Autocascade build to understand a closed book

[mytekcontrols]

Hi Patrick, anything new to report?

[Patrickclouds]

small update.

I'm still in the charging process.

first I've built a charging cylinder for the gases I filled as vapor.



started with the following charges and always a test for the charge:

1st charge:
R600a: 60g
R1150: 30g
R50: 23g
R740: 10g

2nd charge:
R600a: 74g
R1150: 40g
R50: 23g
R740: 10g

3rd charge:
R600a: 85g
R1150: 40g
R50: 23g
R740: 10g

4th charge:
R600a: 100g
R1150: 40g
R50: 23g
R740: 10g

example of the testrun:


5th charge:
R600a: 100g
R1150: 60g
R50: 23g
R740: 10g

on all testruns I had the same problems so they lasted max. 20 minutes
I have still not enough refrigerant in the circuit. captubes shouldn't be too restrictive. So this causes that I'm running a huge pressure ratio of over 1:14 (LP 0,5barg, HP 21 barg).
High pressure ratio and low mass flow on the LP side let the compressor stop running. That is exactly the same I wrote over the pure CO2 test that the compressor stands still and pulls 12A (230V)

the evap temperature always drops more while adding more R600a in the tests above. But the tests last only around 20 minutes so far.
with the 5th charge I could reach below -100?C evap temp.

I need more liquid refrigerant flowing through the captubes to get better compressor cooling and higher mass flow. still after the last change of the charge I'm talking now.

6th charge:
R600a: 130g
R1150: 60g
R50: 23g
R740: 10g

with this charge, much look and lot of tears in my eyes I get through the cool-down process. The compressor has discharge temps of over 120?C and was just before blocking (you hear the change of the running sound when you are close before stopping). During cool-down process when I reached -100?C evap temp it was the first time with the R600a charges that you can hear the liquid refrigerant flowing in the evap and evaporating there. I remember that I had this evaporating and liquid injection sound with the old R290, R1150, R50 charge just after starting the unit. But with that older charge I was running with much more LP. So another hint I need more gas to fill.

The testrun continues and after 60 minutes I saw -146?C on the thermometer. But because i was in a hurry I stopped test after 67 minutes at -148?C But I think there will not be no more big temperature drop because the temperature didn't change a lot at the last 20 minutes.
Temperature is not everything I prefere a stable running unit that runs in the compressor specs
So there is a lot of work to do for a better cool down.

Pics from the test run this morning:




Here is the data of the test in an Excel-sheet. Some temperatures seem really starnge.
The Aux HX HP outlet is colder then the Aux HX LP inlet. and the same withe the CC HX at minute 35.

Next step is another testrun an logging the temperatures again. (hopefully more temperatures and also pressures.)
I calculated some charge changes with refprop that should change the HP but will give me higher LP at colder temperatures.
I will start with adding some R1150 and R600a

[Patrickclouds]

I added some gas and hit the -150?C wall

also the other temperatures went down.
Cascade HX HP out gets 10K colder and AUX HX HP out gets 20K colder

[mytekcontrols]

Patrick congratulations

Truly impressive results!!!

And welcome to the -150 C club, you have certainly earned it.

When I get a chance maybe later this week, I'll study your data in more detail and feed back any thoughts I might have. But it is quite apparent to me that you truly have a handle on AutoC's, something which few can claim.

[Patrickclouds]

I ll post the excel sheet of the latest run later this day.

I used the cheapest k-type probes from china that i have found. I ordered there two times and get different probes the second time. They vary a lot around the real temp. Maybe thats why the high pressure stream is sometimes colder than suction.

[Patrickclouds]

the low pressure drop could be a freezing captube? at this point the temperatures get a bit warmeer before they continue to drop again.

[mytekcontrols]

the low pressure drop could be a freezing captube?

Unless something is out of calibration with your temperature measurements, it doesn't appear that you got cold enough to freeze any of the refrigerants in use, and if it were oil, it would probably not recover until the system had warmed up considerably, which doesn't appear to be the case.

This is more likely a re-balancing of the refrigerants, which I have seen in my tests as well. Essentially as the system cools down, a certain stage can suddenly get much colder as enough condensate is formed to make a liquid seal at the cap tube entrance, with a resultant sudden shift in temperatures, and a sudden influx of heat being carried out of the colder stages due to the increased mass flow.

This affect can be minimized by playing with the proportions of the individual refrigerants, but often times not completely eliminated.

[n00b 0f l337]

I agree with Mytek. The only thing that could do that fast is a shift in the phase separation changing the flow pattern.

I went to airgas last week about hydrocarbons and basically got told no way no how. I've got two tanks of ethylene at home but no way to get methane or isobutane and it kinda sucks!

Patrick, mind sharing your captube lengths?

[Patrickclouds]

I think it was 1,8m of 1,00mm captube. both cap tubes have the same length.

[n00b 0f l337]

Thanks Patrick.
Getting close to strapping a heat load to the Evap now?

[Patrickclouds]

no not yet. I still want to fill more low boiling components first