[Stoves] WorldStove replies to BioFuelWatyche's latestimprecisereporting of facts.

[Steve Taylor]

Roger.

Here's the maths as I see it.

There is an accepted amount of energy you can extract from a piece of wood.
The very best case  is a piece of oven dried wood, burning in pure oxygen -
which is unrealistic, so from this site
http://www.woodgas.com/fuel_densities.htm I can get a value which I am going
to call 15 MegaJoules per kilogram. A joule is the SI unit of energy. 4.2
Joules heats one gram of water one degree centigrade. We use SI units in
here, because it makes the math easier for everyone.

The group will argue with my choice of 15MJ, but we accept it isn't 10 x
smaller or larger than the "right" value.

A 5 lb log is, near as damn it for the purposes of illustration, 2kg in SI.
That means it contains 2 x 15,000,000 Joules of releasable energy, 30
MegaJoules (MJ)

Now, a rate of releasing energy, in Joules/second is called  a Watt. 1
Joule/second = 1 Watt.

5kW = 5000 J/Sec
To release 5kW, we have to release 5000 joules per second.

You have 30,000,000 Joules in your log. Burning at 5000 J/s, it can do that
for 30,000,000/5000 seconds. That's 6000 seconds, or 6000/3600 = 1.6 hours.

So all things begin equal, and Ron says you are claiming a burn-time of 12
hours, you are releasing energy at 30,000,000 / 3600 / 12....or 700 W

Steve
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