woodgeek said:
If there were no binding energy it would dry out completely (eventually).
It will, and without any added energy needed to drive the process. Any RH/MC chart will show that the EMC of wood at 0% RH is 0%. The problem becomes getting the air down to 0% RH.
On everything stopping below 32F: The pore water will freeze into ice at 32F, but it will still sublime at the previously liquid/vapor interfaces. The vapor/ice partial pressure at 31F and the vapor/liquid pp at 33F are basically the same, so the drying rate of pore water should not change by much on freezing. Moreover, the adsorbed water isn't ice below 32F, its still adsorbed water. The water molecules are touching the wood, not each other, and so can't form an ice crystal. There is no reason why their mobility or vapor pressure should do anything special at 32F either. I get your water crystals breaking the the structure thing, which is intriguing, but do you have any evidence? Can't wood fibers be stretchy enough to accommodate the strain?
How will the water bound into the cells sublime once the RH of the air deep inside the wood rises to 100%. It will happen, but at a greatly reduced rate compared to sublimation occurring at the surface. A moisture gradient will soon be established as water molecules start to leave the ice inside, and the most saturated air will be that closest to the fibers themselves. Yes, molecules will diffuse into the intercellular spaces and longitudinal tubules, but without a rapid exchange of air like is found at the surface, little sublimation will occur by comparison to the outer surface.
The damage to the cellular structure in wood is a well documented phenomenon. There is mention in the literature of this occurring in live trees as well, but in the live tree there are mechanisms that help mitigate this. I had about a face cord of green cherry stored next to my stove over the Thanksgiving holiday. When it was half gone I brought in replacement wood that had received a deep freeze during the second week of December. The replacement wood was already checked in the ends (hey, if it's not drying out there, the checking must be from freezing damage alone) when I brought it in, but after about 4-5 days it exhibited a very deep checking of the end grain, much deeper than the wood stored in the basement for several weeks more. You could actually see the diagonal line that separated the old wood from the new in the stack, the new wood looking severely checked in the ends although it most likely still contained a higher moisture content.
On the end/side drying issue--I think we all know that split wood dries faster, so there must be some drying out the sides. I saw a study once (can't find it) that said the diffusivity of water is 4x higher along the grain than across it, so a drying front would move in from the ends 2x faster than from the sides (its a square root of D). Not a huge difference. The cracking ends are due to the shrinkage being across the grain rather than along it (as lots of folks here will confirm). So, once the wood piece is more than couple times longer than it is wide, that guy will dry as much through the sides as the ends. That square root business also explains why a 'plank' that is much thinner in one cross grain direction dries so much faster than a square cross section--splitting a square into two planks should dry 4x faster, into 3 equal planks should dry 9x faster etc.
It's nice to know that we have a person on board with a PhD in applied physical chemistry, but I got to thinking, Gee... what if we could consult a guy with a PhD in wood technology. He might really be able to answer this question.
Then I remembered about a little known book called "Understanding Wood", written by a dude named Bruce Hoadley. I was in town this morning and decided to finally buy a copy of the book at the local Barnes and Noble. Here's what Mr. Hoadley has to say about the subject in Chapter 6 "Wood And Water":
... on page 130
"But perhaps the most universal problem is end-checking. Water moves longitudinally through the wood
10 to 15 times faster than it moves perpendicular to the grain. Therefore, end-grain surfaces rapidly lose their moisture and are the first to drop below FSP [fiber saturation point] and begin to shrink. If the shrinkage exceeds 1.5%, tension failures in the form of end-checking may occur. Here's another way to look at it: let's assume that moisture moves on the average 12 times faster along the grain than across it. Suppose a board is 1" thick.
Up to 6" from either end, water molecules at the mid-thickness of the board have a better chance to escape through the end-grain surface than through the side-grain surface. Except for the 6" inches near the end, drying from the board should be uniformly slow because most molecules will [have to] escape through the side grain. The objective of end-coating boards with sealers is to prevent rapid end-drying and create side- grain drying right to the end of the board. Stresses are ever-present in drying because there must be differential drying in a piece of wood to make moisture move. If the moisture gradiants are great enough, serious defects will develop."
So, Mr. Adios might better come to me for the fly tying lessons (I used to be a commercial tier) and seek wood drying advice from Mr. Hoadley when next they meet.
Sorry to those who hate long posts....
Don't apologize to me, I'm a wordy SOB myself. I really appreciate all you have pointed out. Others are pointing to the work done on long boards (almost entirely cut 4/4 BTW) even though we are talking about short sections split rather thickly by comparison. You have obviously taken the time to explain what you know in a way that any of us here can figure out, giving mechanisms that describe the actual movement of water. You have added to my knowledge base. I hope I have added some to yours.
BK