Steam Technology / Basic Steam Theory

If some explanations seem to you to be laboured or too elementary please have patience and remember that there are others who will appreciate and better understand the simplified approach.
If you come across any words or phrases that are unfamiliar to you in the Steam Theory Pages, please email them to me so that I can create a glossary of terms.

What is steam?

We all know what happens when the kitchen kettle begins to boil. Steam comes out of the spout and if the lid isn’t a good fit it begins to bob up and down.
What happened inside the kettle between putting in the cold water and the steam coming out of the spout?
Almost as soon as you put the kettle of cold water on the fire, or the burner, the heat began to make its way through the metal of the kettle and into the water. The continuous flow of heat warmed up the water and made it hotter end hotter until the water began to boil.
As soon as the water began to boil it had reached the stage where it couldn’t take in any more heat. But as the kettle was still on the fire, or the burner, heat was still trying to get into the water. What happened then?
A change took place in the water. The extra heat that was trying to find room in the water was shot out immediately in the form of vapour. In other words, the extra heat began to evaporate or convert the water into vapour.
This “water vapour” is what is known as “steam”.
If we left the kettle alone long enough the water would continue to be evaporated by the incoming heat until all of it had been converted into steam.

Why do we use steam?

Why do we use steam for heating workshops and rooms; for boiling jam; for turning wet stock into paper; for heating the water that washes dirty clothes at laundries or cooking cans of peas; for evaporating chemical liquors; for driving turbines and engines and pumps; for doing the thousands of jobs in all branches of industry? Why steam in particular? Why is it in such common use throughout the civilised world?
It is because there is such a common need for heat and pressure energy (or power energy, if you like) and steam happens to be such a convenient and economical way of conveying large quantities of heat and pressure energy from one place to another. Steam is easy to make and it is made from water of which there is plenty in the world. Steam is easy to control and is such a very versatile commodity.
For a very simple demonstration of the heat and pressure energy in steam, let's go back to the kettle in the kitchen. First, we will test the steam for hotness. If you put a thermometer into the boiling water and again into the steam at the mouth of the spout, the second reading would be the same as the first because the steam is the same temperature as the boiling water.
Now let’s test the steam for pressure energy. This time we don’t need to measure temperature. All we need do is watch the kettle lid bobbing up and down. It is the pressure energy in the steam which is making the lid bob.

See HEAT IN STEAM for the continuing story...


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