PO. Box 308 W. Frisco Blackwell, Oklahoma 74631
It is not enough for the steam engineer to understand how to
start and stop his engine, but he must understand its construction,
have a complete knowledge of his boiler, and the fundamental
principles of steam, heat, and water.
Almost every engineer knows what steam is, but not all of them
can define it. Steam is an elastic fluid resulting from the
combination of heat and water. When steam is in contact with water
from which it was generated, but without water held in suspension,
its temperature corresponds to its pressure and it is known as dry
steam.
If it holds water in suspension, it is called wet steam, but if
subjected to more heat after being separated from the water that it
was generated from, its temperature is then increased without
producing a corresponding increase of pressure, it is then called
super-heated steam. To put it simply, super-heated steam has a
higher temperature than its pressure calls for, and in this
condition it is nearly a perfect gas (called gaseous steam).
When we build a fire under a boiler the water directly above the
fire is heated first and as a natural consequence rises to the
highest point possible (the dome).
The space vacated by this water is filled by water rushing
forward and the space vacated by this water is in turn filled by
the heated water that arose to the surface.
In order that we may make some calculations, we need a standard
unit of measure of heat. This is called the British Thermal Unit
(B.T.U.). This unit means the amount of heat required to raise the
temperature of water one degree. For example: To raise one pound of
water from 32 degrees to 212 degrees requires 180 heat units (212
minus 32), and to raise 75 pounds calls for (75 x 180) 13,500 heat
units. This is because of latent heat. We will assume that the
temperature of the water is 32 degrees because at that point it has
attained its maximum density.
After many heat units have been added to the water in the
boiler, steam is generated, and as more heat is applied, the
pressure increases, the amount being indicated by the steam
gauge.
When water is at 32 degrees Fahrenheit it is at its maximum
density, because the molecules lie as closely together as possible.
If heat is applied until 212 degrees is reached, they continue to
separate, and if more heat is applied they are forced much farther
apart, and the water is turned into steam.
The pressure is light at first, but as more water is evaporated,
the pressure increases, the molecules are forced closer together
and the steam becomes more dense.
Heat is a form of motion, so the greater the temperature the
more rapid will be the motion at the water molecules.
But the real power from steam is its latent heat, or its ability
to store up heat.
For example, if we take a block of ice weighing one pound, and
begin to supply heat it will grow warmer. But at a certain point it
stops growing warmer, even though we keep on adding heat. As we
continue to add heat, the water will grow warmer, but at a much
slower rate. It now takes about double the quantity of heat to
raise the pound of water one degree than it did before; until it
reaches 212 degrees Fahrenheit.
Here we reach a critical point. No matter how much heat we
apply, the water, as water, cannot be heated any more, but changes
into saturated steam. And it is not until we have added enough heat
to have raised the temperature of the water to 1,178 degrees that
it has all become steam, which steam is at the temperature of 212
degrees.
And so four-fifths of the heat which has been added to the water
has disappeared, and cannot be measured by instruments. In short,
the heat which has been absorbed by a pound of steam is sufficient
to have melted three pounds of steel or thirteen pounds of gold!
This is called latent heat; and in it lies the ability of the steam
to do work. For example: at the Oklahoma Steam Show in Pawnee,
Oklahoma, Kenneth Kelley’s 110 Case caused the rubber blocks on
the Prony brake to begin melting! It produced nearly 5,000 ft.-lbs.
of torque! For those who don’t understand how much power that
is, the 1995 Chevrolet Camaro produces 325 ft.-lbs. As far as I am
concerned, steam is the most powerful source of energy.
