Tredgold's Measure of the Effect of a Fuel

sguthery

One of the books I'm reading these days is Thomas Tredgold’s Principles of Warming and Ventilating. The unit of work that he adopts is what he calls the effect of fuel:

"I take, as the measure of the effect of a fuel, the quantity, in pounds avoirdupois, which will raise the temperature of a cubic foot of water one degree of Fahrenheit's thermometer."

He reports on various experiments for determining the effect of heat for various fuels: e.g.

"From the trials of Mr. Watt, it appears that a bushel of Newcastle coals will convert from 8 to 12 cubic feet of water into steam, from the mean temperature [ed. Tredgold's mean temperature is 52 degrees] of the atmosphere ; and a bushel of Swansea coal will produce an equal effect. The mean weight of a bushel of coals being 84 lbs. and, taking 10 cubic feet as the mean effect of a bushel, it will be found equivalent to heating one cubic foot of water one degree, with 0 0075 lbs. of coal."

A BTU as is well-known is:

"It is the amount of work needed to raise the temperature of one pound of water by one degree Fahrenheit."

A cubic foot of water weighs about 8.3 pounds so this would seem to say that Newcastle coal contains 0.0075/8.3 = 0.0001 BTUs per pound. But all the tables I've found rate Newcastle/bituminous coal at around 13,000 BTUs per pound.

I'm off by about eight order of magnitude here. Where did I go wrong?

Many thanks for any insight.

Jamie Hall

Two problems which I can see off the top of my head -- first, a cubic foot of water is 62.5 pounds, not 8.3 (that's pounds per gallon). Much more important, though, is that there is something amiss in the quote from Tredgold -- but hard to say what. In the beginning of the quoted paragraph, the reference is to converting water into steam; in the last phrase somehow that got changed to raising the water temperature by 1 degree. Just running the numbers in my head I get a figure of about 8,000 BTU per pound of coal --not far off the referenced figure.

Steamhead

Good eye. Basically, the amount of water involved in the definition of a BTU was changed over the years. I'm pretty sure this is covered in the first chapter or two of Lost Art, but don't have a copy with me at the moment.

Gordy

Weight of 1 gallon of water at 62 degrees is 8.34 lbs.

1 cubic foot of water at 62 degrees weighs 62.39 lbs.

1 btu is the energy it takes to raise 1 pound of water 1 degree Fahrenheit.

To raise 1 cubic foot of water 1 degree F. Equals 62.39 btus.
To raise 1 gallon of water 1 degree F. Equals 8.34 btus.
To raise

Mike_Sheppard

@Steamhead you are right. A BTU used to be the amount of heat to raise a cubic foot of water 1 degree, rather than a pound of water one degree. Although it wasn’t called a BTU until after Tredgold was gone.

It is indeed covered in the first chapter of Lost Art, and Dan talks about and quotes from Tredgold’s book.

Leonard

in pounds avoirdupois ..... dead give away that it's an OLD book.

Book sounds like something I had to read in engineering school for the humanities requirement. In school I had to do a paper on the effect of coal on England's Industrial revolution, mostly transport of coal in horse drawn barges by the water canal system. I hated the poor quality and wording of "technical" books back in the day when they were just starting to discover the rules of thermodynamics.

Old book might contain something interesting, but you may have to work to dig it out. I'ld tend to throw the book away and read a modern thermodynamics or heating book. Modern books aren't written with gobbledygook gook , poorly defined terms, and in cryptic old English.

Steamhead

Leonard said:

in pounds avoirdupois ..... dead give away that it's an OLD book.

I school I had to do a paper on the effect of coal on England's Industrial revolution, mostly transport of coal by the water canel system. I hated the poor quality and wording of "technical" people back in the day when they were just starting to discover the rules of thermodynamics.

I'ld throw the book away and read a modern thermodynamics or heating book. Modern books aren't written with gobbaldy gook , poorly defined terms, and in cryptic old English

Au contraire,, if you don't read the old books, you don't know where we've been. That's as important as where we are now.

Mark Eatherton

And here I thought it was two guys in a bar drinking a pint of beer that determined what a BTU was. 1 pint = 1 pound. Raising the temperature of one pint one degree = 1 BTU, no? It got its start as a drinking game in a pub outside of Blarney :-) (altered facts, not fake news...)

ME