|MadSci Network: Physics|
Interesting question. And actually, much more difficult than it would first appear! I would like to point out, initially, that I am from Canada and our dollar bill is now a coin. Hence, I couldn't simply go to the lab and check this one out! (Nor was I willing to burn up a five dollar bill for the sake of science.) So, what is the heat content of a dollar bill? At first blush, one might think to simply look up the heat of combustion for paper (13.21 kJ/g - give or take - or 12.44 Btu/gram) and then look up the mass of a dollar bill (3.46 ounces per 100 or 1 gram per bill). Using these two numbers, the answer would then be 12.44 Btu per dollar bill. Except that dollar bills aren't made from paper. Paper money is actually made from "linen" and the rag content of the money is supposed to be a secret to protect the money supply from counterfeiters. That said, it would appear that the paper money is typically about 25% cloth - and since linen is a cellulosic material, it should have pretty close to the same heat of combustion. However, its burning characteristics are significantly different from paper. Also, paper money is printed with inks and such. They will reduce the heat content available from a dollar bill as the inks tend to be inorganic and not particularly combustible. Some of the heat content available from burning the cellulose would need to go into volatilizing the ink. Hence, it would be slightly less than 12.44 BTU per bill. But probably not a lot. To further complicate things, though, if you were to actually burn money to generate electricity, you would have to deal with the issue of combustion of the dollar bills. They don't burn very well when piled together. There is no way for oxygen to get to the core of the stack and hence, they tend to burn on the surface. Try burning a telephone book to see this effect. Consequently, if you truly want to compare the burning of money with say a fuel like methane (natural gas), you need to account for the efficiency of the combustion process. Natural gas burners operate at virtually 100% combustion as it is easy to mix oxygen and gas. Burning money is going to be significantly less efficient - probably closer to 30% - unless the money is either introduced one bill at a time or burnt in an incinerator where there is some other source of fuel for the flame (i.e. natural gas). The "straight up" recoverable energy is probably closer to 4 BTU per bill. And then there are the inefficiencies associated with converting heat to steam and using the steam to drive the turbines and the turbines to driven the generators that produce the electricity. I have seen this number quoted as 23% but I suspect that is a little low. One the other hand, it is not even close to 100%. So, is burning "money" energy efficient? Probably not. At 13,210 joules per gram and with one watt being one joule per second, a paper bill could run (at 100% energy conversion) a 1500 Watt hair dryer for about 9 seconds. Not enough time to really dry your hair. And realistically, if you take all of the inefficiencies and losses due to conversion into account, that time is probably closer to 1 second. On the other hand, with soaring fuel prices, sometimes it does feel like we are burning money! Hope that answers your question.
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