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Hydrogen as a fuel

by chound
Tags: fuel, hydrogen
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Nov26-04, 08:25 AM
P: 239
Is it possible to create a structure where
1)water is electrolysed into oxygen and hydrogen
2)Hydrogen is burnt in the same oxygen obtained from step 1
3)This releases lot of energy and forms water
4)This energy can be used to rotate the armature of an electric generator
5)Electricity can be produced
6)The water in step 3 can be used in step 1
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Nov26-04, 01:06 PM
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Yup, yup, yup, yup, yup, and yup. Will "5" take care of "1"? Nope.
Nov26-04, 02:08 PM
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Since the reaction is symmetrical (water+energy=hydrogen+oxygen=water+energy, etc, etc, etc.), even if you had perfect efficiency, you'd still never get more energy out than you put in.

Nov26-04, 05:15 PM
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Hydrogen as a fuel

Let's do the math here and see what falls out. Per Faradays constant of electrolysis, it takes about 96,500 coulombs to generate 1 mole of hydrogen gas. After a couple of crunches, it appears to require about 32.9 kilowatts to generate 1 kilogram of hydogen gas. The electrical energy equivalent of a kilogram of hydrogen gas is 33.5 kilowatts. That looks promising, 102% efficiency!

Aye, but there is a rub, as usual. Those are idealized numbers - i.e., they assume 100% efficiency. You can take 17% straight off the top in heat loss. Now the numbers look like this 32.9 x 1.17 and 33.5 x 0.83 = 38.5 kw to get 29.1 kw.. down to 75% efficiency. And this is at laboratory efficiencies. In the real world, the true loss is about 1/3, so the real world efficiency is in the neighborhood of 50%. The bad news is you will run out of gas. The good news is it ain't all that bad a return.

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