Autocascade build to understand a closed book

[Patrickclouds]

I've read a lot on mixed refrigerant cylce and decided to get my own experience with it. First I start building a Linde-Hampson-Cycle with only one Refrigerant. Bit I didn't finish it. One refrigerant because I didn't want to waste expensive gases for no results
After I saw the load test result of myteks CryoBug I thought I can give it a chance.
So I thought about different designs but end up with myteks CryoBug because less phase sep reduces cool-down time and decrease high pressure. I installed a buffer volume to get more room for experimentation.

Final charge should be R600a, R1150, R50, R740

The specs:
compressor: 21ccm R407C Samsung rotary compressor
air condenser: ECO 1,2kW, 230mm fan
cap tube: 1,0mm 1,5m each phase sep and subcooler HX
HX stack 12x1mm outer , 6x1mm inner
aux HX: 5m
cascade HX: 6m
subcooler HX: 3m
hotgas HX: 10x1mm/6x1mm
phase sep / oil sep: 35x1mm 25cm
buffer volume: 8l Klimal

Picture of the Design:




I charged the unit with R290 and R1150 for the first testrun, 100g each.
The temps and pressures I get:



First I start with filling the 100g R1150 and then I start the unit while filling 100g R290. So I should have the whole expansion tank filled with only R1150 that is not in the cylce so far. I think after a restart the gases will be better mixed and I hope for some degres colder.

The question is which gas should i fill now? The Aux HX and suction line is much too warm and evap could get a bit colder with that charge


Now here are some pictures for a better understanding:

Evap design with cap in cap:









Phase sep and oil sep:



HX stack after bending around a 10l refrigerant bottle:



HX stack while brazing:







HX housing, manometers, mgv and pressure switches:





Finished unit:

[n00b 0f l337]

I approve, I approve, I approve.
And incredibly well done as well!

I don't expect r290/r1150 to work on it's own though. I think the main thing we've learned is you need that lower pressure refrigerant in there. Mytek worked with r600a/r1150 I believe as well. But r600a/r290/r1150 should work.

[Patrickclouds]

second start of the charge above gives me -69,4?C Evap Temperature.

Then I added approx. 10g R50 and the temperatures drop

I could reach -111,4?C Evap temp. So far so good, but I think I will get trubble with the high pressure starting the unit the next time. So time to start with R600, R1150 and R50.
And I will use a charging cylinder because my wight scale is nearly useless

Photo from the first test with 100g R290 and 100g R1150:



Photo from the second test with 100g R290, 100g R1150 and 10g R50:





Picture from logging the temperatures of the old charge and while adding the R50:



And a comparison of both charges:

[runmc]

Beautiful job. I love your work but auto cascade looks soo complicated for me. I bet you have $2000 in material already invested.

[Patrickclouds]

250€ for the unit itself. without gases so far

[n00b 0f l337]

With the expansion tank and your blow off the startup pressures shouldn't be bad.
You've done a beautiful job. One of the first we've seen for our kind of systems.
Might want to get a real evap on there though before you load her up.

[sdumper]

German engineering at its finest!

Very well done!! My hats off to you!

[mytekcontrols]

Patrick it is a thing of beauty

Glad to see others picking up the AutoC designs and running with it. Great idea on adding the liquid line HX to heat up the phase separator gas stream when buffering, and also smart to add a filter dryer between the tank and the buffer solenoid valve to prevent loose junk in the tank from fouling the valve. looks to me like you are on the right path.

[n00b 0f l337]

Any recommendations on starting charge? I think that's where Patrick is at.

[mytekcontrols]

Any recommendations on starting charge? I think that's where Patrick is at.

I can't give away all my secrets, but Patrick had it right when he said R600a (isobutane), R1150 (ethylene), R50 (methane), R740 (argon). I would start with 40 grams of R600a, and then go heavy on the R1150, with equal parts of R50 and R740 at about half the amount of R1150. That's all I'm willing to say for the moment. And of course start with less of everything (keep the total static BP below 150 psig, so you can add a gas at a time to see the effect).

[n00b 0f l337]

That little r600a? Wow I was off.
I know it's a lot to ask, but thank you Michael. Just that kinda hint is important.

[Patrickclouds]

thanks for your advices Michael.
I calculated some charges with lots of R600a. Most around 40% mass of the total charge.
Is it a correct interpretation of your words that a large amount of R1150 will lower the temperatures on the AUX HX a lot to the right way?

The R50 in the charge filled at the moment caused an incredible fast decrease of evap temperatures. But it has a very low density so I need a lot of R50 in the cycle.

I continue with some testing and measuring with the actual charge. I'll still place more temp probes on the HX stack. It would be nice to record more than only 4 probes at a time but I think it s a bit overkill to buy two more thermometers only for the autocascade project

very exciting journey so far

[Charles Wirth]

Very nice, thanks for sharing.

[mytekcontrols]

Looks like we lost a couple of posts

[Patrickclouds]

I still have your comments on my smartphone:

mytek:

thanks for your advices Michael.
I calculated some charges with lots of R600a. Most around 40% mass of the total charge.
Is it a correct interpretation of your words that a large amount of R1150 will lower the temperatures on the AUX HX a lot to the right way?

The R50 in the charge filled at the moment caused an incredible fast decrease of evap temperatures. But it has a very low density so I need a lot of R50 in the cycle.

I continue with some testing and measuring with the actual charge. I'll still place more temp probes on the HX stack. It would be nice to record more than only 4 probes at a time but I think it s a bit overkill to buy two more thermometers only for the autocascade project

very exciting journey so far

Actually it'll probably take more R600a, depending on the size of your compressor. What's the displacement? Figure on 35-40grams for 5ccm displacement (rotary compressors), and just increase this as you increase your compressor size.

The R1150 along with the R600a will be doing the bulk of your cooling, and yes the most temperature drop will be in the aux condenser. Also having more temperature data across the stack viewable at one time can be extremely valuable when tuning the charge, and for developing a better feel for what refrigerants are doing.

You really won't need all that much R50 or R740 for that matter. The R50 just serves to create an R14 like refrigerant out of the R1150. Using too much can be determental and will simply push up your discharge pressure needlessly. Same thing for the R740, small amount is best. With R740 I think what you are really seeing is the partial pressure effect making the evaporator pressure appear lower than it actually is, thus allowing a colder evaporation temperatrure to be achieved. Lastly you might not need R740 at all if your target temperature is around -120 to -130?C. But if you don't plan on using it, make up the difference with R50.

Good luck, and that's all can really share at this time. The rest can be learned better by experimenting and developing your own intuitive insights.

NOL:
He's going a bit bigger than 5cc... He's using a 21ccm.
Bigger is the better right?

[mytekcontrols]

I still have your comments on my smartphone:

mytek:

Actually it'll probably take more R600a, depending on the size of your compressor. What's the displacement? Figure on 35-40grams for 5ccm displacement (rotary compressors), and just increase this as you increase your compressor size.

The R1150 along with the R600a will be doing the bulk of your cooling, and yes the most temperature drop will be in the aux condenser. Also having more temperature data across the stack viewable at one time can be extremely valuable when tuning the charge, and for developing a better feel for what refrigerants are doing.

You really won't need all that much R50 or R740 for that matter. The R50 just serves to create an R14 like refrigerant out of the R1150. Using too much can be determental and will simply push up your discharge pressure needlessly. Same thing for the R740, small amount is best. With R740 I think what you are really seeing is the partial pressure effect making the evaporator pressure appear lower than it actually is, thus allowing a colder evaporation temperatrure to be achieved. Lastly you might not need R740 at all if your target temperature is around -120 to -130?C. But if you don't plan on using it, make up the difference with R50.

Good luck, and that's all can really share at this time. The rest can be learned better by experimenting and developing your own intuitive insights.

NOL:
He's going a bit bigger than 5cc... He's using a 21ccm.
Bigger is the better right?

I'm glad you still had a copy of that

A 21 CC rotary compressor will probably need approximately 150 grams of R600a. This is just an intuitive guess, but it should get you close. Let me know if this works for you. Of course so as not to waste refrigerant, you can start with a lower amount initially and add in more later.

Once again, good luck with your experiments

[Unseen]

Beautiful work! I never had the chance to build a proper autocascade myself.
I really enjoy your builds guys. Thanks

[Don_Dan]

Great work, Patrickclouds!

Looks like we lost a couple of posts

See here.

[Kevin Hotton]

Nice Autocascade, Patrickclouds. How is testing/tuning going? Looking forward to an update.

Kevin

[mytekcontrols]

BUMP BUMP

How's it going Patrick? Any more test results?

Here's a little more inspiration for you



This is my latest mini AutoC running on R600a, R1150, R50, and Argon. There is an odd thing about this, and that is I'm running this on my recovery pump which you can see in the background. Yes that's right, it's my compressor for this test.

I blew up my first little Aspen compressor on the very first test run! It was like throwing $450 in the trash can. Anyway I didn't want to do that again, so I opted to use my recovery pump (which is more robust) to find out what was happening. Anyway suffice it to say my cap tubes were grossly undersized, and the discharge pressure built up so fast, that it blew up the Aspen before I or the controller could shut it down. For the complete article, check out my blog.

I'm hoping that you are having better luck.

[Patrickclouds]

sorry to hear the bad news. keep fighting

undersized means they were too long or too restrictive. Do you had a too large compression ratio? Or was it of weak cooling because of low mass flow and winding blew up?
Do you remember some numbers? especially suction and discharge pressure, current and discharge temperature?
Can you expulse that you had no oil return problems during the test moment when it blew up?

I had less time to do anything on my autocascade. I hope to finde some time this weekend to do some more tests with the actual charge and fiber glass insulation. I have to remove the fiber glass insulation again and push it bette rin all holes around the hx stack. This time I make it outside in the garden

[mytekcontrols]

undersized means they were too long or too restrictive. Do you had a too large compression ratio? Or was it of weak cooling because of low mass flow and winding blew up?
Do you remember some numbers? especially suction and discharge pressure, current and discharge temperature?
Can you expulse that you had no oil return problems during the test moment when it blew up?

Hi Patrick,

The cap tubes were way too long (very restrictive).

Compression ratio was way high.

Cooling was not an issue, since the compressor wasn't running very long before it ceased to function.

I wasn't monitoring current or discharge temperature, and it was difficult to see the true peak discharge pressure since I was monitoring with a pressure transducer (no gauge) with an averaging algorithm. However with that said it looked like it went beyond 400 psi, and the compressor was only rated for 350. The suction dropped into a vacuum.

I pulled the compressor and dumped out the oil, measured it, and it was hardly lower then when it was filled. So oil return was not an issue during the short run.

The pressures were much better after I shortened the cap tubes; being 32/250 psi after pulling down to -131 C (this was with the recovery pump being used as the compressor).

[Patrickclouds]

I didn't write that i had also very strange problems on my first testrun.

I used pure CO2 (R744) to see that all captubes are open and I wanted to see if the unit can liquify a gas with only Joule Thomson expansion.
The compressor becomes very hot and after a time of runnig it changes the motor sound. it seemed for me that the motor has a resistance he has to work against. motor runs slower and slower until it stands still. during that you can see the rising motor current.

here is a video of the behavior with CO2: https://www.youtube.com/watch?v=lCukmqvPT7o

[Patrickclouds]

meassurement with the old charge:

[sdumper]

Patrick curious why you chose Methane instead of r14 was it a cost thing?
Anyway, thanks for creating this thread. Im still having a tough time wrapping my head around (understanding) the whole gas/liquid flow but your thread is helping me understand better.