Wood "Freeze" Drying ?

Willhound Posted By Willhound, Nov 24, 2005 at 4:34 PM

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  1. Willhound

    Willhound
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    Nov 20, 2005
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    It gets extremely cold and very dry here in the winter with relative humidity levels sometimes down into the 60's.

    I have heard it expressed that because it is so dry, it is possible for the moisture content of wood to drop, or in other words, for the wood to dry out over the winter months. The only difficulty I have with this is that I would think that if the moisture content in the wood is frozen, it cannot be removed from the wood ?
    On the other hand, I have seen circumstances where I've had snow or ice in my unheated garage and with no access to wind etc. and over the course of a few days the ice or snow will "disappear", therefore I assume it has evaporated. Same thing as if you leave ice cubes in the freezer long enough, eventually they start to lose mass.

    Any of you more scientific types out there care to express an opinion?

    Willhound.
     
  2. Dozerjim

    Dozerjim
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    Nov 19, 2005
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    As far as ice cubes losing mass I believe that is due more to modern day frost free freezers removing moisture. hmmmmmmm maybe i can store my firewood in a chest freezer.
     
  3. NWfuel

    NWfuel
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    Nov 19, 2005
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    I would have to say from 28 years of selling fuel in the Seattle area that it will lose it's moisture. we will have rain for weeks which soaks the wood. 2 weeks of mid teens to lower 20's and the wood is freeze dried. Sucks the moisture right out of it.
     
  4. Corey

    Corey
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    Nov 19, 2005
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    Wood will definitely dry in the winter. I think technically the term "freeze drying" is used when some article containing water is frozen, then a vacuum is applied so the water ice can transform directly into a vapor - process called sublimation. Under normal atmospheric conditions, the ice would have to melt first. I suspect that what seems like "freeze drying" at normal atmospheric pressure is actually a slight melting of the ice, but not necessarily enough to leave a puddle or traces of water visilbe to the unaided eye, followed by evaporation.

    I would also suspect all the wood really cares about is relative humidity. If you have a 95 degree summer day with 90% RH, there may not be as much drying going on as a 35 degree winter day with 30% RH. I suspose the wood could also dry if the air temp were below freezing if the wood happend to be in the sun or have some other way to pick up a bit of heat.

    Corey
     
  5. Mo Heat

    Mo Heat
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    Nov 18, 2005
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    Equilibrium moisture content (EMC) of wood in an outdoor environment depends upon both temperature and relative humidity. Judging by the EMC of wood in Alaska in the coldest months, I think it implies wood can somehow sublimate moisture, otherwise fresh cut wood could never obtain these EMC levels when it is frozen solid.

    I got this link from Marty last year and found it interesting. Page 7 starts the table of measurements.

    http://www.woodweb.com/knowledge_base_images/zp/equilibrium_moisture_content.pdf
     
  6. wg_bent

    wg_bent
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    For what it's worth, the process of sublimation will occur without a vacuum. If the temp is well below freezing for several days, did you ever notice the ice on your porch, drive way, etc... goes away, yet it definitely didn't melt. Ice cubes in a freezer will also show this principle.

    Moisture frozen in wood even at depths in the wood will sublimate. Probably at a slower rate than a warm summer day, but that would take a government grant and several million dollars to study.

    Warren
     
  7. Willhound

    Willhound
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    Nov 20, 2005
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    Neat report, Mo.

    Warren, you are exactly correct! A government grant for several million $$$ should just about do it. I'll start on the grant application, but one of you will have to submit it since I'm one a them "dang foreigners". I figure a couple of million should allow us all to meet somewhere cold along with way too many cases of beer (the strong Canadian stuff, of course) and sit and watch a wood pile sublimate. Someone will have to bring their moisture content thingamabob and take a measurement now and again.

    Are you in?
     
  8. BrotherBart

    BrotherBart
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    Somebody bring the Moosehead and I will bring the moisture thing-a-ma-bob.
     
  9. wg_bent

    wg_bent
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    I am soooo in!!!!
     
  10. Mo Heat

    Mo Heat
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    Nov 18, 2005
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    I'm there, dude. I'll take readings from the thing-a-ma-bob as long as the beer holds out.
     
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