OK Kow It Alls...OT to the bone

Apr 17, 2021 Last reply: 5 years ago 6 Replies
J

I want to freeze dry tings. It does not take a perfect vacuum, and it seemed when I had access to one from a fridge it would probably do the job.



Now this does not go in the freezer, the vacuum s*it happens when it i out ad thawing. You need low enough air pressure to force it to subliminate, bypassing the liquid state altogether.



I have been trying to get an old one and now maybe a dehumidifier one would work.



The EPA regs on that s*it frigged that all up. So now I can get a WORKING dehumidifier for about what I would have paid or compressor of the street. Even the scrap metaal joint wcn't sell me one even though it definitely has no Freon in it.



If the dehumidifier will work, great. Case closed. If not, well then what ?


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B

Actually, all lowering the air pressure does is to make it easier for the water vapour to get away from the object you are freeze drying.

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gives the vapour pressure of water over liquid water and ice over a range of temperatures. It's 4.5840 mm Hg at 0C . If you can keep the pressure over what ever it is you are drying appreciably less than this, all the gas molecules around will be water vapour, and whatever it is you are drying will dry as fast as you can replace the latent heat of evaporation.

You do want to pump out the non-condensable gases. Anything that gets them below a couple of mm of Hg should work fine. Catching the water vapour in a cold trap rather than letting it get into the vaccum pump can be a good idea.

Probably wise, since you don't seem to know all that much about what you are doing.

The humidifier can dehydrate, but it won't freeze dry, and it won't be quick.

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J

Why do you want to freeze-dry poop?

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B

He doesn't. He's just using a disparaging word to refer to the process of freeze-drying.

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J

Don't know tongue-in-cheek humor do ya, Bill?

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B

Not something that John Larkin goes in for. He does seem to be peculiarly sensitive to references to faecal matter. This can make hm unintentionally comical.

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C

I mentioned this before, it could explain a lot...

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