Morphing Air Conditioner into Autocascade System

[n00b 0f l337]

Sorry thinking electronegativity. Been a while since chem. Four flourines on a carbon seemed polar, but I Just realized that it would be tertral and balanced. So maybe thats why, ultimately I think its just partial pressure. When you have a liquid and a gas under pressure, some of the gas is going to enter the liquid. More so as the temperature drops, or the pressure increases.

[Unknown_road]

partial pressure is a nonsense term. it fits in the same line as a square wheel.

[n00b 0f l337]

The laws of partial pressure. When I refer to it I mean that if you have done partial pressure equations, you will often realize that its impossible to keep two things separate.
Partial pressure is the pressure that would exist if only one of the mixed substances occuppied the volume.
I guess i should simply use the term henry's law.

[mytekcontrols]

you will often realize that its impossible to keep two things separate

I think this is the essence of it, and I would have to concur.

1badhabit said... Very cool, I have a few of these in the garage that I haven't had a chance to mess with yet. This just gave me the jump start to go be creative!!

n00b 0f l337 said... I picked up a 5150btu Kenmore yesterday and am beginning basic rip down. You definitly have given me some great ideas

This is so cool! I look forward to hearing about your results

[[XC] gomeler]

Thanks for that link Michael, lots of information to be read there I understand that part about intuition through experience, eventually it sort of becomes muscle memory, you just KNOW that something is going to work or that you are damn close. Just a skill that's aqcuired through many hours of repeated labor. Thanks for all the help, might have to bug you eventually about a few gas questions later

[mytekcontrols]

Thanks for that link Michael, lots of information to be read there

Yeah I figured it would be interesting for anyone learning about autocascades, and I'm glad you found it useful.

For those that missed it: Click Here

I understand that part about intuition through experience, eventually it sort of becomes muscle memory, you just KNOW that something is going to work or that you are damn close. Just a skill that's aqcuired through many hours of repeated labor.

muscle memory... I like that

Many times I have seen where the intuitive solution is the correct one, especially when it comes from the guy or gal who has been in intimate contact with the problem.

Thanks for all the help, might have to bug you eventually about a few gas questions later

No problem. I hope I can be of help.

[esdee]

mytek, you mentioned that for lower temprature we should add 3feet of 0.031"
these 3feet should be added to the r23 or to the r22 stage, or on both stages?

[[XC] gomeler]

My head is telling me you'd want to lengthen both stages with nearly identical lengths but my gut is telling me it can't be that simple.

[n00b 0f l337]

Lengthen both, but ideally the first should be configured by its mass flow as the second should be as well. After talking with mytek, he used the same lengths just because it was conveint, which is fine but for bigger things you need to work the massflwo.

[SoddemFX]

...but ideally the first should be configured by its mass flow as the second should be as well.

He he!

[esdee]

well i did the right thing and added 3feet to both stages

[mytekcontrols]

mytek, you mentioned that for lower temprature we should add 3feet of 0.031" these 3feet should be added to the r23 or to the r22 stage, or on both stages?

It depends a lot on what temperatures you are trying to achieve, and what refrigerants are used. If you want -75 to -80C temperatures, then I would begin by only lengthening cap tube #2 (final to evap), and leave out the R-22. You will also probably want to increase the R-123 (or R-11) by 1 to 2 oz. (add 1 oz at a time, and monitor your discharge temperature. Try to keep it below +125C when the system has reached equilibrium)

The idea is that in this configuration you are attempting to have a more pure form of R-23 feeding the final cap tube (low amount of warmer boiling components in solution), hence lower temperatures when evaporated.

In my example system I was looking for very high capacity, but not extremely low temperatures (-30 to -35C). So with the R-22 being present in the charge, I was certainly seeing a considerably amount of it being dissolved into the R-23 within the cascade condenser, and probably had something approaching a 50-50 split in liquid available at the 1st and 2nd cap tubes. In an R-123 + R-23 charge you will see a shift in this split, with more liquid being available at the 1st cap tube, and less at the final. Of course we are also trying to lower the evaporating pressure through out the system and especially at the final evaporator, so we need to sacrifice heat load capacity by reducing the overall flow from the discharge to the suction. So based on all of this criteria it would make sense to decrease the flow in the final cap tube only, and see where it gets us (3 ft increase is only a rough guess).

In a traditional multi stage autocascade system, the amount of liquid refrigerant available at each separation point tends to diminish as you go higher in the the system.

You may also find that you will need more expansion volume for the R-23, since it will probably take more of it to handle any reasonable amount of load. I'm not sure what kind of static pressure the rotary compressor in the LG unit can safely handle, but this is what will ultimately determine how high your static balance pressure can be (can be determined by motor amps). Adding expansion volume (expansion tank with cap tube bleed to compressor suction) will give you more gas to work with, while still staying below the maximum static pressure for start-up.

Possible alternative non-flammable refrigerants

For R-123: R11, R-113
For R-23: R-13


I hope that helps

[n00b 0f l337]

But keeping the r22 would tend to give more capacity yes?

[mytekcontrols]

Wow quick response

But keeping the r22 would tend to give more capacity yes?

Yes, but in a single stage autocascade you will do this only with a great sacrifice in evaporator temperature. To use R-22 more efficiently, it would take at least one more cascade and phase separator, assuming your goal is -80C (or better).

[n00b 0f l337]

So lets say you add that 2nd phase separator, and another heat exchanger. R123, r22, r23 is still viable? I ask these questions both for myself and I know that everyone here is pretty out to get the best capacity at the lowest temp.

[mytekcontrols]

So lets say you add that 2nd phase separator, and another heat exchanger. R123, r22, r23 is still viable?

Yes it should be. In fact Polycold has a system called a PGC-150 that utilizes this many stages, and the same refrigerants (although it does have a subcooler and small amounts of R-14 and Argon as well). It does -120C at just over 300 watts, and utilizes a 1 1/2 HP reciprocating compressor.

But if you are just starting out with autocascade design, it is better to keep it simple, and build up from what you learn.

Edit: the PGC-150 also uses Ethane as part of its blend.

[n00b 0f l337]

I'll start with one phase sep and two heat exchangers then, then upgrade it later after of course recovering the charge.

[mytekcontrols]

Good decision

I know it'll be tough not going balls out with the first build, but in the long run I think you'll benefit far more by taking it a step at a time.

BTW here is a data sheet on the PGC-152 (same as PGC-150, just a different charge): PGC-152 Datasheet

This is a gas chiller, so each heat exchanger has a secondary circuit for feeding a nitrogen, argon, or helium gas stream through. There are inefficiencies due to the secondary heat exchange, but it has the advantage of not being easily corrupted due to leaks or poor evacuation techniques. So if it were a direct expansion system, you would probably see about 5 degrees colder across the board on all heat loads shown.

One of these would be all you need to completely cool any PC CPU combo, or for that matter 2 PC's .

These are sometimes available on Ebay for a reasonable price.

[n00b 0f l337]

Sounds good, no problem for me, I found a small gas supplier now for small quantities of r23 and r14, so I'm quite ecstatic but slower is better.

Speak of the devil...
http://cgi.ebay.com/POLYCOLD-GAS-CHI...QQcmdZViewItem

[n00b 0f l337]

Would longer heat exchangers (your current project displays 10ft of 3/16" in 3/8") or larger diameter tubing or both increase performance?

[mytekcontrols]

Would longer heat exchangers (your current project displays 10ft of 3/16" in 3/8") or larger diameter tubing or both increase performance?

Yes longer would be better, so long as you don't take it to an extreme and end up with too much pressure drop on the suction side (higher evaporator suction pressure due to pressure drop would = warmer evaporating temperature). I would think you could get away with doubling it.

Yes larger tubing could also be used to make up for pressure drop of longer exchangers.

[n00b 0f l337]

I'll post my thread now
Thanks as always for the information. I'm going to give 3/16" in 3/8" a shot as it would be very easy to bend. I've found 1/4" in 1/2" very hard to bend, the 1/2" just seems to crimp easily.

[esdee]

this thread must be the best! so much usefull data!

im keeping 2.5m cap tube for the time being as im going to give r410/r1150 a try

[Xeon th MG Pony]

I'm Necrothread this to ask you Would this temp range work for a vacuum freeze drying system?

I have a nice recip 3,100btu@45f with a built in oil cooler(SC12B 1/3hp), I want to make this system only in my case water cooled. I intend on making the system very compact. I suppose I'd be using it both as I have for a long time used alcohol to flush systems and it would be useful for that along with a freeze drying system.

All so I didn't see any lengths for the actual HX did you just use a coaxial design and use say 5meters of each?

Instead of R-11 I was thinking of R-600a, what would be the amount of the R-600a? About the same as the R-11(123)?, with the rest of the gasses as you set fourth.

The head pressure can be programed via the V46AA-1C head pressure modulated flow Valve for the water exchanger.

By the sounds of it the SC12B compressor should handle the 50Watts with no issue?

[Xeon th MG Pony]

Ok I finaly saw where you put the pipe lengths for the Hx lol!