Hi all,

Read this topic, but it seems old though:
http://www.refrigeration-engineer.co...a-Freeze-dryer

I’ve been reading up on different sites about freeze drying, I’m trying to figure out if a freeze drier for food can be made for something around 1000$. Just toying with the idea basically, so I was wondering if someone can correct me on the basic idea of how it works and if it’s doable in the way I imagine it.

Thinking of something like 2-3 cubic feet volume chamber for the chamber.
First off the high-strength pressure vessel part I totally understand, so what`s needed is a strong steel casing with an airtight lid, good gas-tight tubing etc, this part is clear. I`m thinking stainless or there abouts.
Looking around at eBay I found a number of vacuum pumps for HVAC, some of them in the 200$ range with two stage rotary vane pumps that deliver 0.05mbars at 3CFM.
The two questions I have about those kinds of pumps is this: can they handle moisture well, and does anyone know of a stainless version perhaps?
Second, what CFM should I be looking for, the chamber size of 2-3 cubic feet taken into consideration?

I`ve read that the super-cool coils in freeze driers are to condense\freeze water molecules sucked out of the dried materials, and they are mainly to keep the pump moisture-free. Is this a “must” just against corrosion? I`m asking because I`ve seen a picture of a freeze drier that has an external moisture trap, like a modular design where the trap, pump, and chamber are separate units. And also, will moisture in the pump reduce its efficiency significantly during the drying?

Now for the products being dried; at what temperature would they have to be frozen, and kept frozen during the process? This is a puzzling thing for me, because like I said before some driers have external moisture traps.

I`m probably missing something here, mind you I am no HVAC tech myself (work with electrical systems and automation), so forgive me for any misunderstandings.

Ps:
Thinking of the the moisture trap, I’ve read that even using common refrigerator compressors won’t quite do it as far as temperature goes. Some say in series maybe. I though of a compressor with a heat exchanger that would pre-cool the second (final) compressor’s condensed coolant fluid before it reaches the evaporator. Does that sound plausible or what?

Any replies are highly appreciated.