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Author: Subject: Chest freezer cold trap?
National Hazard

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[*] posted on 1-5-2020 at 05:37
Chest freezer cold trap?

Nowadays when chest freezers are available from 100$ upwards and they easily produce -30C and colder temperatures, I find it intriguing to purchase one, and create a round hole with replaceable lid to the top of it to be able to either directly place receiving flask into it, or make a deep, cylindrical flask that can be filled with sat CaCl2 solution that could be used as cold bath. The freezer would keep the liquid cold constantly during the whole operation.

Also, one could make holes for long coil placed inside the freezer to circulate cryogenic cooling fluid to jackets or wherever it's needed.

The freezer could be loaded with either ice or CaCl2 fluid so the thermal mass is maximized and fluctuations remain minimal during operation.
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International Hazard

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[*] posted on 1-5-2020 at 08:15

I am currently using a chest freezer to make and store blocks of ice
to chill water for recirculating condenser cooling water,
a few relevant thoughts :

1) chest freezers are excellent for storing stuff at low temperatures due to good thermal insulation
and the fact that cold air is not replaced by warm air every time they are opened

2) due to #1, the compressor does not need to be very powerful
i.e. the heat pumping rate can be quite modest.

3) due to #2, it can take days to freeze a significant volume of water
i.e. the heat pumping capacity may be much less than you expect.

4) you could replace the lid with a sheet of wood or expanded polystyrene and make your holes in that,
so that the freezer could later be restored to its original configuration if required.

5) if there is any water in the vapour(s) that you wish to condense
it may freeze in your pipework - blocking it to gas flow

6) if using very cold cooling fluid remember to not use higher b.p. liquids if using a glass/borosilicate condenser as the temperature difference may crack/shatter the glass

CAUTION : Hobby Chemist, not Professional or even Amateur
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International Hazard

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[*] posted on 1-5-2020 at 09:26

exactly what sulaiman said.
freezers and fridges don't usually have powerful cooling systems, because they usually need to just keep something cool, not actively cool something.

with a setup mentioned by you, you would really just relay on tge thermal mass of your ice/cooled fluid, it won't actively cool your system fast enough.

let's make an example, you want to use it to cool the water for a condenser during a distillation, if you are pumping 500w of power to the boiling flask, you need to get out 500w of heat from the vapour to condense it. a small fridge o chest freezer doesn't have 500w of heat pumping capacity.

that's why most amateurs use air conditioning units, they are made to work continuosly with a heat pumping capacity of even a few kilowatts.

also, if you run the compressor 100% of the time, it could overheat easily. they are made to run a few minutes at a time just to keep up with thermal losses through the insulation.

feel free to correct my grammar, or any mistakes i make

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[*] posted on 7-5-2020 at 12:10

Check this out, it might be more in line with what you're trying to do and it's essentially how laboratory specific "recirculating chillers" work. The benefit is that it's much more efficient because you're not chilling a liquid through an air interface (cold air in a freezer --> reaction vessel), you're chilling the liquid directly with the heat exchanger.

Here's an example of a commercial unit. You can see they pull 1000W at the outlet which is something like the power draw of a 10,000-12,000 BTU air conditioner.

[Edited on 5-7-2020 by monolithic]
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[*] posted on 14-5-2020 at 13:09

If you're not planning to use it regularly, dry ice is surprisingly cheap. Order from ice cream makers.
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