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From: R Andrew Hayden <rahayden@*****.WEEG.UIOWA.EDU>
Subject: TURBINES information
Date: Sat, 30 Jan 93 22:11:14 CET
The Software Toolworks Illustrated Encyclopedia (TM)
(c) 1990 Grolier Electronic Publishing, Inc.



A turbine is a rotary machine that converts the kinetic energy in a
stream of fluid (gas or liquid) into mechanical energy. The stream of
fluid is guided to a rotor, a wheel that is mounted to a shaft from which
power is taken. The fluid strikes a series of buckets, fins, or blades on
the rotor, and the energy in the fluid makes the rotor spin. Turbines are
an example of Newton's third law of motion, which states that for every
action there is an equal and opposite reaction. The earliest known turbine
was built (AD c.75) by the Greek inventor Hero of Alexandria. His device
was a hollow ball that spun in reaction to jets of escaping steam.
Although only a toy, this early reaction turbine demonstrated the
principle later used in the aircraft jet engine.

Turbines may be classed as impulse turbines or reaction turbines,
depending on the force that causes the rotor to revolve. An impulse
turbine is driven by the force of a fluid striking it. In a reaction
turbine, such as Hero's toy, nozzles are mounted on the rotor and revolve
with it.

The three main types of turbines are classified on the basis of the
fluid that supplies the driving force: the gas turbine, the steam turbine,
and the water, or hydraulic, turbine (see WATERWHEEL; HYDROELECTRIC POWER).

Gas Turbine.

The gas turbine is a rotary engine that converts heat energy into
mechanical energy by a continuous process that compresses, heats, and
expands a gas. The basic gas turbine was patented in England in 1791 by
John Barber. In 1930, Frank WHITTLE in England was granted the first of
his many patents for aircraft jet engines, which are essentially gas

A typical gas turbine has an axial or centrifugal air COMPRESSOR that
furnishes a continuous supply of air to a combustion chamber; the
compressor and combustion chamber constitute the gasifier section of the
turbine. In the combustion chamber, fuel is added to the air and then
ignited. When the fuel burns, it produces a hot, high-pressure gas. As the
gas leaves the combustion chamber, it spins the power-turbine rotor (the
power section), which provides power and also drives the air compressor.
The net power available for work from a gas turbine is the power available
from the gases minus the power required to turn the compressor.

Generally, if power is taken mechanically from the shaft of the
power-turbine rotor, the engine is called a gas turbine. In a jet engine,
however, propulsion is provided by a powerful stream of exhaust gas (see

Steam Turbine.

A steam turbine is a rotary machine that converts the heat energy of
steam into mechanical energy. Steam turbines developed little from the
time of Hero to the end of the 19th century, at which time Carl Gustaf de
Laval, a Swede, built several successful single-stage turbines ranging in
size from five to several hundred horsepower. Sir Charles PARSONS in
England and Charles G. Curtis in the United States applied (1884 and 1895,
respectively) for patents on a turbine design in which several bladed
rotors were connected to the same shaft. In this design, the energy of the
steam was put to work in small stages, one after the other. Each stage of
the turbine was larger than the one that preceded it, because the steam
must be expanded to maintain its energy. Using stages, turbines could run
more efficiently at low speeds and could be built in large sizes.

In a typical steam turbine, steam strikes against curved or angular
blades fastened to the movable rotor and causes it to spin. The steam then
meets another set of blades that are fastened to the casing, or stationary
shell, of the turbine; these blades redirect the steam so it can
effectively push against the next set of rotor blades. This process is
repeated as the steam travels the length of the turbine through the
various stages.

Steam turbines provide more than 80 percent of the electricity
generated in the world and power most of the world's largest ships.



Mironer, Alan, Engineering Fluid Mechanics (1979); Sabersky, Rolf H., et
al., Fluid Flow: First Course in Fluid Mechanics, 2d ed. (1971); Shepherd,
Dennis G., Introduction to the Gas Turbine, 2d ed. (1960), and Principles
of Turbomachinery (1956); Staniar, William, ed., Prime Movers, 3d ed.
(1966); Streeter, Victor L., and Wylie, E. Benjamin, Fluid Mechanics, 7th
ed. (1979).



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