Turbomachine Module03.pptx

1
Approved by AICTE |Affiliated to VTU | Recognized by UGC with 2(f) & 12(B) status |Accredited by NBA and NAAC
An Autonomous Institution
Affiliated to VTU, Belagavi,
Approved by AICTE, New Delhi,
Recognised by UGC with 2(f) & 12 ( B)
Accredited by NBA & NAAC
Turbomachines (18ME54)
MODULE 3
Steam Turbine
Presented by : Shweta Agrawal

2
Approved by AICTE |Affiliated to VTU | Recognized by UGC with 2(f) & 12(B) status |Accredited by NBA and NAAC 2
Content

3
Content

4
Content

5
Approved by AICTE |Affiliated to VTU | Recognized by UGC with 2(f) & 12(B) status |Accredited by NBA and NAAC
Content
•Steam Turbines:
•Classification, Single stage impulse turbine
•condition for maximum blade efficiency
•stage efficiency, Need and methods of compounding
•Multi-stage impulse turbine, expression for maximum utilization factor
•Numerical Problems
•Reaction turbine – Parsons’s turbine
• condition for maximum utilization factor reaction staging
•Numerical Problems

6
Recalling of earlier concept

7
Bridge material –Rankine Cycle
•The Rankine cycle closely describes the process by
which steam-operated heat engines commonly found
in thermal power generation plants generate power.
•Power depends on the temperature difference
between a heat source and a cold source. The higher
the difference, the more mechanical power can be
efficiently extracted out of heat energy.
•The efficiency of the Rankine cycle is limited by the
high heat of vaporization of the working fluid. Also,
unless the pressure and temperature reach super
critical levels in the steam boiler, the temperature
range the cycle can operate over is quite small: steam
turbine entry temperatures are typically around 565 °C
and steam condenser temperatures are around 30 °C.

8
Steam Turbine
•Steam turbines use the steam as a working fluid. In steam turbines, high pressure steam from the boiler
is expanded in nozzle, in which the enthalpy of steam being converted into kinetic energy
•Thus, the steam at high velocity at the exit of nozzle impinges over the moving blades (rotor) which cause
to change the flow direction of steam and thus cause a tangential force on the rotor blades
•Due to this dynamic action between the rotor and the steam, thus the work is developed. These
machines may be of axial or radial flow type devices. Steam turbines may be of two kinds, namely,
(i) Impulse turbine and
(ii) Reaction turbine

9
Impulse and Reaction Turbine
In Impulse turbine, the whole enthalpy drop (pressure drop) occurs in the nozzle itself. Hence pressure
remains constant when the fluids pass over the rotor blades. Fig.1 shows the schematic diagram of Impulse
turbine.
In Reaction turbines, in addition to the pressure drop in the nozzle there will also be pressure drop occur when
the fluid passes over the rotor blades. Most of the steam turbine is of axial flow type devices except
Ljungstrom turbine which is a radial type.

10
Compounding of Steam Turbines
In one stage due to high rotational speed all the available energy at inlet of machine is not utilized
which being simply wasted at exit of machine. Also for maximum utilization, exit velocity of steam
should be minimum or negligible.
Hence, for better utilization, one has to have a reasonable tangential speed of rotor. In order to
achieve this, we have to use, two or more rows of moving blades with a row of stationary blades
between every pair of them. Now, the total energy of steam available at inlet of machine can be
absorbed by all the rows in succession until the kinetic energy of steam at the end of the last row
becomes negligible.
Hence Compounding can be defined "as the method of obtaining reasonable tangential speed of
rotor for a given overall pressure drop by using more than one stage"

11
Compounding can be done by the following methods
(i) Velocity compounding,
(ii) Pressure compounding or Rateau stage
(iii) Pressure-Velocity compounding and
(iv) Impulse- Reaction staging.
1. Velocity Compounding (Curtis Stage) of Impulse Turbine :
This consists of set of nozzles, rows of moving blades (rotor) &a row of stationary blades (stator).
The function of stationary blades is to direct the steam coming from the first moving row to the next
moving row without appreciable change in velocity. All the kinetic energy available at the nozzle exit is
successively absorbed by all the moving rows & the steam is sent from the last moving row with low
velocity to achieve high utilization. The turbine works under this type of compounding stage is called
velocity compounded turbine. Example Curtis stage steam turbine

12
2. Pressure Compounded (Rateau Stage ) Impulse Turbine :
A number of simple impulse stages arranged in series is called as pressure compounding. In this case, the
turbine is provided with rows of fixed blades which act as a nozzle at the entry of each rows of moving
blades.
The total pressure drop of steam does not take place in a single nozzle but divided among all the rows of
fixed blades which act as nozzle for the next moving rows.
Pressure compounding leads to higher efficiencies because very high flow velocities are avoided through
the use of purely convergent nozzles. For maximum utilization, the absolute velocity of steam at the
outlet of the last rotor must be axially directed.
It is usual in large turbines to have pressure compounded or reaction stages after the velocity
compounded stage.

13

14
3. Pressure -Velocity Compounding:
In this method, high rotor speeds are reduced without sacrificing the efficiency or the output.
Pressure drop from the chest pressure to the condenser pressure occurs at two stages. This type of
arrangement is very popular due to simple construction as compared to pressure compounding
steam turbine.
First and second stage taken separately are identical to a velocity compounding consists of a set of
nozzles and rows of moving blades fixed to the shaft and rows of fixed blades to casing. The entire
expansion takes place in the nozzles.
The high velocity steam parts with only portion of the kinetic energy in the first set of the moving
blades and then passed on to fixed blades where only change in direction of jet takes place without
appreciable loss in velocity. This jet then passes on to another set of moving vanes where further
drop in kinetic energy occurs.
This type of turbine is also called Curtis Turbine.

15
4. Impulse- Reaction Turbine:
In this type of turbine there is application of both principles namely impulse and reaction.
This type of turbine is shown in Fig.6. The fixed blades in this arrangement corresponding to the
nozzles referred in the impulse turbine. Instead of a set of nozzles, steam is admitted for whole
of the circumference. In passing through the first row of fixed blades, the steam undergoes a
small drop in pressure and its velocity increases. Steam then enters the first row of moving
blades as the case in impulse turbine it suffers a change in direction and therefore momentum.
This gives an impulse to the blades. The pressure drop during this gives rise to reaction in the
direction opposite to that of added velocity. Thus the driving force is vector summation of
impulse and reaction.
Normally this turbine is known as Reaction turbine. The steam velocity in this typeof turbine is
comparatively low, the maximum being about equal to blade velocity. This type of turbine is very
successful in practice. It is also called as Parson's Reaction turbine

16

17
Condition for Maximum Utilization Factor or Blade efficiency with
Equiangular Blades for Impulse Turbine
Condition for maximum utilization factor or blade efficiency with equiangular
blades for Impulse turbine and the influence of blade efficiency on the steam
speed in a single stage Impulse turbine can be obtained by considering
corresponding velocity diagrams as shown in Figure.
Due to the effect of blade friction loss, the relative velocity at outlet is reduced
than the relative velocity at inlet. Therefore,Vr2 = CbVr1 , corresponding to this
condition, velocity triangles (qualitative only) are drawn as shown in figure.

18
Condition for Maximum Utilization Factor or Blade efficiency with
Equiangular Blades for Impulse Turbine

19

20

21
Condition of Maximum Efficiency for Velocity Compounded
Impulse Turbine (Curtis Turbine)

22
The velocity triangles for first stage and second stage of a Curtis turbine are as shown In above figure.
The speed and the angles should be so selected that the final absolute velocity of steam leaving the
second row is axial, so as to obtain maximum efficiency. The tangential speed of blade for both the
rows is same since all the moving blades are mounted on the same shaft.
In the first row of moving blades, the work done per kg of steam is, W1 =U (Vu1 +Vu2)/gc =UVu1/gc
From I stage velocity triangle, we get, W1 =U (Vr1cosβ +Vr2cos)/g If β1= β2 and Vr1 = Vr2,
then, W1 =2U (Vr1cos β1) /g
W1=2U (V1cosα1 - U) /g
The magnitude of the absolute velocity of steam leaving the first row is same as the velocity of steam
entering the second row of moving blades, if there is no frictional loss (i.e.,V2 =V3 ) but only the
direction is going to be changed.

23
In the second moving row, work done per kg of steam is,
W2 =U Vu2 /g = U (Vr3cos β3 + Vr4cos ) /g
Again if β3= β4 and Vr3 = Vr4
W2 =2U (Vr3cos β3) /g
W2=2U (V3 cosα3 - U) /g
If no loss in absolute velocity of steam entering from I rotor to the II rotor, then V3= V2 & α3 =
α2
W2=2U (V2 cosα2 - U) /g
Also, V2 cosα2 = Vr2cos β2-U= Vr1cosβ1 - U. (Vr1 = Vr2 & β1 = β2)
V2 cosα2 = (V1 cosα2 - U) –U (Vr1cos β1 = V1 cosα1 - U)

24
V2 cosα2 = V1 cosα1 -2U
W2 = 2U (V1cos α1 - 3U) /g
Total Work done per kg of steam from both the stages is given by
WT =W1 +W2 =2U [V1 cosα1 - 3U+ V1 cosα1 - U]/g
WT =2U [2V1 cosα1- 4U]/g
WT =4U [V1 cosα1- 2U]/g
In general form, the above equation can be expressed as,
W = 2 n U [V1 cosα1 - nU]/g
Where, n = number of stages.

25
Then the blade efficiency is given by,

26
And work done in the last row =1/2n of total work
V1 =Absolute velocity of steam entering the first rotor or steam
velocity at the exit of the nozzle, m/s.
α1= Nozzle angle with respect to wheel plane or tangential
blade speed at inlet to the first rotor, degrees.
Vr1 = Relative velocity of fluid at inlet of I stage, m/s.
β1= Rotor or blade angle at inlet of 1 rotor made byV, degree
Vr2 = Relative velocity of fluid at outlet of I stage.
β2= Rotor or blade angle at outlet of I rotor made degree
V2 =Absolute velocity of steam leaving the I rotor or stage, m/s
α2= Exit angle of steam made by V2, degree
V3 = Absolute velocity of steam entering the 2 rotor or exit
velocity of the steam from the stator m/s.
α3= Exit angle of stator for 2 rotor, degree

27
Example 1

28
Example 1

29
Example 1

30
Example 2

31
Example 2

32
Example 2

33
Example 2

34
Example 2

35
Losses in Parsons stage
For the purpose of analysis, one Parsons stage is considered as made up of two
distinct parts: Blade passages in the stator and blade passages in the rotor. (It may be
noted here that there are many Parsons stages in a turbine and the stage, now under
consideration, has a stage previous to it and a stage later). Because the expansion of
steam takes place equally in both the stator and rotor passages, it is as if there are
two sets of nozzles, first in the stator and second in the rotor. In the first part, that is,
the stator passage, the exit velocity is V1 and the inlet velocity is V2 (being the exit
velocity of the previous stage). In the second part, it is the relative velocity Vr1
increasing to Vr2. Considering the stator blade passage as the nozzle with a nozzle
efficiency Gn, we have

36

37

38

39
Parsons stage
Parsons stages of steam turbines have a degree of reaction R equal to 0.5. One
stator blade-ring followed by a rotor blade-ring together make up the one stage.
The blades are designed so that the passages between the blades act like nozzles
in both the stator and rotor. The expansion of steam takes place in both the rings.
The areas of flow have to be increased continuously to accommodate the
increased volume flow rates. The velocity triangles at the inlet and outlet of every
rotor blade ring become symmetrical. The usual practice is to have the same
geometry (@1, @2, A1, A2) of the blades with continuously increasing heights.
The same set of velocity triangles and analysis hold good for a few of the rotor
rings in succession. When the increase in the height of blades becomes limited
after a few rings, the mean diameter of rotor rings can be increased so that
another set of velocity triangles and analysis can hold good for another series of
rotor rings

40
Example 3

41
Example 3

42
Example 3

43
Example 3

44

45
Example 4

46
Example 4

47
Example 4

48
Comprehensive question- MCQs
1. Steam turbine is clas sified on basis of __________
a) type of blades
b) exhausting condition
c) type of Steam flow
d) all of the mentioned
2. Impulse blades are in the shape of __________
a) Rain drop
b) Circular
c) Half moon
d) None of the mentioned
3. When steam reaches turbine blades the type of force responsible for moving turbine blades are
_____________
a) Axial force
b) Shear force
c) Longitudinal force
d) None of the mentioned

49
4. Reaction turbine works with the force obtained from change in pressure energy.
a) True
b) False
5. In an impulse turbine.......
a)The steam is expanded in nozzlesonly and there is a pressure drop and heat drop
b)The steam is expanded both in fixed and moving blades continuously
c)The steam is expanded in moving blades only
d)The pressure and temperature of steam remains constant
6. The person's reaction turbine has........
a)Only moving blades
b)Only fixed blades
c)Identical moving and fixed blades
d)Fixed and moving blades of different shape
7. The stage efficiency (ηs)is given by ( where ηb=blading efficiency and ηn =nozzle efficiency )........
a)ηb/ηn
b)ηn/ηb
c)ηbηn
d)ηn/ηb

50
8. The thermal efficiency of a steam turbine is......than that of steam engine
a)Lower
b)Higher
c)Same
d)None of the above
9. The ratio of total useful heat drop to the total insentropic heat drop is called.......
a)Internal efficiency
b)Rankine efficiency
c)Stage efficiency
d)Efficiency ratio
10. The person's reaction turbine the degree of reactio is........
a)20%
b)30%
c)40%
d)50%

51
NPTEL and Innovative content Link
1. https://nptel.ac.in/content/storage2/courses/112104117/ui/Course_home-lec22.htm
2. https://nptel.ac.in/courses/112/107/112107216/
3. https://www.youtube.com/watch?v=XjtuNMllrIk
4. https://www.youtube.com/watch?v=dS3GpvIl6fc
5. https://www.youtube.com/watch?v=SPg7hOxFItI

52
VTU previous years question paper
July 2018

53
VTU previous years question paper
July 2019

54
Self assessment questions
1. Is it possible to completely shutdown or partially reduce the steam extraction from turbines to feedwater
heaters in an operating steam power plant?
2. How do wet-steam turbines control the inlet quality between stages?
3. What is the function of ‘back pressure steam turbine’?
4. What is a diaphragm?
5. What are four types of turbine seals?
6. In which turbine is tip leakage a problem?
7. What are two types of clearance in a turbine?
8. Why should a steam or moisture separator be installed in the steam line next to a steam turbine?
9. What are some conditions that may prevent a turbine from developing full power?
10. What is an extraction turbine?

55
Case Study on steam power plant
https://www.researchgate.net/publication/328742025_Perfor
mance_Analysis_of_a_Steam_Power_Plant_A_Case_Study

56
References
1. Turbomachinery by B K Venkanna
2. Turbine, Compressor and Fans by S M Yahya

57
Thank You
Shweta Agrawal
AP, ME Dept
MVJ College of Engineering
Near ITPB, Whitefield
Bangalore-560 067

Turbomachine Module03.pptx

Recommended

Recommended

More Related Content

Similar to Turbomachine Module03.pptx

Similar to Turbomachine Module03.pptx (20)

Recently uploaded

Recently uploaded (20)

Turbomachine Module03.pptx