Refrigerant Mixtures -150C

Hi guys,

I'm new in the refrigeration area, and I do services with -80C and -150C ultra-freezers.

I've tested some refrigerants like R-1150 in the -80C 2nd stage and it worked very nice.

Now I want to test a -150C. It uses a mixture of five refrigerants, to get -11C, -26C, -84C, -128C and -160C in the evaporator.

The question is: can I use just ONE refrigerant instead of these five, like R-50 (Methane) or R740 (Argon)? Do I need to make a cascade system?

Obs.: the system in question have a Copeland scroll compressor.

IMO, a semi piston compressor is better.....

Hi Ernestlin.

To use a single gas would be more or less impossible due to the problem to condense the high pressure gas. The single stage you mention has a hard working condition and I have seen a lot of laboratorie chest freezers give up after a short time. Scroll is not a good selection for those excessive pressures on such systems. The only brand I have seen who can cope running for 10Years or more is Sanyo units. They use a dobbel first stage heat exchanger to make a better condition for the second stage 5 gas mixture. Earlier days they used hermetic compressors on both stages, but later on they changed to a half hermetic on the second stage specially made for the purpose. It is gone quite some Years since I was into repairing them, but I can remember that the pressures they have to deal with is pretty wild. Still with two stages, the low stage was taking a lot of stress. The pull down is always a problem due to the amount of gas who still not is condensable before many hours of running time. The low stage on a -135c from them had a high pressure cut out at 32bar who actually had to cut in and out for quite some hours in just some minutes of interwalls to get on with the condensing as here in 3 secondary heat exchangers.
The single stage units have to do the all over just one compressors and seems to never cope with that over too many Years.
Anyway, whatever you want to test on such units, stay away from attach service manifold on them without you have an urgent need to check pressures.
If you loose a few gram of refrigerant in the second stage you are into deep trouble.