Freeze Dryer ?'s

[Mi. Mike]

A good friend of mine is a taxidermist and we got to talking about freeze drying not long ago.  He said he has looked at a few but could not spend the $$.  I am in the refrig. field and I was thinking I could probably build one with pieces and parts.
I have several ?'s though before trying to build one.  Here is a crude pic of one that I found


1.  The media to be freeze dried needs to stay above 32 deg?
2.  How deep of a vacuum needs to be achieved?
3.  Heaters on the shelving, electric?  How important?


Any input you all have will be appreciated
Thanks,
Mike

[cyclone]

Here's somethin to get you started!



http://wine1.sb.fsu.edu/chm1045/notes/Forces/Phase/Forces06.htm

[Mi. Mike]

Thanks for the link.  That will help.

Here is a vaccum conversion chart i found.
http://www.pauloabbe.com/productLines/vacuumDryersSystems/vacuumConversionChart.html

Does anybody know the exact temps the shelving & the box are running.   
Sounds like they try for 32 in the box but if 36  was seen would it be too much?  I cant see the heated shelving being much warmer than that either. 

[cyclone]

Check the chart I cited for the "triple point".   For pressures at and below the triple point (4.58 torr from an old chemistry book), water will go from the solid state to the gasesous state or "sublimate". 

To answer your question 1, No the speciman does not need to stay above 32deg F for the process to occur but, you have to go by the phase diagram again, at 32 and below you'll need stronger vacuum.  As long as the vacuum/temp combo keeps you below that triple point and to the right of the solid line, it'll work.

We have chambers at work that are kept at room temp.  Samples are frozen solid and put into the vacuum chamber.  Once it's pulled down to the proper pressure it's solid...First time I saw it I was flabbergasted..I thought it would thaw...Heating will speed up the process though..

Don't forget about your condensation chamber,the freezer.  The temperature will have to be cold enough for deposition, i.e. gaseous phase to solid phase, to occur.  You don't want the vacuum to be too strong or you'll pull all the water vapor through the pump...Pumps don't like water....

Luck,

[cindy110772]

Anyone know where in North Carolina I can learn freeze-dry pet preservation?