Home-made Freeze Dryer

[Bigun]

So I have been mulling over in my brain how to build a self contained freeze dryer, with computer controls that monitor moisture, temperature, and pressure levels.

 

From what I can gather. freeze drying is all about sublimation.  Basically, I have to get the item around -25 C, drop the pressure, and then slowly begin warming the environment, and the ice should sublimate into vapor, leaving the item's structure intact.

 

My goals:

1. Self contained - I don't want to have to babysit the unit, adding any chemicals to the system to keep things running.  Most of the cheap homemade one's use dry-ice/alcohol to achieve the ultra low temps needed.
2. Computer controlled - during the process, some variables will need to change for optimal drying
3. Homemade - I can buy a pre-fab unit to do this already, although it costs about $3,500
4. Cost:  I'd like to see all this built for less than $500, but I don't see how this is possible.  Hence why I'm even here.

A few challenges:

1. Freezers capable of -25 C are very expensive.  The only other way I've seen this done is using ethanol alcohol in junction with a water cooler
2. Excess moisture has to go somewhere.  I see only two ways out of this:  1)  Find a vacuum pump that can pump out moisture.  2)  Create an ice trap chamber that drops to -70 C and traps the ice.  So either another even more expensive freezer or a specialty pump.
3. Finding sensors that the Pi can use.
    

As it stands, I see know way of getting this done without the cost going into the stratosphere.  However, if it could be done, oh man... the mountains of freeze dried ice cream we could make.

So, ideas?

[Huntsman]

Why Rpi? A 3 buck microcontroller could do the job fine.. 1/10 the cost..

[Bigun]

This isn't even on paper at this point.  Sure, a microcontroller.  We have bigger mountains to jump at this point.

[Unimportant]

4 hours ago, Huntsman said:

Why Rpi? A 3 buck microcontroller could do the job fine.. 1/10 the cost..

And more stable. A Rpi is a full blown computer running a complex OS, a crash every once in a while can happen. I've got loads of AVR's in the field and they're extremely stable, i'm sure the same goes for other microcontrollers.

[Hackentosher]

More importantly, why do you want a freeze dryer? 

[Bigun]

8 hours ago, Hackentosher said:

More importantly, why do you want a freeze dryer? 

A few reasons.  I like experimenting with food, I like to prep and store food, and most importantly:  freeze dried ice cream.  If you've never had any, I would highly recommend finding some, try it, and get back to me.

[MrLau]

Have you  watched Applied Science video on his freeze drying, if not they are worth checking out

 

 

However I think you will need some form of cold trap, which might require a pretty expensive dual stage pump to keep cold, if you don't want to use dry ice or liquid nitrogen.
The computer control will be pretty easy compared to all the other stuff you have to make. So I think your focus should be on getting it to work manually first, and then automate it later.

[Huntsman]

Now I'm interested in this project..

[Bigun]

11 hours ago, MrLau said:

11 hours ago, MrLau said:

Have you  watched Applied Science video on his freeze drying, if not they are worth checking out

 

[Videos Removed]

 

However I think you will need some form of cold trap, which might require a pretty expensive dual stage pump to keep cold, if you don't want to use dry ice or liquid nitrogen.
The computer control will be pretty easy compared to all the other stuff you have to make. So I think your focus should be on getting it to work manually first, and then automate it later.

Yes I have, in fact one is linked in the OP.

All points, agreed.  Just locating the parts within a reasonable price scale I see as the biggest challenge.

[MrLau]

You might be able to use silica gel to dry the air instead of a cold trap, it will of course have to be dried out when they have absorbed all it can, but it could be a much cheaper alternative if you could make it work.

[Silverwolf_7]

You could make this bigger...