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[Anonymous]

Whats the difference between saturated and superheated steam? how was superheating done? Why did some late 1800's and early 1900's locos have extended smokeboxes?

[ndbprr]

Saturated steam is realtively low pressure steam that has water in it that condenses out. Superheated steam is dry and no condensate forms becaus=e of the temperature of the steam. This is important becasue one cubic foot of water makes over 900 cubic feet of steam. Condensate in cylinders has become steam when additional steam was introduced and the resulting transformation has blown cylinder heads of of lcocmotives. That is why you will see engineers of steam engines open a valve on the cylinder to blow out any accumulated water when initially starting. You get a semester all about this stuff called thermodynamics if you take engineering courses in college. A locomotive feedwater heater is a heat exchanger that takes the heat from the waste gasses going up the stack and extracts more heat from them. It is kind of a miniboiler that heats the water before it enters the boiler. It doesn't get the water to boiling it just preheats it so the boiler becomes more efficient. Some roads like the New Haven and Southern mounted the bolier at the top front of the smokebox. It looks like a section of 8-12" pipe running across the top. One of the New England roads used what is called a Coffin feedwater heater that is just plain ugly and looks like a saddlebag on the top and side of the smokebox. The real reason superhearing became practical was the knowledge generated from early engines that resulted in much thicker boilers and better alloys capable of withstanding higher temperatures and pressures. It is just a case of being able to heat the steam to a higher temperture than 212 Degrees. It is heated to temperatures well above 300 degrees and higher. This also allows higher pressures which create more thrust. There is the universal gas law which states the volume x pressure divided by temperature at one condition has to = the volume x pressure divided by the temperature at the new condition. To make it simple if you have a volume of 1 at a pressure of 1 and a temperature of 1 you have 1x1/1 which = 1 no matter what you do to change things it has to = 1 so if you double the temperature to 2 you now have 1x1/2 which = 1/2 and that can't be so either the volume has to double or the pressure has to double so you have 1x2/2 which still = 1