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

LLigetfa said:

I haven't seen this much junk science before.

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Battenkiller said:

LLigetfa said:

I haven't seen this much junk science before.

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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.

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Battenkiller said:

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

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Bigg_Redd said:

WTF is "P-Chem"?

I thought Chem stopped at "O"

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Battenkiller said:

Bigg_Redd said:

WTF is "P-Chem"?

I thought Chem stopped at "O"

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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.

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iceman said:

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??

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gerry100 said:

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.


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

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Battenkiller said:

gerry100 said:

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.


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

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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. .

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Battenkiller said:

Bigg_Redd said:

WTF is "P-Chem"?

I thought Chem stopped at "O"

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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.

.

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