# Chapter 10 Rankine Power Cycle

Document Sample

```					Chapter 10: Rankine Power Cycle

1
Looking at the cycle process

• Put a slide here that shows Carnot
cycle with cycle inside. Show Qh, Ql,
and Wnet divided into Win and Wout.
Vapor Power Cycles

• We’ll look specifically at the Rankine
cycle, which is a vapor power cycle.

• It is the primary electrical producing
cycle in the world.

• The cycle can use a variety of fuels.

3
4
5
6
We’ll simplify the power plant

3
BOILER
TURBINE        wout
qin

2                         4

CONDENSER

qout
1
win            PUMP
7
Ideal power plant cycle is called
the Rankine Cycle

compression in the pump
• 2-3 constant pressure heat addition in the
boiler.
expansion through turbine
• 4-1 constant pressure heat rejection in the
condenser
8
Rankine cycle power plant

• The steady-state first law applied to open
systems will be used to analyze the four
major components of a power plant
– Pump
– Boiler (heat exchanger)
– Turbine
– Condenser (heat-exchanger)
• The second law will be needed to evaluate
turbine performance
9
Vapor-cycle power plants

T

3
qin

wout
2

win   1   qout   4

s      10

• Typical assumptions…
– Steady flow in all components
– Steady state in all components
– Usually ignore kinetic and potential
energy changes in all components
– Pressure losses are considered
negligible in boiler and condenser
– Power components are isentropic for
ideal cycle
11
Start our analysis with the pump

0  Qpump  WPump  m(h1  h 2  KE  PE)

The pump is adiabatic, with no kinetic or
potential energy changes. The work per
unit mass is:

w pum p  h1  h 2  ( p1  p 2 )
12
Pump Analysis

This expression gives us negative value
for wp. It is standard practice in dealing
with cycles to express works as positive
values, then add or subtract depending
on whether they’re in or out.

w Pump  h1  h 2
This gives us a positive value for work.
13
Boiler is the next component.

          
0  Q boiler  Wboiler  m[h 2  h 3  KE  PE ]


•Boilers do no work. In boilers, heat
is added to the working fluid, so the
heat transfer term is already positive.
•So

Q boiler
 q boiler  h 3  h 2
m
14
Proceeding to the Turbine

           
0  Q turbine  Wturbine  m[h 3  h 4  KE  PE ]

Turbines are almost always adiabatic. In
addition, we’ll usually ignore kinetic and
potential energy changes:


Wturbine
 w  h3  h4

m
15
Last component is the Condenser

        
0  Q cond  Wcond  m[h 4  h1  KE  PE ]

Condensers do no work (they are heat
exchangers),and if there is no KE
and PE,

Q cond
 q cond  h1  h 4

m
16
More condenser...

What is the sign of qcond ?

As with work, we’re going to want
the sign of all the heat transfer
terms positive.

Q cond
 q cond  h1  h 4

m
17
Ideal Rankine Cycle

• The pump work, because it is reversible

2
wP   vdp  h2  h1
1
• and

wP  v( P2  P )
1

18
Ideal Rankine Cycle on a p-v
diagram

P

p=c
2            3

s=c               s=c

1
p=c       4

19
v
Efficiency

w out

q in

h 3 - h 4 - v(P2 - P1 )

h3 - h2

20
Example Problem

A Rankine cycle has an exhaust
pressure from the turbine of 10 kPa.
Determine the quality of the steam
leaving the turbine and the thermal
efficiency of the cycle which has
turbine inlet pressure of 15 MPa and
600C.

21
cycle problems
• Get the BIG picture first - where’s the
work, where’s the heat transfer, etc.
the data you will need in one place.
• You will need to know how to look up
properties in the tables!

22
Draw diagram of cycle

T
T3 = 600oC

P= 15 MPa         3

2
P = 10 kPa

1                 4

23
s
Put together property data

State     T (C)   P(kPa)   v(m3/kg) h(kJ/kg) s(kJ/kgK)   x

1                 10

2                15000

3        600     15000

4                 10

24
Some general characteristics of the
Rankine cycle
• Low condensing pressure (below
atmospheric pressure)
• High vapor temperature entering the
turbine (600 to 1000C)

25
Example 10-2

Find (a) thermal efficiency of cycle and (b) net power output of
plan for a mass flow rate of 15 kg/sec.
Put together property data
State   T (C)   P(kPa)   v(m3/kg) h(kJ/kg) s(kJ/kgK)   x

1

2

2s

3

4

5

6

6s
27

```
DOCUMENT INFO
Shared By:
Categories:
Stats:
 views: 10 posted: 9/8/2010 language: English pages: 27