Steam Engine - Part 2

The boiler starts each day with about 300 gallons of water. The fire in the firebox heats the water adjacent to it, and the smoke and hot gas from the fire pass through the water in the boiler through 54 pipes called fire tubes. The idea behind the fire tubes is that they increase the surface area where the heat from the fire can transfer to the water in the boiler. The fire tubes empty into a chamber called a smoke box at the other end of the boiler from the fire box, and the smoke exits into the smoke box and goes up and out the smokestack.

The firebox is the hottest part of the boiler. The smokebox end is warm but noticeably less hot, much of the heat having been transferred to the water inside the boiler.

The smokestack provides a column through which the smoke and heated gas from the fire can rise and accelerate unimpeded by the cooler air of the atmosphere, and as it does so it creates a draft that draws fresh air into the fire box and helps the fire to burn hotter.

Depending upon the temperature of the water and the air, it generally takes about 40 minutes to get that much water to a boil. It starts as the sound of an occasional bubble erupting in water and increases in volume and rapidity until it becomes constant in a furious boil. After the boiling starts, and it generally takes another 40 minutes to generate enough steam to run the engine. About 12 pounds of steam engine is enough to start the engine and keep it running without a load, so more pressure would be needed for it to perform work. The noise of the boiler drops off as the pressure increases to the point where it became a barely audible hiss.

Water heated in an open pan on a stove will rise in temperature until it boils at 212 degrees Fahrenheit (or 100 degrees Celsius). More heat applied to the pot will increase the rate at which the water boils, but it will not raise the temperature of the water remaining in the pot. In a closed vessel, like a boiler, the increasing pressure raises the temperature at which water boils -- the boiling continues, but the application of additional heat also raises the temperature of the water above 212 degrees Fahrenheit (or 100 degrees Celsius).

As the water boils, steam is generated, and the steam rises and collects in the steam dome, a hump on top of the boiler. Steam is a clear gas. The cloudy vapor you see coming from the mouth of a steam kettle is a mixture of clear and droplets of water. The steam dome permits the steam to rise above the water and become dry ridding itself of the droplets. The steam that powers the steam engine is taken from the steam dome. Using dry steam improves the efficiency of the engine.

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Photos of the steam engine at Hagley are posted on Facebook:

https://www.facebook.com/gil.hahn.3/media_set?set=a.627985140634731.1073741830.100002697535785&type=3