You guys ought to be ashamed

[MrWhoopee]

forgive me, I only minored in Physics. Please be kind enough to explain to us all how this heated water vapor goes through the same heat exchange pathway as all of the other combustion gasses but magically does not get conducted into the room ?????opcorn:

To regain the heat required to vaporize the water, the vapor must be recondensed into liquid. If the stack gases were cooled that much, the chimney would cease to draw (or at minimum draw very poorly) and you would need a drain at the bottom. Even with kiln dry wood, attempting to recover too much heat from the stack gases results in a stove that smokes and will not draw.

As to the issue of stacking versus heaping (piling), I make no claims. I merely pointed out that, as nearly as I could tell, neither study addressed that issue. We have several well respected members of this forum who heap their wood. We think no less of them (well, maybe just a little).

Regarding the 20% MC, it is not an absolute number. It is a somewhat arbitrary number considered to be "dry enough". Lower numbers are better, though they can be hard to achieve in areas with high humidity and, according to the calculations, result in only marginally higher heat output. Higher MC wood will definitely burn, but as pointed out in the study YOU referenced, higher MCs result in lower heat recovery. This is true, despite your difficulty grasping the concept. Perhaps your education is interfering with your understanding. To paraphrase a sig line "Your stove will obey the laws of physics, even if you don't understand them."

 

[ajreid]

Plan man, You stated you buy your wood by volume. Buy the dry wood, You will get more wood, no need in buying water.

 

[farmer steve]

as the O/P said.




Now what do I do with all the miss guided knowledge?

Brian[/QUOTE]

 

[Whitespider]

...pissing a guy off who claims to have a pulsating brain, Priceless !!!

Man... your misunderstanding just continues.
You ain't even come close to pissing me off... if you had, I'd have come flat out and told you so.
It's just that I don't argue with simpletons (especially educated simpletons)... they lower me to their level and beat me with experience.

 

[CTYank]

You're missing a lot.
First of all, combustion gasses do very little to heat your stove, those gasses must come in direct contact with the steel in order to conduct some of the heat to it. Heat radiation is what mostly heats the stove steel... for the most part, heat contained in the combustion gasses is lost through the flue because it radiates very little.

Not necessarily so. Where'd you get this info?

My little Morso stove has a baffle that blocks off line-of-sight from firebox to stove-top area (where most of the heat dissipation occurs.) And the secondary combustion of the wood gas occurs (very completely, mind you) right under said baffle. IR will have a hard time through all that metal, but probably contributes a lot to keeping firebox temps high and promoting complete combustion.

Sure seems like the stove-top and the part of the sides just below the top are quite efficient at taking heat from the gases and dissipating it into the room. This means of energy transport features prominently in the gas and oil furnaces I'm familiar with too.

The single-wall run of smokepipe seems pretty efficient at extracting yet more heat from the gases.

So, I would not say it's radiation to the exclusion of conduction. (I'll take all I can get.)

Not a physics major either, just an engineer.

 

[Whitespider]

...I would not say it's radiation to the exclusion of conduction.

Exclusion of conduction?? When and where did I state that??

 

[MrWhoopee]

This statement makes no sense to me:

"High moisture content in firewood results in less effective burning of the wood and in a loss of energy in evaporating the water during burning. A cord of paper birch (Betula papyrifera Marsh.) firewood with 15 percent moisture (dry weight basis) would be expected to use an energy amount equal to 470,000 British thermal units (Btu) during burning to evaporate this moisture. An equivalent cord of paper birch that had a moisture content of 80 percent would be expected to use 2.5 million Btu (Ince 1979). The dry cord will produce more than a 12-percent increase in usable heat."

It completely ignores the first law of conservation of matter and energy. They simply minus out the BTU necessary to evaporate the moisture in the wood without any further accounting. The heat contained in this steam don't just magically vanish, it goes through my stoves heat exchange the same way the rest of the combustion gasses do So in the above I should only loose 12% X 1-(stove thermal efficiency %) in my case about 3% or so, or am I missing something ???

Please note that I did not make this statement. This a direct quote from the study YOU cited to support YOUR position. Why would you question your own evidence?

 

[philoshop]

So if I put 9# of water in my cast iron dutch oven and float a 1# piece of wood in it, then set it on a nice bed of hot coals in my stove, I'll get close to the equivalent heat of a 10# piece of wood?
If that's the case I've been spending way too much time on my wood stacks.

 

[Whitespider]

l-m-a-o !!!

 

[planman]

burning green wood

only one problem guys when wood with no moisture burns it produces CO2 and water !

C6H12O6 + 6 O2 = 6 CO2 + 6 H2O


As long as your stove temp is sufficiently high, burning green wood should not effect the combustion efficiency or the heat transfer efficiency of your stove In fact the water should act as a regulator of combustion and slow down the process thereby allowing a longer burn time and depending on the transfer curve of your stove more overall output. Like I said nothing is destroyed or lost just converted. The EPA just doesn't want long slow fires so they say dont burn green wood. Pop your ash pan door and let more O into the equation and you should be just fine.

 

[MrWhoopee]

only one problem guys when wood with no moisture burns it produces CO2 and water !

C6H12O6 + 6 O2 = 6 CO2 + 6 H2O

True, but that water is a by-product of combustion, which is created in the vapor state. The water in your green wood must be converted into vapor, requiring heat of vaporization. Heat of vaporization is not released until the vapor is converted back to liquid. Wood with 20% MC contains 2 lbs. (1 quart) of water for every 10 lbs. of wood. Recovering the heat of vaporization leaves 1 quart of water in your stove for every 10lbs. of wood burned. Wood with higher MC contains proportionally more water. Is there water running out of your stove? If not, the heat it took to vaporize it must go up the chimney with the vapor.

Twist it any way you want, it takes energy to convert water into vapor. Unless the water is being re-condensed (and staying in your stove), the heat of vaporization must leave with it.

I realize that the facts may not change your opinion, but I can guarantee you that your opinion will not change the facts.

I was only a chemistry major, but for some reason they made me take a lot of physics.

 

[planman]

Green Wood

Ill have to disagree with your statement that the water vapor in my stove will not release usable heat until it condenses. Water can be superheated way above boiling even at atmopshere. If my exhaust temp is 600 degrees the water vapor is also 600 degrees. As it exits the stove Im getting usable heat from this super heated water, presumable at the same thermal coefficient as the other gasses flowing through the stove, possible more as water is a great conductor. My objective is to get the stove hot enough so that I can combust all of the byproducts of pyrolysis, but not so hot as to send a bunch of super heated CO and H2O up my flu along with the associated heat. Burning wood that is too dry creates super hot fire. The EPA loves this, as it ensures all of nasty compounds produced by pryolysis are consumed. Thats why they require all of the new stoves to be tuned to let in more oxygen than necessary and no flu dampers. And they all say "only burn seasoned wood", Im intreseted in the most usable heat, not Mr. Green thumbs objective of no combustion byproducts.

 

[FLHX Storm]

First, dang this thread is entertaining!

Secondly: Since I can't prove I ever went to school I'll lead off like this: Mr Planman, you can have your load of fresh cut green wood with a moisture content of 35 to 50% or more and try to keep warm for the winter. The rest of us will use firewood with 20% or less moisture content and we'll see just who stays the warmest. I suspect you'd likely have to use your natural gas or fuel oil in their respective burners to heat your home.

Personally I would love to see you light a fire with any piece of wood with a moisture content above 35%. Post pictures or your just full of yourself! :msp_smile:

 

[Whitespider]

only one problem guys when wood with no moisture burns it produces CO2 and water !
C6H12O6 + 6 O2 = 6 CO2 + 6 H2O

Such a total lack of understanding... coming from such an educated man... which reinforces my decision to drop-out when I did 40 years ago.

Wood burns in three stages…

The first stage is essentially starting and getting the fire going. When the temperature of wood (not the fire or flame) reaches approximately 212°, water begins to boil out. As long as there is free water in the wood, the energy required to boil and evaporate it cannot be used to raise the wood’s temperature much past 400°. During this time, while free water remains in the wood, massive amounts of gases like CO, CO[SUB]2[/SUB] and acids (smoke) are created… more than what would be during primary combustion. Until all the free water is driven off, primary combustion cannot take place and combustion gases cannot ignite (secondary combustion). These gases represent as much as 60% of the potential heat in wood, and all that potential heat is being lost out the flue pipe. The wetter the wood, the longer it remains at this state, and the more potential heat is lost… yes, I said lost!

The second stage. Primary combustion begins shortly after all free water is driven off and the wood temperature (not the fire or flame) reaches 540° upwards to 900°. During this time CO[SUB]2[/SUB] and acids are still being released as gas, with the addition of some others like methane, methanol and yes H2O vapor. But this isn’t free water being released from the wood, it is water being created through chemical reaction of fire itself… i.e. the creation of this water releases energy (heat), it doesn’t rob energy that can be used to heat the wood. During this stage secondary combustion (ignition of the gases) is possible… but only if conditions are right. The gases cannot ignite at the primary combustion point because all oxygen is being consumed… air must be added to the gases. At the same time, adding too much air (like opening your ash door) will cool the fire and/or gases enough to kill, or at best reduce combustion of those gases (yup, more potential heat lost!). Combustion gas temperature must be maintained at 1100° or better to achieve efficient secondary burn… and that ain’t possible until wood temperature is at its highest during primary burn. That’s why the secondary air is pre-heated and regulated in a stove or fireplace designed to burn those gases… opening your ash door only reduces secondary combustion (or even eliminates it).

The third stage is the coal bed… it don’t apply here.

Synopsis: It matters very little how hot your fire is when you throw wet wood on it, potential heat is lost in large amounts until all free water is driven from the wood… the more water, the more potential heat lost. Opening your ash door in an attempt to keep the wet wood burning by adding more air only causes you to waste more potential heat (especially in a appliance designed for secondary burn). This is basic physics (something you supposedly minored in)… it ain’t EPA propaganda. And believe me, I ain’t an EPA fan by any stretch, most anyone here will tell you I have nothing good to say about the EPA… heck, I’m pulling my EPA firebox out after one season of use because I hated it (by-the-way, I installed a flue damper and tweaked the air inlets).

 

[Whitespider]

I realize that the facts may not change your opinion, but I can guarantee you that your opinion will not change the facts.

I could not have said it better !!!

 

[FLHX Storm]

Synopsis: It matters very little how hot your fire is when you throw wet wood on it, potential heat is lost in large amounts until all free water is driven from the wood… the more water, the more potential heat lost. Opening your ash door in an attempt to keep the wet wood burning by adding more air only causes you to waste more potential heat (especially in a appliance designed for secondary burn). This is basic physics (something you supposedly minored in)… it ain’t EPA propaganda. And believe me, I ain’t an EPA fan by any stretch, most anyone here will tell you I have nothing good to say about the EPA… heck, I’m pulling my EPA firebox out after one season of use because I hated it (by-the-way, I installed a flue damper and tweaked the air inlets).

What? You mean to tell me this isn't Rocket Science? Oh the horror! :msp_scared:

 

[MrWhoopee]

Ill have to disagree with your statement that the water vapor in my stove will not release usable heat until it condenses.

You have misquoted and apparently misunderstood my statement (again). What I said was "Heat of vaporization is not released until the vapor is converted back to liquid."

Here is a refresher on "heat of vaporization"

Enthalpy of vaporization - Wikipedia, the free encyclopedia

This is the energy required to convert liquid water into vapor. It is not released until the vapor returns to liquid.

Despite your attempts to misdirect this discussion, the point is that burning wet wood reduces the amount of heat available to heat your house.
Remember the study you cited in the beginning? http://www.fs.fed.us/pnw/pubs/pnw_rn450.pdf

It states (quite clearly)

"High moisture content in firewood results in less effective burning of the wood and in a loss of energy in evaporating the water during burning. A cord of paper birch (Betula papyrifera Marsh.) firewood with 15 percent moisture (dry weight basis) would be expected to use an energy amount equal to 470,000 British thermal units (Btu) during burning to evaporate this moisture. An equivalent cord of paper birch that had a moisture content of 80 percent would be expected to use 2.5 million Btu (Ince 1979). The dry cord will produce more than a 12-percent increase in usable heat."


So far, you have posted links to four different sources, NONE of which supported your assertions. In fact, the two scientific studies you cited contradicted your claims. An experimental method of burning wet wood chips does not apply to this discussion, neither does the video of a chimney with nothing coming out of it.

Are you sure you went to college?

 

[philoshop]

opcorn:

 

[planman]

wet wood

Actually I was a college professor for 10 years I taught statistics, econometrics, accounting and finance. Here's my last for all you geniuses,

Wood and Bio Mass Heat


As per the above you get a whopping 15% more heat from wood zero moisture which you will never achieve by splitting and stacking. So how much more do you get by volume, which is how I buy my wood, between 20% and 50%. Once again not worth my time.

 

[NSMaple1]

Geebus - there's rocket surgeons all over this place.

What would happen to your stove fire if you open the doors & throw a gallon of water onto it? Same thing as burning a 40 lb load of 40% wood vs. 20% wood.

(Never realized birch was a softwood either....)