steamy question

molly

I have had so much good luck at getting answers to my questions here, I just have to ask another. How many BTU are there in 1 cu ft of steam -1psi? Any place online where I can get a look at some charts? Merci beaucoups.

Tony Conner

Cubic Feet...

...is kind of an unusual way to think of quantities of steam. Steam is most often in lbs - completely evaporate one lb of water, and you have one lb of steam.

The total heat in 1 lb of steam, at 1 PSIG is 1151 BTU. If that lb of steam condenses, it gives up 968 BTU. This is because the condensate still has heat in it. At 1 PSIG, one lb of steam will occupy 25.2 cubic feet.

All information like this is contained in the "steam tables". They're published in any number of books, usually 2 or 3 pages in the back. What you have to watch, is that most list pressures in "PSIA", this is "absolute pressure", in which the pressure of the atmosphere is counted. "Gauge pressure" does not count the atmosphere, and most pressure gauges in the real world are in gauge, and it's abbreviated "PSIG". 0 PSIG, is the same as 14.7 PSIA. Spirax Sarco's publication "Hook-Ups" has steam tables in gauge pressure. The old Audels books have gauge pressure and the corresponding absolute pressure listed side by side in the pressure column of the tables. I like that - I really like that, and wonder why nobody else uses it. Most of the Audels books have been out of print for years. Every other book I have uses absolute pressure - which is what you need to use for a lot of engineering calculations, but gauge pressure is what the real world uses.