Short Notes: Turbomachinery | Short Notes for Mechanical Engineering PDF Download

 Page 1


Turbomachinery
Turbomachine is defined as a device in which energy transfer takes place between 
a flowing fluid and a rotating element resulting in a change of pressure and 
momentum of the fluid. Energy is transferred into or out of the turbomachine 
mechanically by means of input/output shafts.
Principal Parts of a Turbo Machine
• Rotating element consisting of a rotor on which are mounted blades.
• A stationary element in the form of guide blades, nozzles, etc.
• Input/output shafts.
• Housing
Inlet
Schematic cross sectional view of a steam turbine showing the principal parts of a 
turbo machine.
Functions:
1. The rotor functions to absorb/deliver energy to the flowing fluid.
Page 2


Turbomachinery
Turbomachine is defined as a device in which energy transfer takes place between 
a flowing fluid and a rotating element resulting in a change of pressure and 
momentum of the fluid. Energy is transferred into or out of the turbomachine 
mechanically by means of input/output shafts.
Principal Parts of a Turbo Machine
• Rotating element consisting of a rotor on which are mounted blades.
• A stationary element in the form of guide blades, nozzles, etc.
• Input/output shafts.
• Housing
Inlet
Schematic cross sectional view of a steam turbine showing the principal parts of a 
turbo machine.
Functions:
1. The rotor functions to absorb/deliver energy to the flowing fluid.
2. The stator is a stationary element which may be of many types:­
° Guide blades which function to direct the flowing fluid in such a way that 
energy transfer is maximized.
o Nozzles which function to convert pressure energy of the fluid to kinetic 
energy
° Diffusers which function to convert kinetic energy to pressure energy of 
the fluid.
3. The input /output shafts function to deliver/receive mechanical energy to or 
from the machine.
4. The housing is a protective enclosure which also functions to provide a path 
of flowing fluid. While a rotor & input /output shaft are essential parts of all 
turbo machines, the stator & the housing are optional.
Classification of Turbo Machines:
1. According to the nature of energy transfer:
o Power generating turbo machines: In this, energy is transferred from the 
flowing fluid to the rotor. Hence, enthalpy of the flowing fluid decreases 
as it flows across. There is a need for an output shaft.
° Ex: Hydraulic turbines such as Francis turbine, Pelton wheel turbine, 
Kaplan turbine, steam turbine such as De-Laval turbine, Parsons Turbine 
etc, Gas turbines etc,
° Power absorbing Turbo machines: In this, energy is transferred from the 
rotor to the flowing fluid. The enthalpy of the fluid increases as it flows 
there is a need for an input shaft.
° Ex: Centrifugal pump, Compressor, blower, fan etc,
° Power transmitting turbo machines: In this energy is transferred from 
one rotor to another by means of a flowing fluid. There is a need for an 
input / output shafts. The transfer of energy occurs due to fluid action.
° Ex: Hydraulic coupling, torque converter etc,
Schematic representation of different types of turbomachine based on fluid flow:
• Axial flow fan.
• Radial outward flow fan.
• Mixed flow hydraulic turbine.
2. Based on the type of fluid flow:
° Tangential flow in which fluid flows tangential to the rotor Ex: Pelton 
wheel etc,
° Axial flow in which the fluid flows more or less parallel to the axes of the 
shafts /rotors. Ex: Kaplan turbine, Axial flow compressor.
° Radial flow in which fluid flows along the radius of the rotor this is again 
classified as:
¦ Radially inward flow. Ex: Old fancies turbine.
¦ Radially outward flow. Ex: Centrifugal Pump
° Mixed flow which involves radius entry & axial exit or vise-versa. Ex: 
Modem francises turbine & Centrifugal Pump
3. Based on the type of Head:
o High head &low discharge .Ex: Pelton wheel.
° Medium head &medium discharge. Ex: Francis turbine.
° Low head & high discharge. Ex: Kaplan turbine.
Page 3


Turbomachinery
Turbomachine is defined as a device in which energy transfer takes place between 
a flowing fluid and a rotating element resulting in a change of pressure and 
momentum of the fluid. Energy is transferred into or out of the turbomachine 
mechanically by means of input/output shafts.
Principal Parts of a Turbo Machine
• Rotating element consisting of a rotor on which are mounted blades.
• A stationary element in the form of guide blades, nozzles, etc.
• Input/output shafts.
• Housing
Inlet
Schematic cross sectional view of a steam turbine showing the principal parts of a 
turbo machine.
Functions:
1. The rotor functions to absorb/deliver energy to the flowing fluid.
2. The stator is a stationary element which may be of many types:­
° Guide blades which function to direct the flowing fluid in such a way that 
energy transfer is maximized.
o Nozzles which function to convert pressure energy of the fluid to kinetic 
energy
° Diffusers which function to convert kinetic energy to pressure energy of 
the fluid.
3. The input /output shafts function to deliver/receive mechanical energy to or 
from the machine.
4. The housing is a protective enclosure which also functions to provide a path 
of flowing fluid. While a rotor & input /output shaft are essential parts of all 
turbo machines, the stator & the housing are optional.
Classification of Turbo Machines:
1. According to the nature of energy transfer:
o Power generating turbo machines: In this, energy is transferred from the 
flowing fluid to the rotor. Hence, enthalpy of the flowing fluid decreases 
as it flows across. There is a need for an output shaft.
° Ex: Hydraulic turbines such as Francis turbine, Pelton wheel turbine, 
Kaplan turbine, steam turbine such as De-Laval turbine, Parsons Turbine 
etc, Gas turbines etc,
° Power absorbing Turbo machines: In this, energy is transferred from the 
rotor to the flowing fluid. The enthalpy of the fluid increases as it flows 
there is a need for an input shaft.
° Ex: Centrifugal pump, Compressor, blower, fan etc,
° Power transmitting turbo machines: In this energy is transferred from 
one rotor to another by means of a flowing fluid. There is a need for an 
input / output shafts. The transfer of energy occurs due to fluid action.
° Ex: Hydraulic coupling, torque converter etc,
Schematic representation of different types of turbomachine based on fluid flow:
• Axial flow fan.
• Radial outward flow fan.
• Mixed flow hydraulic turbine.
2. Based on the type of fluid flow:
° Tangential flow in which fluid flows tangential to the rotor Ex: Pelton 
wheel etc,
° Axial flow in which the fluid flows more or less parallel to the axes of the 
shafts /rotors. Ex: Kaplan turbine, Axial flow compressor.
° Radial flow in which fluid flows along the radius of the rotor this is again 
classified as:
¦ Radially inward flow. Ex: Old fancies turbine.
¦ Radially outward flow. Ex: Centrifugal Pump
° Mixed flow which involves radius entry & axial exit or vise-versa. Ex: 
Modem francises turbine & Centrifugal Pump
3. Based on the type of Head:
o High head &low discharge .Ex: Pelton wheel.
° Medium head &medium discharge. Ex: Francis turbine.
° Low head & high discharge. Ex: Kaplan turbine.
Application of 1st & 2n d law of thermodynamics of turbo machines:
In a turbo machine, the fluctuations in the properties when observed over a period 
of time are found to be negligible. Hence, a turbo machine may be treated as a 
steady flow machine with reasonable accuracy & hence, we may apply the steady 
flow energy equation for the analysis of turbo machine.
Hence we may write
Where, subscript T is at the point of entry & subscript '2' is at point of exit.
It is also true that, thermal losses are minimal compared to the amount of work 
transferred & hence may be neglected. Hence we may write,
-\v = (hC j - h „ )
Where, h02 & hoi are stagnation exit & entry respectively, 
w = Ah0.
In a power generating turbo machine, Ah0 is negative (since h02 < hoi) & hence w is 
positive.
On the same line, for a power absorbing turbo machine, Ah0 is positive (since h02 > 
h0i) & hence w is negative.
From the 2n d law of Thermodynamics:
Tds = dh— vdp 
— d\v = vdp -i-Tds
w — — I vdp — j T ds
In the above relation, we note that vdp would be a negative quantity for a power 
generating turbo machine & positive for power absorbing turbo machine.
Hence Tds which is always a positive quantity would reduce the amount of work 
generated in the former case & increase the work absorbed in the later case. 
Efficiency of a turbo machine:
Generally, we define 2 types of turbo machine .in case of turbo machine to account 
for various losses 2 type of efficiency is considered:
• Hydraulic efficiency/isentropic efficiency
• Mechanical efficiency.
1. Hydraulic efficiency/isentropic efficiency:
To account for the energy loss between the fluid & the rotor
q -w = (h , — h ;)- !-
v ; - v
-he(zi - z I)
(n
(n ^
‘ i s s i tpspsr*i a& iofbr * c j e hire
J C r l O T
2. Mechanical efficiency:
Page 4


Turbomachinery
Turbomachine is defined as a device in which energy transfer takes place between 
a flowing fluid and a rotating element resulting in a change of pressure and 
momentum of the fluid. Energy is transferred into or out of the turbomachine 
mechanically by means of input/output shafts.
Principal Parts of a Turbo Machine
• Rotating element consisting of a rotor on which are mounted blades.
• A stationary element in the form of guide blades, nozzles, etc.
• Input/output shafts.
• Housing
Inlet
Schematic cross sectional view of a steam turbine showing the principal parts of a 
turbo machine.
Functions:
1. The rotor functions to absorb/deliver energy to the flowing fluid.
2. The stator is a stationary element which may be of many types:­
° Guide blades which function to direct the flowing fluid in such a way that 
energy transfer is maximized.
o Nozzles which function to convert pressure energy of the fluid to kinetic 
energy
° Diffusers which function to convert kinetic energy to pressure energy of 
the fluid.
3. The input /output shafts function to deliver/receive mechanical energy to or 
from the machine.
4. The housing is a protective enclosure which also functions to provide a path 
of flowing fluid. While a rotor & input /output shaft are essential parts of all 
turbo machines, the stator & the housing are optional.
Classification of Turbo Machines:
1. According to the nature of energy transfer:
o Power generating turbo machines: In this, energy is transferred from the 
flowing fluid to the rotor. Hence, enthalpy of the flowing fluid decreases 
as it flows across. There is a need for an output shaft.
° Ex: Hydraulic turbines such as Francis turbine, Pelton wheel turbine, 
Kaplan turbine, steam turbine such as De-Laval turbine, Parsons Turbine 
etc, Gas turbines etc,
° Power absorbing Turbo machines: In this, energy is transferred from the 
rotor to the flowing fluid. The enthalpy of the fluid increases as it flows 
there is a need for an input shaft.
° Ex: Centrifugal pump, Compressor, blower, fan etc,
° Power transmitting turbo machines: In this energy is transferred from 
one rotor to another by means of a flowing fluid. There is a need for an 
input / output shafts. The transfer of energy occurs due to fluid action.
° Ex: Hydraulic coupling, torque converter etc,
Schematic representation of different types of turbomachine based on fluid flow:
• Axial flow fan.
• Radial outward flow fan.
• Mixed flow hydraulic turbine.
2. Based on the type of fluid flow:
° Tangential flow in which fluid flows tangential to the rotor Ex: Pelton 
wheel etc,
° Axial flow in which the fluid flows more or less parallel to the axes of the 
shafts /rotors. Ex: Kaplan turbine, Axial flow compressor.
° Radial flow in which fluid flows along the radius of the rotor this is again 
classified as:
¦ Radially inward flow. Ex: Old fancies turbine.
¦ Radially outward flow. Ex: Centrifugal Pump
° Mixed flow which involves radius entry & axial exit or vise-versa. Ex: 
Modem francises turbine & Centrifugal Pump
3. Based on the type of Head:
o High head &low discharge .Ex: Pelton wheel.
° Medium head &medium discharge. Ex: Francis turbine.
° Low head & high discharge. Ex: Kaplan turbine.
Application of 1st & 2n d law of thermodynamics of turbo machines:
In a turbo machine, the fluctuations in the properties when observed over a period 
of time are found to be negligible. Hence, a turbo machine may be treated as a 
steady flow machine with reasonable accuracy & hence, we may apply the steady 
flow energy equation for the analysis of turbo machine.
Hence we may write
Where, subscript T is at the point of entry & subscript '2' is at point of exit.
It is also true that, thermal losses are minimal compared to the amount of work 
transferred & hence may be neglected. Hence we may write,
-\v = (hC j - h „ )
Where, h02 & hoi are stagnation exit & entry respectively, 
w = Ah0.
In a power generating turbo machine, Ah0 is negative (since h02 < hoi) & hence w is 
positive.
On the same line, for a power absorbing turbo machine, Ah0 is positive (since h02 > 
h0i) & hence w is negative.
From the 2n d law of Thermodynamics:
Tds = dh— vdp 
— d\v = vdp -i-Tds
w — — I vdp — j T ds
In the above relation, we note that vdp would be a negative quantity for a power 
generating turbo machine & positive for power absorbing turbo machine.
Hence Tds which is always a positive quantity would reduce the amount of work 
generated in the former case & increase the work absorbed in the later case. 
Efficiency of a turbo machine:
Generally, we define 2 types of turbo machine .in case of turbo machine to account 
for various losses 2 type of efficiency is considered:
• Hydraulic efficiency/isentropic efficiency
• Mechanical efficiency.
1. Hydraulic efficiency/isentropic efficiency:
To account for the energy loss between the fluid & the rotor
q -w = (h , — h ;)- !-
v ; - v
-he(zi - z I)
(n
(n ^
‘ i s s i tpspsr*i a& iofbr * c j e hire
J C r l O T
2. Mechanical efficiency:
( )i p s ’r i r <1 :'_ » . l : r . J
_ ' V*
w
( . v-»r . i i : ^
Wn- — r e t c r
w
1 r f :
Schematic representation of Compression & Expansion process: 
(a) Power absorbing machine, (b) Power generating machine.
(1) Power generating machine 
^ ki = h;i —
^,-j = h0 1 —ho:
w ~ = K - K >
w . 5 = h1- h 1 ,
w
fh-l —
w .
hpi ho ;
h0 i h0 .
_ _ h „ - h m
w.
V t. t =
»?,_ =
Wact h., — h.,
_________________ ___ C l__________ v l
W s - t hj - h 0 ,
Wi;: _ h;i - h;; 
w “ _ h, — hi
(2). Powerabsorbing turbomachine: 
~ h0, — hsl
W. = W,
= h « " h „
WM = h ^ -h , 
W _ ,= h i- h M 
w „ = h i - h t
* -
w .
Wact
hI: ~ hc.
ho: — h0 1
J7.-s =
_ ¦ h V .-h ,
W.
hoi-hj
=
W s - t _ h1 , —h E 1 
Wact hc, — h0 1
_ Wc: h‘ a —h.
\V
h 0 2 hQ 1
Analysis of Energy Transfer in turbo machines: Analysis of energy transfer in turbo 
machines requires a consideration of the kinematics and dynamic factors involved. 
The factors include changes in the fluid velocity, rotor velocity and the forces 
caused due to change in the velocity.
We apply Newton’s second law of motion as applicable to rotary movement, i.e., 
Torque is proportional to the rate of change of angular momentum.
j _ d(rnVr)
dt
Page 5


Turbomachinery
Turbomachine is defined as a device in which energy transfer takes place between 
a flowing fluid and a rotating element resulting in a change of pressure and 
momentum of the fluid. Energy is transferred into or out of the turbomachine 
mechanically by means of input/output shafts.
Principal Parts of a Turbo Machine
• Rotating element consisting of a rotor on which are mounted blades.
• A stationary element in the form of guide blades, nozzles, etc.
• Input/output shafts.
• Housing
Inlet
Schematic cross sectional view of a steam turbine showing the principal parts of a 
turbo machine.
Functions:
1. The rotor functions to absorb/deliver energy to the flowing fluid.
2. The stator is a stationary element which may be of many types:­
° Guide blades which function to direct the flowing fluid in such a way that 
energy transfer is maximized.
o Nozzles which function to convert pressure energy of the fluid to kinetic 
energy
° Diffusers which function to convert kinetic energy to pressure energy of 
the fluid.
3. The input /output shafts function to deliver/receive mechanical energy to or 
from the machine.
4. The housing is a protective enclosure which also functions to provide a path 
of flowing fluid. While a rotor & input /output shaft are essential parts of all 
turbo machines, the stator & the housing are optional.
Classification of Turbo Machines:
1. According to the nature of energy transfer:
o Power generating turbo machines: In this, energy is transferred from the 
flowing fluid to the rotor. Hence, enthalpy of the flowing fluid decreases 
as it flows across. There is a need for an output shaft.
° Ex: Hydraulic turbines such as Francis turbine, Pelton wheel turbine, 
Kaplan turbine, steam turbine such as De-Laval turbine, Parsons Turbine 
etc, Gas turbines etc,
° Power absorbing Turbo machines: In this, energy is transferred from the 
rotor to the flowing fluid. The enthalpy of the fluid increases as it flows 
there is a need for an input shaft.
° Ex: Centrifugal pump, Compressor, blower, fan etc,
° Power transmitting turbo machines: In this energy is transferred from 
one rotor to another by means of a flowing fluid. There is a need for an 
input / output shafts. The transfer of energy occurs due to fluid action.
° Ex: Hydraulic coupling, torque converter etc,
Schematic representation of different types of turbomachine based on fluid flow:
• Axial flow fan.
• Radial outward flow fan.
• Mixed flow hydraulic turbine.
2. Based on the type of fluid flow:
° Tangential flow in which fluid flows tangential to the rotor Ex: Pelton 
wheel etc,
° Axial flow in which the fluid flows more or less parallel to the axes of the 
shafts /rotors. Ex: Kaplan turbine, Axial flow compressor.
° Radial flow in which fluid flows along the radius of the rotor this is again 
classified as:
¦ Radially inward flow. Ex: Old fancies turbine.
¦ Radially outward flow. Ex: Centrifugal Pump
° Mixed flow which involves radius entry & axial exit or vise-versa. Ex: 
Modem francises turbine & Centrifugal Pump
3. Based on the type of Head:
o High head &low discharge .Ex: Pelton wheel.
° Medium head &medium discharge. Ex: Francis turbine.
° Low head & high discharge. Ex: Kaplan turbine.
Application of 1st & 2n d law of thermodynamics of turbo machines:
In a turbo machine, the fluctuations in the properties when observed over a period 
of time are found to be negligible. Hence, a turbo machine may be treated as a 
steady flow machine with reasonable accuracy & hence, we may apply the steady 
flow energy equation for the analysis of turbo machine.
Hence we may write
Where, subscript T is at the point of entry & subscript '2' is at point of exit.
It is also true that, thermal losses are minimal compared to the amount of work 
transferred & hence may be neglected. Hence we may write,
-\v = (hC j - h „ )
Where, h02 & hoi are stagnation exit & entry respectively, 
w = Ah0.
In a power generating turbo machine, Ah0 is negative (since h02 < hoi) & hence w is 
positive.
On the same line, for a power absorbing turbo machine, Ah0 is positive (since h02 > 
h0i) & hence w is negative.
From the 2n d law of Thermodynamics:
Tds = dh— vdp 
— d\v = vdp -i-Tds
w — — I vdp — j T ds
In the above relation, we note that vdp would be a negative quantity for a power 
generating turbo machine & positive for power absorbing turbo machine.
Hence Tds which is always a positive quantity would reduce the amount of work 
generated in the former case & increase the work absorbed in the later case. 
Efficiency of a turbo machine:
Generally, we define 2 types of turbo machine .in case of turbo machine to account 
for various losses 2 type of efficiency is considered:
• Hydraulic efficiency/isentropic efficiency
• Mechanical efficiency.
1. Hydraulic efficiency/isentropic efficiency:
To account for the energy loss between the fluid & the rotor
q -w = (h , — h ;)- !-
v ; - v
-he(zi - z I)
(n
(n ^
‘ i s s i tpspsr*i a& iofbr * c j e hire
J C r l O T
2. Mechanical efficiency:
( )i p s ’r i r <1 :'_ » . l : r . J
_ ' V*
w
( . v-»r . i i : ^
Wn- — r e t c r
w
1 r f :
Schematic representation of Compression & Expansion process: 
(a) Power absorbing machine, (b) Power generating machine.
(1) Power generating machine 
^ ki = h;i —
^,-j = h0 1 —ho:
w ~ = K - K >
w . 5 = h1- h 1 ,
w
fh-l —
w .
hpi ho ;
h0 i h0 .
_ _ h „ - h m
w.
V t. t =
»?,_ =
Wact h., — h.,
_________________ ___ C l__________ v l
W s - t hj - h 0 ,
Wi;: _ h;i - h;; 
w “ _ h, — hi
(2). Powerabsorbing turbomachine: 
~ h0, — hsl
W. = W,
= h « " h „
WM = h ^ -h , 
W _ ,= h i- h M 
w „ = h i - h t
* -
w .
Wact
hI: ~ hc.
ho: — h0 1
J7.-s =
_ ¦ h V .-h ,
W.
hoi-hj
=
W s - t _ h1 , —h E 1 
Wact hc, — h0 1
_ Wc: h‘ a —h.
\V
h 0 2 hQ 1
Analysis of Energy Transfer in turbo machines: Analysis of energy transfer in turbo 
machines requires a consideration of the kinematics and dynamic factors involved. 
The factors include changes in the fluid velocity, rotor velocity and the forces 
caused due to change in the velocity.
We apply Newton’s second law of motion as applicable to rotary movement, i.e., 
Torque is proportional to the rate of change of angular momentum.
j _ d(rnVr)
dt
Another important consideration is the treatment of a turbo machine as a steady 
flow machine.
1. This involves following assumptions:
2. Mass-flow rate is constant.
3. State of fluid at any given point does not change.
4. Heat and Work transfer are constant.
5. Leakage losses are negligible.
6. Same steady mass of fluid flows through all section.
Velocity Components:
The fluid enters the rotor with an absolute velocity say Vi and leaves with an 
absolute velocity say V2.
The absolute velocity of the fluid will have components in the axial, radial and 
tangential direction which may be referred to as Va,Vw and Vf respectively.
The axial components do not participate in the energy transfer but cause a thrust 
which is borne by the thrust bearings. The radial components also do not 
participate in the energy transfer but cause a thrust which are borne by the journal 
bearings. The only components which participate in the energy transfer is the 
tangential component Vw.
Vai and Va2 : Axial components of Vi and V2 respectively.
Vfi and Vf2 : Radial components of Vi and V2 respectively.
Vwi and Vw2: Tangential components of Vi and V2 respectively referred to as whirl 
velocity, flow velocity. Let the rotor move with an angular velocity cj.
Velocity Triangles:
These are formed at the inlet and exit by the combination of rotor velocity of a fluid 
V, and relative velocity Vr which is the vectorial difference of V and U.
Derivation of Euler’s Turbine equation:
By Newton’s second law, Torque on the turbo machine