Steam Turbine Classification

June 8, 2024

Anonymous
Rotary Thermodynamic devices Steam turbines & their
classifications Impulse & Reaction type Turbines,
Thermodynamics of compressible fluid-flow, equation and
continuity Isentropic flow throughnozzles, velocity diagram,
Blade 12 efficiency, optimum velocity ratio, multi-staging,
velocity & pressurecompounding, losses in turbines, erosion of
turbine blades, turbine governing, performance analysis
ofturbine, Condensing system.
VERY DETAILED NOTES FOR SEMESTER EXAM

ChatGPT
Rotary Thermodynamic Devices: Steam Turbines and Their
Classifications
Introduction to Steam Turbines
Steam turbines are rotary mechanical devices that convert thermal energy from
pressurized steam into mechanical work. They are used in various applications including
power generation, marine propulsion, and mechanical drive systems in industrial
processes.

Classifications of Steam Turbines

Steam turbines can be classified based on several criteria:

1. Based on Action of Steam on Blades:

Impulse Turbines: Steam expands entirely in the nozzles, and the high-velocity jet
impinges on the turbine blades, converting the kinetic energy of steam into
mechanical energy.

Reaction Turbines: Steam expands partially in the stationary blades (nozzles)

and partially in the moving blades. Both pressure and velocity change across the

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 blades.

2. Based on Steam Exhaust Conditions:

Condensing Turbines: Exhaust steam is condensed in a condenser, typically used

for power generation.

Non-condensing Turbines: Exhaust steam is used for industrial processes, also

known as back-pressure turbines.

3. Based on Steam Flow Direction:

Axial Flow Turbines: Steam flows parallel to the turbine shaft.

Radial Flow Turbines: Steam flows perpendicular to the turbine shaft.

4. Based on Number of Stages:

Single-Stage Turbines: Only one set of nozzles and blades.

Multi-Stage Turbines: Multiple sets of nozzles and blades, used for higher
efficiency and power.

5. Based on Pressure of Steam:

High-Pressure Turbines

Intermediate-Pressure Turbines

Low-Pressure Turbines

Impulse and Reaction Type Turbines

Impulse Turbines

Working Principle: In impulse turbines, steam is expanded in a nozzle and directed at

high velocity onto the turbine blades. The entire pressure drop occurs in the nozzles,
converting pressure energy into kinetic energy. The blades change the direction of the
steam flow, which imparts momentum to the blades, causing the rotor to spin.

Examples: De Laval, Curtis, and Rateau turbines.

Reaction Turbines

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 Working Principle: In reaction turbines, steam expands in both the fixed and moving
blades. The pressure drop is distributed across these stages, resulting in both
pressure and velocity changes. The moving blades act like nozzles, and the reaction
force of the steam's acceleration through the blades imparts motion to the rotor.

Examples: Parsons and Modern Steam turbines.

Thermodynamics of Compressible Fluid Flow

Equation of Continuity

The equation of continuity for a compressible fluid is:

d
dx
(ρAV ​ )=0
where:

ρ = fluid density
A = cross-sectional area of the flow
V = flow velocity

Isentropic Flow through Nozzles

Isentropic flow assumes no heat transfer or friction losses, with the relationship:
(γ−1)/γ
T2
T1
​

​
​ = ( PP21 )
​

​
​

where:

T = temperature
P = pressure
γ = ratio of specific heats (Cp/Cv)

Velocity Diagrams
Velocity diagrams illustrate the relationships between the absolute and relative velocities
of steam as it passes through the turbine blades. These diagrams are crucial for
understanding the energy conversion process and for the design of efficient turbines.

Blade Efficiency and Optimum Velocity Ratio

Blade efficiency (ηb ) is defined as the ratio of the work done on the blades to the kinetic
​

energy supplied by the steam:

Work done on blades
ηb = ​

Kinetic energy supplied by steam

​

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 Optimum velocity ratio is the ratio of the blade speed to the steam jet speed for maximum
efficiency.

Multi-Staging
Multi-staging is used to improve the efficiency of steam turbines by dividing the expansion
of steam into multiple stages. This reduces the velocity of the steam at each stage,
minimizing losses and allowing for better control over the energy conversion process.

Types of Multi-Staging

1. Velocity Compounding: Steam passes through multiple sets of moving blades

separated by fixed nozzles, reducing the high initial velocity in steps.

2. Pressure Compounding: Steam expands through multiple pressure stages, with

intermediate pressure drops in each stage, typically used in reaction turbines.

Losses in Turbines
Losses in turbines can be categorized into several types:

Mechanical Losses: Due to friction in bearings and other moving parts.

Thermodynamic Losses: Due to non-ideal gas behavior and irreversibilities.

Leakage Losses: Due to steam leakage past turbine seals.

Carry-Over Losses: Due to water droplets carried over with the steam.

Erosion of Turbine Blades

Erosion is a significant issue caused by solid particles or water droplets in the steam. It
leads to wear and tear of the blades, reducing turbine efficiency and lifespan.

Turbine Governing
Governing is the mechanism of controlling the turbine speed to match the load demand.
Methods include:

Throttle Governing: Regulates steam flow by throttling the steam inlet.

Nozzle Control Governing: Varies the number of nozzles in operation.

Bypass Governing: Directs excess steam away from the turbine stages.

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 Performance Analysis of Turbines
Performance analysis involves evaluating the efficiency, power output, and operational
parameters of turbines. Important metrics include:

Thermal Efficiency

Isentropic Efficiency

Heat Rate

Condensing Systems
Condensing systems are used in power plants to convert exhaust steam from the turbine
into water. This improves the thermal efficiency by reducing the exhaust steam pressure
and allows the reuse of water in the steam cycle.

Components of a Condensing System

1. Condenser: Converts exhaust steam into water.

2. Cooling Tower: Removes heat from the cooling water.

3. Condensate Pump: Pumps condensed water back to the boiler.

Conclusion
Understanding the detailed working, classification, and analysis of steam turbines is
crucial for efficient energy conversion and power generation. Mastery of these concepts is
essential for anyone studying thermodynamics and mechanical engineering.

Anonymous
Suggest me questions with solutions that can come in exam

ChatGPT
Sure, here are some potential exam questions along with their solutions for the topics
covered:

Question 1: Classification of Steam Turbines

Question: Classify steam turbines based on the action of steam on blades and explain the
working principle of each type.

Solution:

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 1. Impulse Turbines:

Working Principle: Steam expands completely in the nozzles, converting its

pressure energy into kinetic energy. The high-velocity steam jet then impinges on
the blades, causing the rotor to spin. The pressure remains constant across the
blades.

Example: De Laval turbine.

2. Reaction Turbines:

Working Principle: Steam expands both in the fixed nozzles (stationary blades)
and the moving blades. The pressure drop occurs over both the stationary and
moving blades, and the moving blades act as nozzles, generating a reaction force
that spins the rotor.

Example: Parsons turbine.

Question 2: Equation of Continuity for Compressible Fluid

Question: Derive the equation of continuity for a compressible fluid and explain its
significance.

Solution:

Equation of Continuity: The mass flow rate of a fluid must remain constant from one
cross-section to another in a steady flow.

d
(ρAV ) = 0
​

dx

where:

ρ = fluid density
A = cross-sectional area of flow
V = flow velocity

Derivation:
Consider a small control volume with inflow and outflow. For steady-state flow:

ṁin = ṁout
​ ​

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 ρ1 A 1 V 1 = ρ2 A 2 V 2
​ ​ ​ ​ ​ ​

Differentiating and simplifying, we get:

d
(ρAV ) = 0
​

dx

Significance: This equation ensures that mass is conserved in the flow of a

compressible fluid.

Question 3: Isentropic Flow through Nozzles

Question: For isentropic flow through a nozzle, derive the relationship between pressure
and temperature.

Solution:
For isentropic processes, the following relationship holds:

(γ−1)/γ
=( )
T2​ P2 ​

​ ​

T1​ P1 ​

where:

T = temperature
P = pressure
γ = ratio of specific heats (Cp/Cv)

Derivation:
Using the isentropic relation for an ideal gas:

P V γ = constant

T V γ−1 = constant

Combining these, we get:

( )/
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 (γ−1)/γ
=( )
T2 P2
​ ​

​ ​

T1 P1
​ ​

This shows the relationship between temperature and pressure in an isentropic process.

Question 4: Blade Efficiency

Question: Define blade efficiency and derive the expression for blade efficiency in an
impulse turbine.

Solution:
Blade Efficiency (ηb ): It is the ratio of the work done on the blades to the kinetic energy
​

supplied by the steam.

For an impulse turbine:

Work done on blades

ηb =
Kinetic energy supplied by steam
​ ​

Derivation:
If Vj is the velocity of steam jet and Vb is the blade velocity:
​ ​

Work done on blades = Vb (Vj cos α − Vb ) ​ ​ ​

1
Kinetic energy supplied by steam = mVj2
2
​ ​

Blade efficiency is given by:

2Vb (Vj cos α − Vb )

ηb =
​ ​ ​

Vj2
​

Question 5: Multi-Staging in Steam Turbines

Question: Explain the concept of multi-staging in steam turbines and differentiate between
velocity compounding and pressure compounding.

Solution:
Multi-Staging: It involves dividing the expansion process of steam into multiple stages,
reducing steam velocity and associated losses, thus improving efficiency.

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 Velocity Compounding:

Steam expands in nozzles to a high velocity.

High-velocity steam passes through multiple rows of moving blades separated by

fixed guide blades, reducing the velocity in steps.

Example: Curtis turbine.

Pressure Compounding:

Steam expands in multiple stages, with intermediate pressure drops.

Each stage includes both stationary and moving blades where partial expansion
occurs.

Example: Rateau turbine.

Question 6: Governing of Steam Turbines

Question: Discuss different methods of turbine governing and their importance in steam
turbine operation.

Solution:
Governing Methods:

1. Throttle Governing:

Regulates steam flow by throttling the steam inlet.

Suitable for small power variations.

2. Nozzle Control Governing:

Varies the number of nozzles in operation to control steam flow.

Used in large turbines for efficient control.

3. Bypass Governing:

Directs excess steam away from the turbine stages.

Used to handle large and sudden load changes.

Importance:

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 Ensures turbine operates at desired speed despite load changes.

Prevents overspeeding and potential damage.

Maintains efficiency and stable power generation.

Question 7: Condensing System in Steam Turbines

Question: Describe the components and working of a condensing system in steam
turbines.

Solution:
Components:

1. Condenser: Converts exhaust steam into water by removing latent heat.

2. Cooling Tower: Removes heat from the cooling water used in the condenser.

3. Condensate Pump: Pumps condensed water back to the boiler for reuse.

Working:

Exhaust steam from the turbine enters the condenser, where it is condensed into
water.

The latent heat from steam is transferred to the cooling water circulating in the
condenser.

The condensate pump returns the condensed water to the boiler feed system,
maintaining the steam cycle efficiency.

These questions and solutions cover key concepts in steam turbine technology and should
help prepare for a detailed understanding of the subject for exams.

Anonymous
Anymore theoretical question?

ChatGPT
Certainly! Here are some more theoretical questions covering different aspects of steam
turbines and their operation:

Question 8: Erosion of Turbine Blades

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 Question: Explain the causes of erosion in turbine blades and suggest methods to
mitigate erosion.

Solution:
Causes of Erosion:

1. Solid Particles: Ingestion of solid particles like dust, sand, or ash in the steam can
cause abrasive wear.

2. Water Droplets: Moisture or water droplets in the steam can cause pitting and erosion
through repeated impact.

3. Chemical Attack: Contaminants in the steam, such as chlorides and sulfates, can lead
to chemical erosion.

Methods to Mitigate Erosion:

1. Filtration: Installing effective filters at steam inlets to remove solid particles.

2. Superheating: Ensuring that the steam is superheated to minimize the presence of

water droplets.

3. Material Selection: Using erosion-resistant materials and coatings for turbine blades.

4. Steam Washing: Regularly washing the turbine to remove deposited contaminants.

5. Steam Quality Control: Maintaining high-quality steam with minimal contaminants

and moisture.

Question 9: Thermodynamic Analysis of Turbine Performance

Question: Describe the thermodynamic analysis involved in evaluating the performance of
a steam turbine.

Solution:
Thermodynamic Analysis:

1. Energy Balance: Applying the first law of thermodynamics (energy conservation) to

the turbine.

Q̇ − Ẇ = ṁ(hin − hout )
​ ​ ​

where:

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 Q̇ = heat transfer rate
​

Ẇ = work done by the turbine

ṁ = mass flow rate
hin and hout = specific enthalpies of steam at inlet and outlet
​ ​

2. Isentropic Efficiency (ηisentropic ): Ratio of actual work output to the isentropic work
​

output.

hin − hout,actual
ηisentropic =
​ ​

hin − hout,isentropic
​ ​

​ ​

3. Heat Rate: Amount of heat input required to produce one unit of work output.

Q̇in
Heat Rate =
​ ​

Ẇout ​

4. Specific Steam Consumption (SSC): Amount of steam required to produce one unit of
work output.

ṁ
SSC = ​

Ẇout ​

Question 10: Governing and Control Systems

Question: Discuss the importance of governing and control systems in steam turbines.
How do they contribute to the efficiency and safety of turbine operation?

Solution:
Importance of Governing and Control Systems:

1. Speed Regulation: Maintain constant turbine speed despite varying load conditions,
ensuring stable power output.

2. Load Matching: Adjust the turbine output to match the demand, optimizing efficiency.

3. Safety: Prevent overspeeding, which can cause mechanical failure and accidents.

4. Efficiency: Optimize steam flow to maintain high efficiency across different operating
conditions.

Governing Mechanisms:

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 1. Throttle Governing: Controls steam admission by adjusting the throttle valve,
effective for minor load variations.

2. Nozzle Control Governing: Varies the number of nozzles in operation, suitable for
larger turbines and significant load changes.

3. Bypass Governing: Directs excess steam away from the turbine to handle sudden
load changes, maintaining system stability.

Question 11: Velocity Diagrams in Impulse Turbines

Question: Explain the significance of velocity diagrams in the analysis of impulse turbines
and illustrate a typical velocity diagram.

Solution:
Significance:

Energy Transfer Analysis: Velocity diagrams help visualize and analyze the energy
transfer between the steam and turbine blades.

Design Optimization: Aid in optimizing blade angles, velocities, and efficiencies.

Performance Evaluation: Provide insights into losses and performance metrics.

Typical Velocity Diagram for an Impulse Turbine:

1. Inlet Velocity (Vj ): Absolute velocity of steam jet from the nozzle.
​

2. Blade Velocity (Vb ): Velocity of the turbine blades.

​

3. Relative Velocity at Inlet (Vr1 ): Relative velocity of steam as it enters the blades.
​

4. Relative Velocity at Exit (Vr2 ): Relative velocity of steam as it exits the blades.
​

5. Absolute Exit Velocity (V2 ): Absolute velocity of steam after leaving the blades.
​

Question 12: Losses in Steam Turbines

Question: Identify and explain the different types of losses in steam turbines.

Solution:
Types of Losses:

1. Mechanical Losses:

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 Bearing Friction: Losses due to friction in bearings and other moving parts.

Windage: Losses due to air resistance on rotating parts.

2. Thermodynamic Losses:

Isentropic Losses: Deviations from ideal isentropic expansion due to

irreversibilities.

Internal Flow Losses: Losses due to friction, turbulence, and shock waves within
the turbine stages.

3. Leakage Losses:

Steam Leakage: Losses due to steam escaping through seals and gland
packings.

4. Carry-Over Losses:

Moisture Losses: Losses due to water droplets carried over with the steam,
causing erosion and inefficiencies.

5. Heat Losses:

Radiation and Convection: Heat losses from the turbine casing to the
surroundings.

Question 13: Isentropic Efficiency

Question: Define isentropic efficiency for a steam turbine and describe its significance in
evaluating turbine performance.

Solution:
Isentropic Efficiency (ηisentropic ): ​

Defined as the ratio of the actual work output of the turbine to the work output if the
process were isentropic (ideal).

Actual Work Output

ηisentropic =
Isentropic Work Output
​ ​

h h
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 hin − hout,actual
ηisentropic =
​ ​

hin − hout,isentropic
​ ​

​ ​

Significance:

Performance Indicator: A measure of how closely the turbine operates to the ideal
process, indicating overall efficiency.

Loss Assessment: Helps identify the extent of irreversibilities and losses in the
turbine.

Optimization: Guides improvements in design and operational strategies to enhance

efficiency.

Question 14: Compounding in Steam Turbines

Question: Explain the concept of compounding in steam turbines and differentiate
between velocity compounding and pressure compounding.

Solution:
Compounding: It is the method of dividing the pressure or velocity drop of steam across
multiple stages to improve turbine efficiency and reduce losses.

Velocity Compounding:

Principle: The steam expands through a set of nozzles, converting pressure energy
into kinetic energy, which is then absorbed by multiple stages of moving blades.

Stages: Includes one set of nozzles followed by multiple rows of moving and fixed
blades.

Example: Curtis turbine.

Pressure Compounding:

Principle: The total pressure drop of the steam is divided among several stages, with
partial expansion occurring in each stage.

Stages: Each stage consists of a set of fixed and moving blades, where the steam
undergoes partial expansion and pressure drop.

Example: Rateau turbine.

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 Question 15: Condensing System in Power Plants
Question: Describe the purpose and components of a condensing system in steam power
plants.

Solution:
Purpose:

Efficiency Improvement: Lowers the exhaust steam pressure to increase the thermal
efficiency of the power plant.

Water Reuse: Condenses the exhaust steam back to water for reuse in the boiler,
conserving water.

Components:

1. Condenser:

Converts exhaust steam into water by transferring heat to the cooling water.

Types: Surface condensers and jet condensers.

2. Cooling Tower:

Removes heat from the cooling water used in the condenser.

Types: Natural draft and mechanical draft cooling towers.

3. Condensate Pump:

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