[Stoves] Water heating fuel efficiency formula

[Ronal W. Larson]

Andrew:  cc list and Lanny

  This is the first time I can recall seeing the number 2.3 MJ/kilo.  This must be associated with some initial moisture?  

   I think Lanny is looking for ways to do testing with wood of different moisture content.  Doesn't he have to do some wood drying in an oven, measuring weight loss?

Ron


On Oct 3, 2013, at 1:07 AM, ajheggie at gmail.com wrote:

> [Default] On Sun, 29 Sep 2013 14:41:32 -0400,"Lanny Henson"
> <lannych at bellsouth.net> wrote:
> 
>> I need the formula or spread sheet, for fuel efficiency, for heating water, 
>> considering the moisture content of wood,  and using red oak as fuel. Not a 
>> water boiling test with simmering,  just a water heating test.
> 
> Lanny 
> 
> What form do you want this to take?
> 
> My guess is red oak will have a calorific content of around the 18.6
> MJ per kilo average suggested for most biomass. When you burn it
> completely it gives off CO2 and water. All the water, both the
> original moisture content and the water formed from oxidising the
> hydrogen atoms in the fuel, in the exhaust contains 2.3MJ of latent
> heat and the sensible heat from the exhaust temperature. This heat in
> water vapour and the sensible heat of the other exhaust gasses, mostly
> nitrogen, any remaining oxygen from the excess air and CO2, is waste
> heat, the other waste heat is the heat conducted, radiated and
> convected from the stove body. The remainder, the usable heat is what
> gets into the pot. 
> 
> The simplest conversion of the potential heat in the wood to usable
> heat in the pot is to weigh the wood used, calculate its heat value
> and measure the rise in temperature of the pot contents and calculate
> the heat input. Divide the first by the second value and you have an
> overall wood to pot efficiency as a first approximation.
> 
> Beyond that you get into the realms of interminable arguments about
> whether to allow for residual energy in any char left and how many
> fairies can dance on a pin head.
> 
> AJH
> 
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