Paul Wong, age 14, of Butte, Mt., for his question:
HOW DOES A TURBINE WORK?
A turbine is a rotary engine that converts the energy of a moving stream of water, a stream or gas into mechanical energy. The basic element is a turbine is wheel or rotor with paddles, propellers, blades or buckets arranged on its circumference in such a fashion that the moving fluid exerts a tangential force that turns the wheel and imparts energy to it.
The mechanical energy from the wheel is then transferred through a drive shaft to operate a machine, compressor, electric generator or propeller.
Turbines are classified as hydraulic, or water turbines, steam turbines or gas turbines. Today turbines power generators that produce one fourth of the world's electric energy. Windmills are technically wind turbines.
The oldest and simplest form of hydraulic turbine was the waterwheel, which was first used in ancient Greece and was subsequently adopted in most of ancient and medieval Europe for grinding grain. It consisted of a vertical shaft with a set of radial vanes or paddles positioned in a swiftly flowing stream or mill race.
The power output of the early waterwheel was about a half of a horsepower. Then improvements were made. In the first century the lower segment of the paddle wheel was inserted into the stream, thus acting as a so called undershot waterwheel. By the second century water was poured onto the paddles from above and additional energy was gained from the falling water. During the Middle Ages waterwheels were delivering about 50 horsepower.
The simplest form of steam turbine is the so called impulse turbine, in which the turbine jets are fixed in place on the inside of the turbine casing and the blades are set on the rims of revolving wheels mounted on a central shaft.
In the reaction turbine, mechanical energy is obtained to sum degree by the impact of steam upon the blades but primarily it is obtained by the acceleration of the steam as it expands.
The efficiency of turbines is inherently high, because comparatively little of the energy developed by the internal energy drop in the turbine is lost. Losses due to friction and turbulence of steam flow inside the turbine are not actual losses. The energy given off heats the interior of the turbine and this heat is passed along to the steam.
The actual efficiency of a turbine may be as high as 95 percent of the theoretical energy made available by the drop in temperature within the turbine. The overall efficiency of a boiler and turbine system is, however, much smaller because a great deal of energy is lost in the exhaust steam that leaves the turbine.
Although turbines are comparatively simple machines, having only one moving part, the shaft or rotor, a certain amount of auxiliary equipment is necessary for their operation.
Gas turbines work much like steam turbines, but use hot gases instead of steam. Any burning fuel produces hot gases such as those you see in the flame of fire. Gas turbines use these hot gases directly, without first using them to heat water into steam.