Freezer colder than -20C, but warmer than -80C

[Tom De Medts]

Dear all,

Is it possible via DIY engineering to design and build

a freezer that is colder than -20C, but warmer than -80C.

-20C freezers are relatively inexpensive

and 

-80C freezers are way more expensive, also large in size, requiring maintenance plans

I want to know whether there is something in between.... 

Thanks! 

[Dakota Hamill]

No idea, but would honestly love to know out of all the temperatures
that could have been chosen, why -80C and -20C are the standards.

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[S James Parsons Jr]

Make a liquid nitrogen generator

Sent from my iPhone

> On Apr 12, 2021, at 7:02 PM, Dakota Hamill <dko...@gmail.com> wrote:
>
> No idea, but would honestly love to know out of all the temperatures

> To view this discussion on the web visit https://groups.google.com/d/msgid/diybio/CAGdeWmQ%3DW%3D75VdqcGFaF3iAFFkHzOSEFiF5BSMTuSM-91tQPrg%40mail.gmail.com.

[Cathal Garvey]

Almost certainly something to do with optimal phase transition behaviour in common refrigerants, I'd say. I would imagine that -80C is more attractive than -40/-60 also because it freezes water rapidly enough to skip a few of the more damaging ice crystal types, but ultimately I suspect it's just an economy thing. As well as compatibility with the temperature of dry ice, which is either used for transiting frozen goods or as a backup/band-aid for failing freezers.

In some places one can just buy dry ice easily enough, which presents another possible route to accessing mid-range temperatures if combined with different bath fluids - when combined with acetone it can go down to nearly -80C but a combination of different fluids, or minor electronic contrivances to control airflow around a bath, could allow control between -80 and -20. Probably.

Just watch out for condensing ice build-up with custom-built rigs. This is a problem even at -20C and it's why most modern freezers have an antifreeze cycle (which is problematic for home labs because it exposes enzymes and cultures to regular temperature spikes). I've never built a refrigerator but I imagine this is one of the harder engineering problems to solve without relying on regular defrost cycles. Perhaps a silly-but-practical route would be to build two of the same rig and just alternate them to permit regular defrosts.

13 Apr 2021, 00:02 by dko...@gmail.com:

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[Tom De Medts]

Have you or someone else constructed a liquid N2 generator successfully?

I don't suppose you are suggesting building something similar in sophistication to one from a commercial brand (which seem to go for ~2.5K minimum)

(An exception was this item on Ebay for < 1.5K which is still a little more than what I'd want to pay without knowing this is 100% going to work for at least a few years' time)

OR

Are you suggesting something more rudimentary in design, but perhaps nearly as effective as the more fancy ones?

From this example YouTube link, my understand is that I'd need at the very least these components:

• air compressor
  
• nitrogen filter - filter sounds expensive....
  
• cryo pump - most pricey?
  
• liquid N2 dewar (I have that already)
  

hmm.... those together will easily cost > 1.5K.

So, perhaps I should stick with buying liquid N2 from my local AirGas or Praxair branch? :)

Which happens to be much cheaper than using dry ice....

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[S James Parsons Jr]

https://homemadeliquidnitrogen.com/scrubber.html

Sent from my iPhone

On Apr 14, 2021, at 12:42 AM, Tom De Medts <tdm...@gmail.com> wrote:



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[Cathal Garvey]

Obligatory warning, that Liquid Nitrogen can be quite dangerous for two main reasons:

• Super cold
  
• Asphyxiation
  

..so it can be a risky thing to work with at home especially in settings where someone might have a little lab in a small back-room with inadequate ventilation for Nitrogen.

Note also that asphyxiation due to an anoxic environment can occur without any sensation until you simply lose consciousness. The feeling of "gasping for air" is the sensation of CO2 build-up in the bloodstream, but if you are breathing oxygen-free gas such as nitrogen or argon, you will not feel that you are asphyxiating and will simply pass out and die.

In fact, argon asphyxiation is widely considered the most humane way to euthanise research animals.

So, take DIY nitrogen, either produced by a professional company or made at home, as a somewhat risky route for home refrigeration.

Dry Ice can also lead to asphyxiation but with dry ice, you'll know it's happening because it's CO2! Though, by the time you feel the asphyxiating effects of CO2, your brain will not be working very well so you may be prone to making mistakes and failing to mitigate the risk as well as you thought you would. So bear that in mind, too. At least until you get CO2 poisoning and stop bearing it in mind, that is.

Gasses: nature's answer to scientists.

14 Apr 2021, 11:49 by sjamesp...@gmail.com: