How Steam is Developed

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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.