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Frost Free Lab Freezer

Use a dry gas feed to eliminate frost build up
  [vote for,

The -80C lab freezer is something of a standard feature of medical/bioscience research lab. I use them for stable storage of tissue/protein samples, DNA archives, transgenic bacterial archives, sensitive chemicals & the good vodka. One problem in a busy lab is that frequent opening leads to moist room temperature air making it's way inside. This immediately forms a layer of frost and accumulates as inches of snow in available gaps. It coats almost everything making the labels difficult to read. You solve this by wiping away the frost on your box of choice, often partially melting it. Now your frequently used box will begin to develop a much tougher layer of solid ice. Labeling is lost behind layers of this ice, label tape falls off everything at this temperature, nothing writes on a very cold frosty surface. Existing ink, even specialty stuff is easily rubbed off plastic surfaces.

Ultimately a poorly maintained freezer will build up enough ice to compromise the seals and accelerate failure. This can happen in a few weeks. So how to mitigate this?

The problem is humidity in the air. We can remove that by moving all freezers to the antarctic, or mountain peaks, aggressive air conditioning or dehumidificaiton. These aren't practical for obvious reasons - noise and the coffee supply situation for example. What we can do is preferentially fill the freezer with a totally dry gas. Labs often have inbuilt vacuum, natural gas and crucially a nitrogen supply. A regulator on the freezer would allow a small constant flow of N2 into the rear of the freezer. This would ensure net outward movement of gas through the valve in the door that exists to compensate for temperature-induced pressure changes. This should mitigate a most of the humid air influx.

If a nitrogen line isn't available, cylinders can be used. A further opportunity exists to use liquid nitrogen. Many labs have this constantly on hand. A port in the freezer would allow a weekly top up of liquid nitrogen into a vacuum-insulated chamber. The liquid slowly boils off and supplies the freezer with it's dry gas feed. Filling liquid nitrogen cell-storage is already a weekly chore, so this is a modest addition.

bs0u0155, Jun 03 2020


       Why only for lab freezers? Have sympathy for users of domestic installations
pocmloc, Jun 03 2020

       I like it. It is a step more convenient than filling the entire lab with nitrogen.   

whatrock, Jun 03 2020

       //more convenient than filling the entire lab with nitrogen.//   

       That has it's appeal though. There are lots of chemicals that are oxygen sensitive, a nitrogen atmosphere would be a robust guard against fire and undergraduates. As a downside, the bunsen burner wouldn't work, and you can't really do science without one of those available.
bs0u0155, Jun 03 2020

       I was thinking a glovebox/airlock system to minimise moist air transfer, but this is much better!
As per [kdf], could you use a convenient 79/21 mix of nitrogen & oxygen instead, or is that getting too complicated for the temperature control side of things?
neutrinos_shadow, Jun 03 2020

       I'd keep the nitrogen flow relatively modest. It will likely not bother a standing person anyhow, for an upright freezer, when you open the door, the cold nitrogen, just like air, will just sort of slump downward and spread over the floor. You can feel the effect on bare feet if you open a freezer. It CAN displace oxygen, but this isn't the same level as, say spilling liquid nitrogen in an elevator. Most labs have a howling gale blowing through them anyway, just because of multiple fume hoods extracting air. Now, if you put your head RIGHT inside a chest freezer, it might end badly, but that person has bigger problems.
bs0u0155, Jun 03 2020

       air curtain ?
FlyingToaster, Jun 04 2020


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