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freeze dried

Started by etat, April 18, 2004, 07:17:37 PM

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etat

Saw elsewhere, and mentioned here a bit about putting wood in the freezer to dry.  Sparked my curisioty and just thought I'd ask about it.
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

Brian_Bailey

ck,  
The process is called sublimation.
The water goes from a solid (ice) to a gas without going thru the liquid state.
I always thought that it was a rather slow process and not as fast as suggested on the other forum.
But, who knows.  My wife temporarily put a halt to any experiments with the freezer in the house.
WMLT40HDG35, Nyle L-150 DH Kiln, now all I need is some logs and someone to do the work :)

Norm

I wondered how much moisture we would lose in some white oak we sawed last fall and stickered in an enclosed shed through the winter. Was hoping it would freeze dry some out but checking with a moisture meter showed almost no moisture loss through the winter.

beenthere

Norm
Do you think it is below 30% moisture content?  If not, will a moisture meter give an accurate reading for anything above 30%?  

Back some 30 yrs ago, I'd heard of research to dry (or attempting to) walnut gun stock blanks by freezing. Seems it was just pre-freezing before conventional drying, trying to find a way to shorten the kiln schedule to less than 7 months.  Runs in my mind it was done in Carbondale, IL  (can't find any information on it yet).
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Norm

If I remember right I checked it in late December and then a couple of times throughout winter time. It did lose a few points of moisture level but not much. Nice thing about cutting white oak in the fall is it loses moisture very slowly in our enclosed shed.

Your right in that it won't measure accurately above 30% beenthere, I usually don't pay any attention to the meter until under that. My experience in drying wood is best described as advanced rookie... no make that unadvanced rookie. :D

Ianab

My understanding of freeze drying is that it involves a vacumn, well at least thats how freeze dried food is made. Just leaving something in a freezer, well that old steak thats been sitting in the back for 12 months is a bit dry around the edges, but it's no where near kiln dried yet. I believe water sublimates from ice to vapour much more readily at low air pressure?

Anyone keen to build a refrigerated vacumn kiln?? :P
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

old3dogg

I just dont understand how you would move frozen vapors away from the wood ???

Den Socling

Mike,

The vapor is not frozen. Even when the water molecules are frozen, the ones that are close to the atmosphere can occasionally 'bounce' in the direction that releases them from the bonds that hold them together. That molecule is then in vapor state.

In a vacuum, it takes less of a 'bounce' so more break free.

Den

old3dogg

Okay.I guess I understand that part Den.
Tell me how you would move frozen water from the center of the wood.
I just cant believe this would work to dry wood.
Mike.

Den Socling


old3dogg

Put it to rest then!?
Lets talk vacuum drying with heat and all of that good stuff 8)

sawmillsi

hi guys,

instead of just putting it down, why don't you try the method (i posted it on the other forum).

we have and it works great.

why does it work - i don't know ( and i'm studying a bach. applied science - forestry), but just cause i don't know how it works dosn't stop it from working.

old3dogg

Okay.If it works than lets give it a try.
How do we go about it then?
Hey!I use to dry wood in an RF kiln so I will try anything once.
This stuff interest me to know end!

Buzz-sawyer

water is strange stuf...has ayone ever conducted the physics 101 experiment:
Place water in vacum

as pressure approaches absolute vacum the water BOILs and FREEZES at the same time a sight to see! :o :o :o :o

So in in a vacum freezer .....
the change of states is affected accordingly  8) 8) 8)
    HEAR THAT BLADE SING!

old3dogg

Buzz.
An absolute vacuum?
Do you mean like 0 Torr?
I have seen sap boil out of hard maple at 35 torr with no heat.
What kind of chamber does it take to pull an absolute vacuum?

Brian_Bailey

sawmillsi,  

I'm all ears to hear about the method your using.

I'm looking for a quicker way of drying carving / turning blocks.

Thanks  :)


WMLT40HDG35, Nyle L-150 DH Kiln, now all I need is some logs and someone to do the work :)

Buzz-sawyer

Old3dogg
 the term is APPROACHES ...the trick is the magic and very near temperatures of freezing and boiling...but the atmospheric pressure is reduced changing the boiling temp (vaporization)212f and the freezing solid state temp. 32f
....the two temps got closer as we approached vacume magic was when the two intersected.....dont recall specific atmospheres of pressure to be sure it was not absolute! (as in outer space)
    HEAR THAT BLADE SING!

Ianab

OK.. there is obviously something in this. :P
Theory... the freezing disrupts the cell structure, as the ice forms it expands slightly, maybe opening up the cell wall and allowing the water to escape faster? I don't know if this is correct, but it might explain what is going on... ???
As this seems to work at normal air pressure I might just have to get a couple of sample blocks in the freezer and see what happens.
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Den Socling

To get water to boil and freeze at the same time, the pressure around the water needs to be around 4.6 Torr.

Brian_Bailey

Below is a link that explains the process of freeze drying.

Looks like a complicated process that would need tight controls to achieve consistent results  :).

http://home.howstuffworks.com/freeze-drying2.htm

WMLT40HDG35, Nyle L-150 DH Kiln, now all I need is some logs and someone to do the work :)

old3dogg

Thanks Brian.
It all sounds interesting but it would be a slow process in drying wood.There is a lot of water in wood.
Mike.

Brian_Bailey

Last fall I sawed out some 12 & 16/4 x RW butternut for carving.
I stickered them O/S under cover.
I live in WNY so since Dec. the outdoors temps. have been alternating between a freezer and a refridgerator.

This AM I pulled a cant out of the stack and cut it in half.
This is what I found after a good 6 mos of air drying.
The shell tested 14%mc and the core was 34% or at least that is what my meter said.
Just looking at the core shows it to wet for carving..



I'm not trying to be confrontational, I just don't see how putting a chunk of wood in the freezer for a couple of days and then in the fridge for a week will give you dry wood.
If it can be done, I would certainly like to know the method  :D :D.
WMLT40HDG35, Nyle L-150 DH Kiln, now all I need is some logs and someone to do the work :)

Den Socling

Brian,

It can be done with a very strong vacuum. The atmosphere over your head is putting the pressure equivalent to a 760 mm column of mercury on your body. What was it that I said this morning? 4.6 Torr? That means that you remove all of the pressure except for 4.6 mm. If we did that to you, you would be a messy cloud drifting off into the sunset.  :o

Den

Buzz-sawyer

Old3dogg
We used a small4-6inch glass dome, on a rubbere matt seal.....using a small, loud, annoying vac. pump...
    HEAR THAT BLADE SING!

Brian_Bailey

Den,  

I've long been accused of being the source of smelly clouds drifting along. I've always denied any involvement, but me thinks that it's a fermentation /pressure release process :D :D.

But seriously,  I have a good market for carving wood and lately there has been a lot of interest for turning wood that is dry enough that it won't crack and distort before you can get it off the lathe.
If I can substantially cut the long wait between wet wood and dry, maybe my business could turn a profit  :D :D.

When someone posts a method for quick drying, I'm very interested in hearing about their method.

But on the other hand, I'm not interested in spending dollars to save nickles  :).

WMLT40HDG35, Nyle L-150 DH Kiln, now all I need is some logs and someone to do the work :)

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