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Does wood season quicker in winter, since it’s dry? Weird...

Post in 'The Wood Shed' started by thinkxingu, Jan 1, 2010.

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  1. LLigetfa

    LLigetfa Minister of Fire

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    German Shepherd Dog

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  2. Battenkiller

    Battenkiller Minister of Fire

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    LMAO!

    I've seen bumper stickers that say, "Honk if you passed P-Chem". I never honk. But I do know that my sweaty shirt dries lots faster on hot dry days than on hot muggy days. What's the hurry for all that moisture to evaporate? Doesn't it know that relative humidity is irrelevant?

    Enthalpy, schmenthalpy... wood dries in the winter because it's dry outside.
  3. LLigetfa

    LLigetfa Minister of Fire

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    I wonder if living in the Rainy River District has something to do with how my wood dries in Summer? I do know that our wild temp swings in Winter here sure dries out the air.
  4. Battenkiller

    Battenkiller Minister of Fire

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    I figured out the GSD, but not the HM wife. My wife says its the same as her's... "Her Majesty". That true?
  5. Bigg_Redd

    Bigg_Redd Minister of Fire

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    WTF is "P-Chem"?

    I thought Chem stopped at "O"
  6. Adios Pantalones

    Adios Pantalones Minister of Fire

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    A- chem, O-chem, IO-chem, P-chem, biochem...

    A is analytical (also called anal chem), O is organic, IO is inorganic, p-chem is physical chemistry.

    I'm not gonna get into this one anymore- there's a lot of guessing, etc. The plural of anecdote is not data :)

    -pH- passed a few chemistrational classes, and took a class from Bruce Hoadley his own self. OK- Bruce taught me to tie fishing flies, but still...
  7. Arlo

    Arlo New Member

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    Location Location Location... :)

    Here in Eastern PA its humid in the summer. At the start of the winter, half of my wood was seasoned. The other half not so seasoned. Green in fact were many pieces of re-split splits. Since November, my wood has been exposed directly to days on end of 20+mph winds. That same wood is now seasoned. I'm no scientist but I do know this, the freezing cold wind dryed my wood, possibly faster than the humid summer windless days. Like many other people have said here; "its all about location" but wood definetley dries in the winter!!!
  8. LLigetfa

    LLigetfa Minister of Fire

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    It almost could be but it's not. It's High Maintenance.
  9. Battenkiller

    Battenkiller Minister of Fire

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    Well, my brain stopped at O-chem, but the subject itself goes on. P-chem deals with the physics of bonds and reactions and rates and thermodynamics all that stuff you just dipped into in General Chem. Pretty heavy stuff. I struggled with Gen Chem, breezed through O-Chem and hit a wall with P-Chem. Has to do with the way your brain is structured I think. Mine isn't very well structured at all. Dropped out of chem and got a bio degree. Way, way easier.

    Anyway, I won't be bullied by the physical chemistry experts into thinking my wood won't dry well in the winter, at least here in the great Northeast.

    The heat of vaporization has very little to do with the phenomenon. All water has plenty of heat from a physical chemistry point of view (until you start approaching absolute zero), even when it is frozen. At any temperature we are likely to encounter, from -40ºF/C to 125º in the Mohave, the amount of heat in the water is vastly more than at 0º Kelvin (-460ºF, -273ºC). Yes, the heat of vaporization goes down in a relatively linear fashion (determined by many decades of experimental data) as temperature rises, but it is still a hell of a lot at any normally encountered temps. Even at (low) internal stove temps, evaporating water robs you of massive amounts of BTUs until you get up to about 600ºF. That's why you need to burn wet wood hot as hell. At smoldering temps, most of the heat gained from combustion is used up just converting liquid water into water vapor, which further lowers stove temps which robs more heat, etc. It's actually even more complicated than that, but I digress...

    Water molecules enter into the air one at a time. They can only break the strong hydrogen bonds that hold them together when they are at the very surface, or when they are converted to steam bubbles while boiling. Yes, the hotter you get the water, the faster it will evaporate. That's because some individual water molecules at higher temperatures are more energetically favored to overcome the heat of vaporization (which is an experimentally derived figure that is an average for the entire given mass at any given temp) than are others. Does the air in your kitchen need to be hot to evaporate a pan of water simmering away on the back of the stove? Or more to the point, does a hot kitchen allow the water to evaporate a lot faster than a cold kitchen? No, of course not, because the energy comes from the hot water itself, not the air. Temperature and heat are not the same, and anyone throwing physical chemistry terms around should be well aware of that. No matter how high you get the air temperature, there will always be orders of magnitude of difference between the energy contained in the two substances, with water winning the battle by a long shot... even when it is frozen. Temperature is just a measure of molecular motion, not the amount of heat contained. As my prof used to tell us, there is immensely more energy in a bathtub of cold water than there is in a burning match. Case closed.

    Even when winter camping, water will boil away, and at high altitudes and extreme cold it still boils and evaporates (although now at a much lower temperature). Air temps have nothing to do with it, it's the temperature of the water itself that dictates how water turns to vapor at any given atmospheric pressure. Outside your stove (where most of us like to dry our wood), differences in the heat of vaporization at varying temps have very little to do with the drying process. Access to the water inside the wood (by any method) to the air that surrounds it, and differences in relative humidity are what is driving the whole thing.

    Sublimation has very little to do with the process, either. Because the relative humidity is ofter lower in the winter than in the summer in many regions, wood can dry much faster. But if it is solid, it will have to be removed by the process of sublimation. This, as well, has very little to do with the differences in heat of vaporization. It is a slow process because the water molecules don't circulate around when locked into a frozen position, and because... well, there's lots less heat in frozen water. All of the molecules that enter the vapor state must come from the very surface, the only place where they have access to the air. But freeze/thaw cycles expand wood cells and damage them, freeing up some of the water bound inside the cell and liberating it when the wood thaws out. In the living tree, there are numerous mechanisms to stop this, or to repair the damage when it occurs, but once cut, the wood is at the mercy of the elements, which break down the fiber structure. It has to get cold enough to really freeze the wood all the way through. Wood is a pretty good insulator, so overnight temps in the teens just won't cut it, but let the temps drop well below 0ºF for a few days running, and you will get the effect that the old timers I knew used to call "freeze drying". It has nothing to do with partial pressures or vacuums, and little to do with sublimation. It is mostly due to structural damage to the wood followed by low relative humidity of the winter air. LLigetfa hit the nail on the head... wildly changing outdoor temps and conditions are what drive winter drying. But inside a kiln, where the water in the wood itself contains more heat and, therefore, can overcome the heat of vaporization easier, the process certainly does go much quicker than it does at ambient temps.


    Of course... I could be way off here.


    BTW, does everybody know that wood left at a constant RH of 90% will eventually reach an equilibrium MC of about 20% at room temperature? Just takes a lot longer.
  10. iceman

    iceman Minister of Fire

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    my head is spinning..... wow!.... so in conclusion are you saying that wood will dry just as much in the winter as summer as long as the temp doesnt stay below 0??
  11. Battenkiller

    Battenkiller Minister of Fire

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    You're head is spinning? I just got through writing all that. :lol:

    Not exactly. But if you live in a climate like I do, you will get tons of drying done after several freeze/thaw cycles destroy the wood a bit. Temps need to get above 0ºC (but above 32ºF) for the ice to melt again. Liquid water moving to the surface of the wood can evaporate faster than the ice trapped inside the wood can evaporate by sublimation. If the water in the wood stays frozen, is can't very easily move to the outside where it can contact the low humidity air. All water that leaves the wood must do it at the molecular level at the air/water interface.

    A good comparison is freezer burn in your home freezer. Meat or veggies that aren't vacuum packed get pretty dried up in the low humidity of the freezer environment, but the effect is primarily limited to the outside. Of course, as the process continues, it leaves air spaces at the surface that can then contact the water further inside. Eventually, you might end up with a very dehydrated product, but it will take a very long time.

    Best bet is to let it go all winter into the next season. Buy or cut your wood now in the winter and go fishing in the summer like you're supposed to. Let it get good and cracked from the freezing temps and it will dry out even better in the summer. The wood will thank you for damaging it like this, and it will reward you for your cruelty next burn season.
  12. gerry100

    gerry100 Minister of Fire

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    Can't we get along and invoke one of those pesky laws of Thermodynamics?

    If the air is drier than the wood - the wood will lose moisture no matter what time of the year it is.

    If the reverse is true the wood will absorb.

    The structure of the wood means that is reacts to the difference much slower than the air changes.

    Therefore it eventually reaches the average moisture content of the air.

    Eventually usually means 1-2 years, depending on th ewood type,shape etc.
  13. gerry100

    gerry100 Minister of Fire

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    Can't we get along and invoke one of those pesky laws of Thermodynamics?

    If the air is drier than the wood - the wood will lose moisture no matter what time of the year it is.

    If the reverse is true the wood will absorb.

    The structure of the wood means that is reacts to the difference much slower than the air changes.

    Therefore it eventually reaches the average moisture content of the air.

    Eventually usually means 1-2 years, depending on the wood type,shape etc.
  14. ansehnlich1

    ansehnlich1 Minister of Fire

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    ok, ok, ok,

    I admit it...

    I PUT my wood in the freezer to season it :bug:

    Naw, look, my stacks sit at the edge of a walnut grove, they get sun for a half day or more, and prevailing winds all the time. It takes 1, 2, or 3 years to season depending on species.

    And YES, I think it seasons in winter as well as summer.
  15. bogydave

    bogydave Minister of Fire

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    With all the knowledge I just gained from seasoning wood in the Winter I've decided to only season wood in the Winter.
    I haven't figured how to stop it from seasoning in the Spring, Summer & Fall but am working on it. :)
  16. Battenkiller

    Battenkiller Minister of Fire

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    Nope. Doesn't do that either. Like I said, wood dried at 90% relative humidity will eventually reach a moisture content of about 20%, and it will stay that way forever as long as the RH doesn't change. Even if you raise the RH of the surrounding air up to 100%, it won't regain much of the water it lost during seasoning. Counterintuitive... but true.
  17. Rockey

    Rockey Minister of Fire

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    There are many charts that prove this true: http://www.csgnetwork.com/emctablecalc.html

    Your earlier write up was very impressive. I have a suggestion. There are guys whose livings are dpendant upon this very subject. There quite a few sawmills that cut dimensional lumber and air dry it year round. These guys are much more practical experts on the subject than we will ever be. I think a few phone calls can give us a definitive answer. Once again I stand by my original statemnt that "by and large much more seasoning is done during the summer" If I;m wrong I;ll change my username to SisterBart or BrotherFart, take your pick, for 1 week. :)
  18. awfireman

    awfireman New Member

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    You need to use the conversion ruler to determine moisture content when its below freezing. I am in the Forestry Field and any Delhurst Moisture Reader comes the with this ruler. Oak, giving a 20% moisture reading when its 32 or below is really around 28-32% moisture depending how much you get below the freezing mark.

    Fireman
  19. woodgeek

    woodgeek Minister of Fire

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    Ok, watch out, more P-chem and partial pressure...

    If I'm a water molecule in a liquid (or ice) I can hop off into the air. While it does take a little energy for me to do that (since we are below 212°F), there is plenty of energy around--my average thermal velocity is 1000 mph. Batten has a sensible argument. If I'm a molecule I don't care if there are other water molecules out there when I decide to leave the liquid/ice, I only care about my energy change.

    BUT the flaw in the argument is that the opposite can happen. Water molecules in the vapor can decide to rejoin the liquid/ice, and the rate of that happening is directly proportional to the ambient RH. So, 100% RH doesn't prevent H2O molecules from leaving the liquid, it just causes the return process to balance the leaving process, for zero net drying rate.

    The partial pressure concept is the easiest way to describe this. If we put water/ice in a vacuum, it would vaporize until the total pressure of vapor suffices to return vapor to the liquid at the same rate it was leaving--equilibrium. At 212°F, that vapor pressure is 1 ATM, which is why it forms bubbles in water at that temp on the Earth's surface. At lower temps, including below 32°F, the pressure is lower, but not zero.

    After a little googling:
    T (°F) mmHg
    -40 ~0
    12 2
    32 5
    52 10
    72 15
    84 30

    So, this confirms that the drying rate (at 0%RH) 32°F is 1/3rd that at 72°F, or 1/6th that at 84°F. Sounds like a lot, but is tempered by the typical lower winter RH, getting us back to the mild winter (nom 32°F) drying rate being 2-3X less than summer, but not zero. If your typical temps in the winter are <<32°F, then yeah, your winter drying rate is the pits.

    Woodworkers do know, but everything I've read about air-drying dimensional lumber is completely in line with this 2-3X rate figure.
    That is: http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr121.pdf
    which tabulates drying time for different species and locations. Enjoy.

    Yeah--winter drying is just ok by me.
  20. Battenkiller

    Battenkiller Minister of Fire

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    Woodgeek, what you are describing with partial pressures at varying temperature is just the formal way of explaining what relative humidity is all about. Air doesn't "hold" moisture, it's just another gas in the mix. So all we need to know is that relative humidity is temperature dependent. What you are saying is the same thing I'm saying, just using terms that are hard for most folks to grasp.

    There is no flaw in my argument. I never said that water molecules don't go back into the source water, just that they do so at a slower rate than they leave until equilibrium is reached. Equilibrium is temperature dependent for sure, but it isn't only reached at 100% RH, it is reached at any RH between 0% and 100%, at temps between -40ºC and 100ºC (at 760mmHg).

    Even though evaporation rate is directly proportional to changes in partial pressure/relative humidity, it really doesn't matter. Wood is a very complex structure, not a drop of liquid in an enclosed flask. The water is locked inside the structure of the wood fibers, and it's removal rate is dependent on many other things besides just the ideal gas laws.

    And for the record, I never said that wood won't dry faster as temperatures rise, just that it dries a hell of a lot due to the effects of cold weather as well. The fact that I speed dry my wet wood in my stove room (and that it actually works) is enough proof for me.

    BTW, you can't really use data from air-drying dimensional lumber to explain how firewood dries. Dimensional lumber dries mostly through the sides because its exposed surface area is almost entirely along the sides. Firewood dries mostly through the ends because it is short relative to its cross sectional area. Makes a big difference how stuff is cut.

    Regardless, thanks for providing the link to the drying tables. Good information to have no matter where or when you dry your wood. ;-)
  21. IanDad

    IanDad Member

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    P Chem. Yikes! I ran away from it as fast as I could also. This thread is why I love the internet, though.

    Outstanding discussion, and it certainly heartens me after a several days of 30 - 40 mph gusts and temps in the twenties with some stacks of somewhat questionably dry wood.

    Very informative. Thanks to all.
  22. Rockey

    Rockey Minister of Fire

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    Thank you Woodgeek. The proof is within: http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr121.pdf

    Here is a direct quote from the US Department of Agriculture Forest Services -

    "In addition to the effect of summer–winter temperature differences,
    estimates of air drying time are affected by the time of year
    when the lumber is stacked. Lumber stacked in the spring
    may dry in a relatively short time because a large portion of
    the drying may be in the warm spring and summer months. In
    contrast, lumber stacked in late summer or early fall may take
    a relatively long time to dry because it will be exposed to
    winter temperatures, when drying may almost stop."

    The data extrapolated from that research data graphs proves that by far in every region that they tested and for every species summer drying is FAR more effective.
  23. Adios Pantalones

    Adios Pantalones Minister of Fire

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    You sort of are way off on some points :) . If the water is frozen then it must sublime- so I dunno why you say "Sublimation has very little to do with the process, either. ".

    "This, as well, has very little to do with the differences in heat of vaporization. " The standard enthalpy of sublimation for a material is equivalent to the sum of its enthalpy of fusion and enthalpy of vaporization, whereas liquid water only needs to overcome vaporization.

    "you will get the effect that the old timers I knew used to call "freeze drying". It has nothing to do with partial pressures or vacuums, and little to do with sublimation."

    Water going from a solid to a vapor is sublimation. I don't care if it's solid wood, lignum vitae, damaged balsa, or mashed potatoes. If it's frozen, then drying is by sublimation. Freeze drying IS sublimation.

    If it's frozen, then the water has very limited mobility through the piece. If it's cold but not frozen, then diffusion rates are also reduced.

    Look- wood will dry in the winter. If it's already dry then it may dry to a level below equilibrium that it would see in the summer, and may rehydrate a bit the next summer. That doesn't mean that fresh wood dries faster in the winter- which is sort of the question... I think. What the heck was the question again?


  24. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Rockey- Yup! Warm weather- faster drying. I'll stand by that- unless you happen to live where it just rains constantly I guess.
  25. Adios Pantalones

    Adios Pantalones Minister of Fire

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    "BTW, you can’t really use data from air-drying dimensional lumber to explain how firewood dries. Dimensional lumber dries mostly through the sides because its exposed surface area is almost entirely along the sides. Firewood dries mostly through the ends because it is short relative to its cross sectional area. Makes a big difference how stuff is cut."

    This one has been dispelled. I have dried enough 72" bow staves to know that it's not quite the case that the bulk of the wood dries through the ends. See tyhe pics that someone took of split oak drying that are currently up- you can see the wet portions!
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