William McGrath, age 13, of Rockford, I11., for his question:
HOW DOES A STEAM ENGINE WORK?
Energy of expanding steam is what makes a steam engine work. But the engine does not actually create power. It uses steam to change the heat energy released by burning fuel into rotary or back and forth motion that can do work.
Each steam engine has a furnace in which wood, oil, coal or some other fuel is burned to produce heat energy. In atomic power plants, a reactor serves as the furnace and splitting atoms produces the heat.
Each steam engine also has a boiler. The heat from the burning fuel changes water into steam inside the boiler. The steam expands, or takes up many times the space of the original water.
This energy of expansion can be used two ways: to push a piston back and forth or to spin a turbine.
Steam turbine engines produce a rotary motion. Rotary means turning around on an axis, such as a wheel. A steam turbine has many sets of bladed wheels mounted on a long shaft. The steam enters at one end and spins the bladed wheels as it gushes past them.
Steam turbines are used to turn electric generators and ship propellers.
Piston steam engines have pistons that slide back and forth in cylinders. Various systems of valves allow the steam to enter a cylinder and drive a piston first in one direction and then the other before they exhaust the used steam.
These engines are often called reciprocating engines because of the back and forth or reciprocating motion of their pistons. Steam hammers used to drive piles and to forge metal require this kind of motion.
A locomotive requires rotary motion to turn its wheels. This rotary motion is achieved by attaching a crankshaft to the ends of the pistons.
In some types of reciprocating steam engines, called compound engines, the steam may flow through as many as four cylinders and operate ,four pistons.
Steam is water which has been changed into a gas. Steam cannot be seen because it is colorless.
The cloud of vapor you see beginning about an inch from the spout of a teakettle is not steam. The real steam is in the space that seems vacant, just outside the spout. The cloud you see is actually water that the cooler air has changed from gas form back into tiny water particles.
Steam can be formed by boiling or by evaporation. At sea level, water boils when it is heated to the boiling point, or 212 degrees Fahrenheit. The steam caused by boiling.is as hot as the boiling water. The steam caused by evaporation is not hot. Usually the word steam refers to hot steam.
When water reaches the boiling point, bubbles of steam begin to rise through it and escape into the air. The temperature will remain at the boiling point until all the liquid has become gas.