Ultra low freezer

[IvanZ]

Dear all,

I have been reading your forum and have read a lot of useful information. I am also working on the production of ultra-low temperature chambers. Until now we have reached -85C with a two-stage cooling system. The first stage is cooled with water at a maximum temperature of 45C, condensation of the first stage. The first stage evaporates at -30C, which is the condensation of the second stage, which evaporates at -85C.

We want to develop an application with -110C so we are wondering if we should continue with the same principle - if there is some gas mixture that we could use to gain -110C ? Or would it be better to start all over again and go for the autocascade system ?

Thank you,
Ivan

[Rob White]

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Hello IvanZ

A long time ago I helped with a project for cooling metal components in a chamber down to those
types of temperatures and instead of a triple cascade system they used a pressurised chamber with
a blend of refrigerants inside. It almost worked like an absorption fridge but at lower temp's.

Anyway there was one compressor that had a normal air cooled condenser and an evaporator inside the chamber.
This used one of the blends of refrigerant set at a certain suction pressure and temperature.
This then set off a cycle in side the chamber of the blended refrigerants that circulated through
convection and created different temperature zones in the chamber.
The refrigerant was taken from the chamber at different heights and temperatures and it created the lowest temperature to be -120degsC from memory

I want to say it got colder than that but it was more than ten years ago .
I also can't remember the blend of refrigerants but I do remember a consultant calculated
the exact blend by weight and it was a critical charge of 3 blends.

Sorry I can't be of much use but it was for a special project done by the wholesaler HRP in the UK.
HRP are now owned by Beijer Ref in the UK so maybe they might be able to help?

Regards
Rob

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