[Stoves] Testing with wet wood

[Ashok Mathur]

Dear DaleWhen you burn wet wood, you going to use the energy within the wood to make the water evaporate.Say ten percent wet wood will mean that ten percent of weight will be water that will require it be converted into steam. As latent heat of evaporation is huge, fuel efficiency will come down by magnitudes.So don’t use wet wood to burn a fire.Ashok


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On Saturday, July 30, 2022, 2:25 AM, Andreatta, Dale A. <dandreatta at sealimited.com> wrote:

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Stovers,
 
  
 
I believe we should be doing tests with wet wood, and here is a method to make this easier and more repeatable.  The method makes use of two basic ideas. 
 
  
 
First, don’t try to test at a specific moisture level, rather, test at a series of somewhat random moisture levels, then graph the results you want.  For example, suppose you wanted to determine the effect of moisture level on time to boil, covering the range from 10 to 30% moisture, and you have the resources to do 15 tests.  Don’t try to do 5 tests at 10%, 5 tests at 20% and 5 tests at 30%.  Rather, do 15 tests at random levels of moisture covering the range from 10-30, then graph the results.  There will be scatter in the data no matter how you do it, but this method should be much easier. 
 
  
 
The second basic idea is that I think the moisture content of wood is strongly correlated with density, for a specific type of wood.  Thus, do tests with cut lumber whose volume is easily measured, measure the weight, then calculate the moisture content from a correlation that is valid for that type of wood.  Dunk the wood in water to get high moisture content.  The attached graphs show such a correlation for the lumber I used.
 
  
 
This would be rather than doing drying tests, which are accurate but tedious, and this would be rather than using electrical methods, which are sometimes not accurate.  With this method you would do drying tests once for each type of wood, then use that moisture vs. density correlation for all other tests with that type of wood. 
 
  
 
Details of the process:  at the beginning of a testing program you would take some samples of wood.  If you only have a gram scale each sample should be over 100 grams, if you have a more accurate scale it can be smaller.  Each piece of wood should be such that its volume can be measured accurately, with straight sides.  A good caliper is needed, and the wood must be rectangular. 
 
  
 
Weigh the wood, and calculate the density.  Then dry it thoroughly, 8-24 hours in an oven of about 105 C, measure the volume again, and weigh it again.  Again calculate the density, now at a known moisture content of 0.  You can also back calculate the initial moisture content.  
 
  
 
Then throw it in water for a while.  After a while take it out of the water, let it drip and sit for about 24 hours to let the water soak in uniformly, then measure the volume and weight again.  Calculate the density and moisture content in the wet state.
 
  
 
Then graph all the moisture contents vs. densities to get a graph something like the attached graph.  If you haven’t covered the range of moisture content you want yet, throw the wood in the water some more. 
 
  
 
Since this wood will be rectangular, and most natural wood is round(ish) one could make a little fixture to hold the wood at an angle in the stove, corner down, so that the air flowed over the wood in a more natural way.  For stoves like the Jet Flame, with which I’ve been working a lot recently, the correct wood angle could be very important. 
 
  
 
Dale
 
  
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