-150 Degree Lab Freezer

[barbar]

-150 is an autocascade. Single compressor (3HP scroll iirc) 4-5 different refrigerants in one system. The higher pressure gases act like non-condensibles in the air cooled condenser, after which liquid is dropped out through a cap tube to a heat exchanger that cools the vapor that didnt condense in the air cooled condenser, so on and so forth. At the end you have argon in a saturated vapor state going through the evaporator. I like working on them, most people run screaming. Mostly cause they don't want to do what the manufacturer says needs to be done to get it right...

Best description I seen for an autocascade, depending upon the age, it may also be a 3 stage cascade.

[cold in alberta]

there is a guy on here his name is ultralow787 and he great on this kind of stuff-he walked me through an autocascade a few years ago after a compressor change and the factory charge they sent was a bit off on the quantity of 134a,it was a bit of a head scratcher.

[Hvac216]

Interesting. I couldn't even begin to help you my refer exp little reach ins but is love to hear about this.

[CFESAmasterEGSR]

Barbar- I'm lost at the argon gas. Fascinated with this concept though.

[icemeister]

Autocascade systems are indeed fascinating. Here's a link to a past issue of Sporlan's Cold Wars written by Garth Denison which explains them quite well.

ColdWar February 2007 Auto Cascade

[Tommy knocker]

Haven't worked on these myself. Used to work for another shop that had 2 guys that did. Got to watch them play with them a few times. Attention to detail was extremely important to them. Usually had very detailed procedures they followed. Looked like fun.

[malcor]

I've done a bit of work on Edwards Cryodrive units, chilling an evaporator to about -450'F!

The most recent repair was to replace a locked compressor. It was an off the shelf Copland compressor but modified to be water cooled. Single stage system using Helium as the refrigerant.

I was quite surprised with the manufacturer's instructions for charging the system with refrigerant at the time. It was just two lines, Evacuate to 1 micron, Pressurise system to x Bar.

Also, the evaporator was a about 1" square and under high vacuum.

[Hvac216]

I've done a bit of work on Edwards Cryodrive units, chilling an evaporator to about -450'F!

The most recent repair was to replace a locked compressor. It was an off the shelf Copland compressor but modified to be water cooled. Single stage system using Helium as the refrigerant.

I was quite surprised with the manufacturer's instructions for charging the system with refrigerant at the time. It was just two lines, Evacuate to 1 micron, Pressurise system to x Bar.

Also, the evaporator was a about 1" square and under high vacuum.

What kind of application is that used for? What needs to be cooled to negative 450???

[malcor]

What kind of application is that used for? What needs to be cooled to negative 450???

This particular equipment is a S.E.T (Single Electron Transistor) depositor. They use it in R&D for the design of hybrid semiconductors. The design that they were/are working on at the time was some sort of photo transistor processor for telecommunications.

This S.E.T Depositor is located inside an ultra clean room along with a whole lot of other gear. To get in the clean room is a laborious task in itself, having to go through three stages of clean rooms and garments before getting inside the lab. And once inside there it is like a wind tunnel but the air going from the ceiling to the floor via stages of electrostatic and absolute filters. Quite noisy. I have some pictures of inside the lab somewhere on my computer. I was mostly taking them of the other really impressive looking equipment that they had in there.

Interesting place to work but a real PITA when you have to go from the inner lab from the control station and S.E.T depositor to the outer lab where the two Cryodrive units are located. Really painful, especially if your security swipe card gets left in one of the intermediate clean/changing rooms and you follow the professor into the lab then get stuck in there for over an hour because everyone’s gone to lunch. I was staring at the emergency exit button for a while, weighing up the repercussions of pressing it and thinking of good excuses...

[barbar]

Barbar- I'm lost at the argon gas. Fascinated with this concept though.

Argon = R740 and at atmospheric pressure boils at around -186C. (just another refrigerant)
So if you need -150C, you need a refrigerant that will boil below -150C
But is a fascinated subject.
I built a -196C freezer, for processing metals, I used air as the refrigerant, and a 3 stage air compressor.

[coolerik]

Yup, it was an autocascade system, a little intimidating at first but got it figured, low on gas based on the mfg "soak" test, which is basicly run it, shut it off and wait 10 min and compare pressure to their chart. Back next week to find leak and see what the mfx wants me to, probly change oil seperators, compressor and drier flush everything and recharge with the magic cocktale
Neat stuff

[coolerik]

Yup, it was an autocascade system, a little intimidating at first but got it figured, low on gas based on the mfg "soak" test, which is basicly run it, shut it off and wait 10 min and compare pressure to their chart. Back next week to find leak and see what the mfx wants me to, probly change oil seperators, compressor and drier flush everything and recharge with the magic cocktale
Neat stuff

[coolerik]

Oops double post