Sub Zero Temperature Chamber (around -50°C.)

[TheEngineeringWay]

Hi Guys, Thanks for looking at the post firstly.

I'm in the process of creating a chamber roughly around 30mm x 50mm x 70mm (W, L, H). The chamber will be used below the typical refrigeration temperature (-18°) of around -50°C.

Please could you offer some advice where to start with this.

1. How can the cooling be achieved?
2. Any suitable pressure tight/ insulating chambers (e.g fridge)..what do you recommend?

I have looked at CPU cooling using liquid nitrogen, but temperatures are well below what I need it to be, and also, the sizes are quite limited..

 

[Twigg]

-50C is too warm for cryogenic cooling, as far as I know. If you can't use liquid nitrogen for whatever reason, then you will need some form of refrigeration. Alternatively, it may be easier to simply vent cold air from a liquid nitrogen dewar over whatever you wish to cool. This sort of convection cooling mechanism will probably be cheaper and easier to implement than refrigerating. Keep in mind that if the pressure of this flow is not sufficiently high, then humid room-temp air will drift in, and water will start to condense on whatever you are cooling and the air will warm the chamber. Hope this suggestion is helpful.

 

[russ_watters]

Dry ice is -79C.

 

[berkeman]

At my work we use Sun Electronics ovens to do temperature testing, which includes -50C and below:

http://www.sunelectronics.com/Temperature-Chamber-EC1X-Model.html

We use liquid CO2 systems to achieve the low temperatures and 10C/minute temperature ramps for reliability testing protocols, but I don't know if you can achieve -50C with slow refrigeration systems or not (I'm an EE, not an ME -- call Sun for technical advice).

How steady do you need to maintain your low temperature? If you need it to be steady to within a degree or two, you will need a good closed loop system like you get with commercial test ovens. If you don't need tight control, then maybe solid CO2 (as suggested by Russ) plus an arduino ventilation system might work.

 

[rbelli1]

ThermoKing Super Freezer refrigeration units can keep a 40' container at -60C using a two stage refrigeration system. The first stage is a standard R-134a refrigerant reciprocating compressor. The second stage is a R-23 scroll compressor. You don't need anything that size but you should be able to find suitable equipment if you need long term continuous refrigeration at that temperature.

BoB

 

[Baluncore]

Welcome to PF.
You have not specified how much thermal power will need to dissipated.

Quality Peltier thermoelectric cooling elements can make a difference of 50°C in one module. Cheaper consumer Peltier cooling elements can operate easily with a 20°C temperature difference. If you place one or more Peltier cooler stages inside a conventional freezer it should meet your requirement.

Alternatively, use a balloon, aircraft or mountain to rise above 25,000 feet.