Unit No:02Energy Conversion Devices

Prof. Yash B. ParikhM.Tech (Computer Integrated Manufacturing)

B.E.(Mechanical Engineering)Assistant Professor

Department of Mechanical Engineering

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Preface

When you go to an airport and see the commercial jets there, you can't help but notice the huge engines that power them.

Most commercial jets are powered by turbofan engines, and turbofans are one example of a general class of engines called gas turbine engines.

You may have never heard of gas turbine engines, but they are used in all kinds of un expected places.

For example, they are used in many of the helicopters, smaller power plants and even in the M-1 Tank.

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History

The word "turbine" was coined in 1822 by the French mining engineer Claude Burdin.

It’s derived from the Latin word turbo, which means a spinning object.

During the 18th and 19th centuries, much progress was made toward extracting the kinetic energy of flowing water.

This in turn devised water turbines.

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Introduction

Turbines are devices that spin in the presence of a moving fluid.

A turbine looks like a large wheel with many small radiating blades around its rim.

There are four broad classes of turbine:water (hydraulic), steam, wind, and gas.

The most important application of the first three is the generation of electricity; gas turbines are most often used in aircraft.

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Steam Turbine

Most power plants use coal, natural gas, oil or a nuclear reactor to create steam.

A steam turbine is a rotary machine which is designed to convert the energy of high pressure and high temperature steam into mechanical power.

The steam runs through a huge and very carefully designed multi-stage turbine to spin an output shaft that drives the plant's generator.

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Principle of Operation of Steam Turbine

The high pressure-low velocity steam is first expanded in a passage (called as a nozzle) which converts the steam into low pressure-high velocity jet of steam.

The resultant high velocity steam is passed over the curved vanes (or blades).

Due to this, there is a change in momentum and it will exert a resultant force on the blades.

These blades are attached to a disc on a shaft which is free to rotate.

The resultant force cause the rotor to rotate, and thus the power is developed.

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Types of Steam Turbine

There are mainly two types of steam turbines :

1. Impulse Turbines

2. Reaction Turbines

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Impulse Turbine

These turbines use the principle of impulse. In which the stationary nozzles are used to

exert a force on a ring of moving blades.

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Impulse Turbine

Impulse turbines convert the kinetic energy of a jet of water to mechanical energy.

e.g. Pelton Wheel

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Reaction Turbine

Reaction turbines convert potential energy in to mechanical energy.

Reaction turbines develop torque by reacting to the fluid's pressure or mass.

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Reaction Turbine

These turbine does not use nozzles. Water flow is radial from exterior to interior. Flow changes gradually from radial to axial. The pressure of the fluid changes as it passes

through the turbine rotor blades.

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Reaction Turbine

The overall efficiency of a reaction turbine is slightly higher than the equivalent impulse turbine for the same thermal energy conversion.

e.g. Kaplan Turbine, Francis Turbine.

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Difference between Impulse & Reaction Turbine

In an impulse turbine entire pressure energy is converted in to kinetic energy (as in case of a pelton turbine where the nozzle does this).

In a reaction turbine only a part of the pressure energy is converted to kinetic energy (as in case of Francis and Kaplan turbines.)

Impulse turbine is less efficient compared to reaction turbine.

In impulse turbine we get as high as 30,000 rpm speed of rotor which is very difficult to handle.

In reaction turbine rotor speeds are relatively low.

Impulse turbines occupies less space than reaction turbines.

Impulse turbines are used for small scale applications

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Introduction

A gas turbine is an extension of the same concept as that of steam turbines.

In a gas turbine, a pressurized gas spins the turbine.

In all modern gas turbine engines, the engine produces its own pressurized gas, and it does this by burning something like propane, natural gas, kerosene or jet fuel.

The heat that comes from burning the fuel expands air, and the high-speed rush of this hot air spins the turbine.

Gas turbines are used to produce large quantities of power in a self contained and compact unit.

It has got low weight to power ratio than that of I.C.Engines.

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Introduction

Wind turbines, also known as wind mills, use the wind as their motive force.

A wind turbine looks nothing like a steam turbine or a water turbine because wind is slow moving and very light, but again, the principle is the same.