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

[George Riegg Gambia]

Hi Steve / Crispin / Roger of Fireside

I'm another of these guys who just hasn't got the tech. language or knowledge so I rely on our experts here and I just try to understand and comprehend.

Looking at Crispin's and Steve's posts about 4 hours apart addressing just about the same topic explaining to Roger the ins and outs of ...... call it energy efficiency / need/ release...... I can understand that Roger is getting confused watching this group.

I see 2 explanations using different methods and by having to make assumptions I accept that the results may vary to a certain degree. But Steve, to say that 5 lb "just about" are 2 kg (it's actually "about" 2.27 which is a 10 % difference which is when multiplied up ALOT).

I really haven't got the time to do alot copy and pasting here but you both use different base figures to calculate the same thing and OF COURSE end up with totally different results:
Crispin 2.68 hrs at 100 % efficiency
Steve 1.6 hrs (efficiency not declared)

Confusing? Of course. And maybe we see now 2 days spent analysing why there is that difference. Maybe THAT's what Roger means when he says lets just get on with doing things. I agree. BUT also let's try to get the science to a level where we see the same results from different people - because if we can't get TAHT right how are we expecting to be taken seriously from either newcomers to the group or the "world at large" when we go out there and lobby for these 1 billion stoves (or, like some of us, actually trying to get them where they belong)?

OK, off the box - gotta get out there to these people here in sunny/rainy Gambia and try to explain to THEM why and how it all works...... wished I could be clearer in MY head!

Cheers
George from the ever depleting jungle!

  ----- Original Message ----- 
  From: Steve Taylor 
  To: Discussion of biomass cooking stoves 
  Sent: Wednesday, July 27, 2011 8:19 AM
  Subject: Re: [Stoves] WorldStove replies to BioFuelWatyche's latestimprecisereporting of facts.


  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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