Adios Pantalones said:1)It's by weight. We typically use weight of water/total weight of wood + moisture.
2) you first need to multiply the mass of water in the wood x rise in temp to ignition x heat capacity of water (1 cal/g C).
Then add the product of the # moles water x molar enthalpy of vaporization.
Then add any additional heating of the gas (vapor heat capacity x g x temp change).
Convert to "per pound" and subtract from BTU/pound of wood (which is normally tabulated at something like 20% moisture- so only do the heat calc for the water amount OVER 20% mc in the wood).
fossil said:A pound of water requires 1 BTU to raise its temperature 1 degree F...until it gets to its boiling (or saturation) point, which depends on the pressure it's under. Since we don't run our woodstoves pressurized, we're normally talking in the expected range of atmospheric pressures spanning our elevations...not a great deal of difference so far as water's concerned. Let's just say we're at sea level and normal atmospheric pressure, then the saturation (boiling) temperature is 212 F. We've expended 1 BTU per degree of temperature change to get the pound of water in our wood up to 212 F. Now, in order to turn that pound of water into steam at 212 F, we have to pump in the latent heat of vaporization, which is roughly 1000 BTU's, if I recall correctly, something in that magnitude, anyway. So, we've burned a bunch of wood to heat a bunch of water, then burned a bunch more wood to turn the hot water into steam, and now all that steam is going to go up our stovepipes, carrying all our heat with it, just itchin' to lose its latent heat and condense back into a liquid, depositing all sorts of nasty things with it (what we call creosote). Water...can't live with it, can't live without it. Water in beer = good. Water in firewood = bad. Rick
fossil said:What would you do if you had such an expression? How precise a science do you think this really is? Would you decide whether or not to load another couple of splits before turning in for the night, or you've already gotten enough BTU's in there to see you through? Truly, I think what you're asking for is pretty much impossible to provide, given all the unknowns involved. I think we all burn qualitatively vs. quantitatively, because that's the reality of the process...too many variables to put it in a nice neat closed form equation. Believe me, as an engineer with more than my fair share of OCD, if I could burn by formula, I would. Rick
Obsessive Compulsive Disorder ;-)Apprentice_GM said:What's OCD? Off-the-cuff design?
myzamboni said:JPapiPE said:Jags said:ScottF said:Wow! Just think how smart A.P. would have been if they had not kicked him out of school for drawing cartoons!
Yes that was a very educated answer. Im guessing AP is a chemist or an engineer of some sort by profession?
Naaa- he just stayed in a Holiday Inn Express last night.
Nah, he just got his paint brush stuck to the pallet and decided to become a rocket scientist
Remind me never to get into a war of wits with a Potter :cheese:
Cluttermagnet said:Obsessive Compulsive Disorder ;-)Apprentice_GM said:What's OCD? Off-the-cuff design?
I'm not an expert, but I do understand intuitively that the seasoning process is highly variable. The rate of wood moisture loss is tied to many external factors including RH (relative humidity) over time, amount of sun and wind exposure, amount of heating from all sources, mainly the sun if outside, wood type, etc.
I couldn't agree more, I'd also love to have a good, strong rule of thumb which was even a fairly rough estimator. But I think there are just too many variables in the process. The only thing we know for sure is that most all process rates are dependent on differences, i.e. if the wood moisture is quite high, it outgasses at a much higher rate, right after splitting, than we will see at 1 week, and in turn, still less at 1 month than at 1 week, etc. We should probably expect that it is a steeply falling curve at the beginning, and it begins to level out fairly soon. When that curve becomes dead flat, the wood moisture would be in equilibrium with the RH. The absolute difference between the wood moisture and the RH is constantly decreasing, and it is the magnitude of that difference that drives the rate of change.
But RH goes up and down kind of randomly as the weather changes. And our wood gets rained on and 'backslides' a little. We get more or less sun and the rate of outgassing bounces around. Just ask the guys in the US Northeast this year- it rained endlessly up there. Probably a 'bad' year for wood seasoning. I'd think a rule of thumb would only be possible 'per species' (one formula per tree type), and probably only in a predictable, kiln-like environment for months on end.
Apprentice_GM said:...Rick, what I am hoping it could do is a provide a rule of thumb like:
"Mate, I've measured your wood with my moisture meter and it's 30% MC. You'll need to burn 8 cords to get thru this winter . . . or if you leave it season for a year, it'll drop to 20%, and you'll need half that (or 5 cords or whatever). If you can leave it 2 years it'll drop to 10% and you'll only need to burn 3 cords . . ."
Adios Pantalones said:manoman- I go camping and look what happens. Burned lots of high moisture content (read "scavenged") wood this weekend. Kept warm by a good fire despite my tequila consumption.
Adios Pantalones said:manoman- I go camping and look what happens. Burned lots of high moisture content (read "scavenged") wood this weekend. Kept warm by a good fire despite my tequila consumption.
Apprentice_GM said:[
I really would like to know the amount of usable heat lost to moisture content as a % of rated BTU's (measured at 20% MC) over 20% per percentage. Even rough. Rule of Thumb. Ball park.
JPapiPE said:You guys are crazy...most seasoned cord wood for a year is only in the 30% range, and 30-35% is acceptable in Maine for seasoned wood. Board lumber at lumber yards, which is kiln dryed measues about 15%M.C. this time of year. While Master Cabinet Makers will settle for 10-12% ...And Master Furniture Makers will usually have their own stash air drying for 2 years or more. At any rate furniture wood will be about 6-8% ...which is ideal. If you guys are worrying about 30-35% M.C. in your wood pile...DON'T ! you are right on target. I am a Master Joiner/ Finish Stair Builder and have dealt with these values for many years. So don't sweat the small stuff.
Todd said:JPapiPE said:You guys are crazy...most seasoned cord wood for a year is only in the 30% range, and 30-35% is acceptable in Maine for seasoned wood. Board lumber at lumber yards, which is kiln dryed measues about 15%M.C. this time of year. While Master Cabinet Makers will settle for 10-12% ...And Master Furniture Makers will usually have their own stash air drying for 2 years or more. At any rate furniture wood will be about 6-8% ...which is ideal. If you guys are worrying about 30-35% M.C. in your wood pile...DON'T ! you are right on target. I am a Master Joiner/ Finish Stair Builder and have dealt with these values for many years. So don't sweat the small stuff.
30-35% is too wet. 15-25% is what you want to shoot for. Most firewood will reach this after 1 year sitting out in the sun and wind. Anything over 30% will sizzle in your stove, waste BTU's, and most importantly could cause creosote build up and chimney fires.
JPapiPE said:Todd said:JPapiPE said:You guys are crazy...most seasoned cord wood for a year is only in the 30% range, and 30-35% is acceptable in Maine for seasoned wood. Board lumber at lumber yards, which is kiln dryed measues about 15%M.C. this time of year. While Master Cabinet Makers will settle for 10-12% ...And Master Furniture Makers will usually have their own stash air drying for 2 years or more. At any rate furniture wood will be about 6-8% ...which is ideal. If you guys are worrying about 30-35% M.C. in your wood pile...DON'T ! you are right on target. I am a Master Joiner/ Finish Stair Builder and have dealt with these values for many years. So don't sweat the small stuff.
30-35% is too wet. 15-25% is what you want to shoot for. Most firewood will reach this after 1 year sitting out in the sun and wind. Anything over 30% will sizzle in your stove, waste BTU's, and most importantly could cause creosote build up and chimney fires.
If you wait around for 15% You might not be burning wood for the next 2 years...A luxury most of us can't afford!
Todd said:Try a search for firewood BTU’s and you will come up with many different tables. There are lots out there and they usually go by million BTU per cord at a certain m/c. Look for the fine print that will tell you the moisture content for the given numbers. If you can find a few different tables compare the BTU’s and moisture content and maybe you can figure something out.
I looked at two different tables for Red Oak. One table was 20% mc, it had 24 million btu's per cord and the other was 12% mc and had 27 million btu's per cord. So if some math wiz out there can figure out the difference you may get a rough idea on loss or gain of BTU's by moisture content.
Apprentice_GM said:...Beauty! I'm off to find some tables . . .
JPapiPE said:Some of us started later than others in our decision to burn wood...or were forced into it by super- high price increases in heating fuel. We are what we are and we will burn what we have. There is no competition here. We burn what we have... Maybe next year we will be a little ahead of the game, but right now we are stuck... Any wood is better than a gallon of heating fuel... So we don't need be told how bad off we are... We'll make do.
We always do, one way or another...so relax all you excited wood burners with less than perfect wood...we all will make it. Let's let someone else panic, but not us...we are a brotherhood of wood burners and we will survive...by hook or by crook...i did spend all my emergency money on the stove/wood setup...so I am broke just like a lot of you. Don't fret we will persevere and come out on top. Warm and happy
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