/10/2019 Lec 1_Ch 10

8/10

8

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.

8/10/2019 Lec 1_Ch 10

9/10

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

8/10/2019 Lec 1_Ch 10

10/10

10Corrosion of Steam turbine blades due to impingement of liquid droplets