3 Stage -150c project by Gray

[Gray Mole]

Just as it says, I'm going to be working on a 3 stager. It's something I've been itching to do for ages now, and I'm finally ready and able to get a start.

I don't expect it to be that fast, but everything except the hand valves and HX's are here. I have one of each, but there's some on the way and they'll be here before I'm ready for them (I hope)

What I do have here is enough to do the first stage anyways, and that will take a bit of time. I'm fighting a seriously small space again, but I've measured up and it's going to fit. Just going to be really fiddly and IMHO well worth the extra work.

I made up a really small case from some stuff I had here. Just the frame right now, but I got some pics of things in place and how it'll go together.

Specs...

1 x 64LRA/16cc Horizontal Rotary - Tecumseh - Around 1hp or just under - 1st stage - 404a most likely - -45c or lower at 350w test (Target is -50c load)
(Was new, but I put it in the cooler I'd made for a guy from India and he never got back to me when it was done so I'll use it here. Was under the 20kg shipping limit for cheap shipping too)
1 x 48LRA/13cc Rotary - LG - 3/4+hp - 2nd stage - R1150 - -100c or lower at 350w test (Target is -105c load)
1 x 37LRA/12cc Rotary - Toshiba - 3rd stage - R50 - -140c or lower at 350w test (Target is -150c load)
1 x 14 plate 12" long BPHE 2nd stage HX - Should be roughly equivalent to 28-30 plate performance, longer makes the heat transfer far better.
1 x 20 plate standard 8" BPHE 3rd stage HX
2 x Temprite 304 oilseps with handvalve controls
40mm evap (Duniek or maybe older Piotres) with Braided 1m flex line
Condensor with dual 200cfm fans + Smaller desuperheater to be split for 2nd + 3rd stage w/100cfm fan
2 x 375psi cutoff switches

For the most part that's it for the major components.

I'm going to try to stay pure if possible on the 3rd stage gas. I may have to 'dumb it down' if the load pressure/temp is too high on it for the 2nd stage HX capability. Under -100c and I'm happy but if it's creeping up under load I'm looking at a mild blend. I hope not, the unloaded temp will still look good, but load is what it's all about. 300w is a challenge in a 3 stage, but 350w is going to be much more difficult.

I'm sticking to Captube. I haven't decided on exact lengths and sizing yet.

I do have a TEV I can use on stage 1, but I'm torn. TEV's are something that can get weak or go wrong over time. I'm not big on that. But in the first stage it's not that much of an issue to replace wearing parts I suppose.

I was tempted to do a CPEV 3rd stage, since I have one here and could really get a nice 'suicide screenshot' of unloaded temp, but they tend to fail like crazy when it matters most, so I doubt I'll risk it. The TEV on stage 1 would make life easy to tune, but I always get better loaded temps with a well sized captube. I really need that 1st stage to keep it cool as possible, my entire 2/3 staqe performance hinges on a solid stage 1 temperature.

My ideal targets are...

-165c unloaded evap temp 3rd stage, -145c to -150c 350w evap load temp. Definitely looking for a -150c / 300w load temp at the evap.

I won't be looking at a Control system for this to do automated Stage control unless something changes. Wiring it up and programming the PID's is a job I don't think I'm in the mood for, though I might change that later.

I'm not doing this for a buyer so I can't really justify it yet. If someone ends up jumping in later on for it, then I guess I could do that.

I'm also not looking to do a Hot Gas Bypass unless it's a request along the way. I have the prepped line and I'd have to replace it if I wanted to set up an Evap for that. An option, but I'm more interested in the thing working as a cooler than I am in complicating it's operation and construction.

So we'll see how it goes. I think that -50c with the compressor on the first stage is doable. I'm thinking around 100w of added load from each compressor, roughly 550 to 600w max. If I have to go to 402a to get it I will. I don't think so though. The 2/3 stage gasses are light by nature. Hopefully the compressor strain is minimal that way.

The 2nd stage is really relying on the 1st. At -45c under load I think that the LG can give me -100c for the 450w likely total load. I'll find out I guess. Love to see closer to the -110c mark there but I know it won't do that. Not quite.

The 3rd stage compressor is smaller in power. CC's are good but the LRA is quite low for it's size. It's a double edge there, since the lack of power could hit my actual 3rd stage performance at load, but at the same time it won't add as much compressor heatload as a higher powered one would, and if the HX can stay down there, the R50 will condense with much less pressure and hopefully keep the compressor strain down.

So that's the basic story. I'll be using my method for SLHX using brazing techniques instead of full ones. I'll be making small discharge mufflers to help with discharge pressure oscillation dampening and try to keep the oil flurry light in the sep's.

R50 is an aggressive jump. No question. -150c in 3 stages is extremely aggressive for 3 stages. To do that I need to keep it simple, volumes fairly low, and parasitic losses to a minimum.

I guess I'm looking to make the smallest, coldest, highest load 3 stage cascade that's been made in here. Not too much to ask, is it?

Some pics of the plan...






Pretty small platform. It'll be on wheels when done (it'll be about 150lbs most likely) and dimensions including panels should be around 24"x20"x12"

So I expect a month or 2 to finish it. Could be faster but I have committed to a couple of projects in between. need to remake a cooler for someone and redo a dual head gfx cooler (top case mount) for a guy at another forum. He's pretty excited and a really nice kid. He's after something that's going to cool and all that, but more about looking good. I like that. He has a Lian 8 series case and a Vapo for the bottom already, and I've got a case from a Vapo I can mod up for the top with some cool lighting so it should look sweet together, or 'Sick' as he put it

So kinda busier than I expected or want to be, but there's no deposits, no prepaid nothin' so I can just do it as the speed takes me. If it's 'too long' then so be it. I'm having fun with the stuff again and going to keep it that way.

Thanks for looking I'll update as it goes. I expect to have the first stage done relatively soon, but can't do much with the second until I have the other HX and valve.

Gray

[MaRtIe]

Interesting

that horizontal compressor is pretty funky, never seen one of those. looks like it's going to be pretty compact unlike half the multi stagers so will be interested to see how it's done

the guestimates of that load on the first stage is pretty good too if you can pull that off. 350w @ around -45 is awesome, i am guessing the 1HP compressor will play a big part in that

what diameter cap tube you gonna be going with? .042?

Martin

[Gray Mole]

Well like I said, that's a tough one to be sure about.

I think I'm looking at around 500 to 600w of required capacity on the first stage under load. If that's the case, then .042 is my most likely cap for stage 1, possibly .046.

I do like shorter captube these days alongside enhanced captube subcooling. Without it longer is a lot better.

I'm going to guess but if I do it captube, either .042 at about 6' or .046 at around 8'. Just ballpark for now, I'm going to have to do some calculations and go back to the notes I made on Gary's work.

I tried to extend his basic algorithm into larger capacitys but it's been hard to be sure if I'm right, would be nice to get a decent size first try on stage 1.

I do like to use a 5.5' to 8' length of cap, usually the shorter, on a load supporting stage.

It was only .031 cap on the smaller cascade but I reached the limit of 5.2', kind of pushing it a bit since I don't like too short.

So no set answer, though I sure will tell you when I'm sure myself

Thanks Martin

[Gray Mole]

Oh yeah, and the main reason' I'm going as high on the 1st stage as I am over the other 2 is to try to keep that 1st HX cold as I can. I'd really like to keep the second stage low since R50 is a big jump and the only way to a good result there is to have a -100c or better load result in that second HX.

That, and the the horizontal rotary gives a much lower profile and it's gonna be a really 'tall' case if I use a standard rotary as the third compressor.

I measured and 'could' fit a third one on the base, but I'd be struggling with a fan configuration that worked. I'd have to put the HX's all on the top if I did that, as well as oilseps and such. It's still a consideration but having 4cc's more on the base should mean a pretty consistently cold 1st HX.

This thing isn't going to be quiet at all though. Between the compressors being loud and the fans being fairly loud it's going to add up. I had a feeling that any kind of aggressive 3 stage would be noisy though.

Smaller high output fans are all I can squeeze in. A single larger fan would be quieter but I can't get it in without having to give up the HX lower location.

Gray