Morphing Air Conditioner into Autocascade System

[n00b 0f l337]

Paint?

[Unknown_road]

you said, that you recommenc a temperature difference of approximately 50°C between the refrigerants. Isn't the difference between R-600 and R-170 a bit high? According to a P/T-chart, ethane has a pressure of 27bar at 0°C
What about a mix of R-600/R-290/R-1150 or R-600/R-507a/R-1150? That would be closest to the "50°C-Rule"...
How much does Ethane in the US or in other countries than Austria cost? Here it is about 280€ for 3kg. A bit expensive

I recommend r600/r290/r170. maybe add some r1150 to make a r170/r1150 mixture but I would add another stage for it.

[[XC] gomeler]

I call the first HXC (before the 1st phase sep) an Auxiliary Condenser since it is essentially just an economizer, or what I believe some of you also call an SLHX. All the following HXC's are considered to be Cascade Condensers. Hey gomeler I read your article on autocascades... very nice

That's the term I was looking for, auxiliary condenser! Like I said, it's been a long time since I've bent my mind around this material. I'm actually in the process of revising all my articles as I feel they were written when I had a much smaller understanding of the principals behind this stuff. I still do, but it's a slighter wider understanding and actually includes some experience now

[mytekcontrols]

ou said, that you recommenc a temperature difference of approximately 50°C between the refrigerants. Isn't the difference between R-600 and R-170 a bit high?

You guys are getting good at this

Actually although I did say 50C spread is a good starting point, I also think I said something about not all designs adhere to this. Another way to put this is that if you are starting with a blank slate, with no past experience in autocascades, then keeping the spread between refrigerants to approximately 50C will give you a high likely hood of success. However it is not written in stone, and mixtures with far different spreads have been proven to work quite well (R114, R13, R-14, Argon is one of them). I was simply suggesting a hydrocarbon version of the highly successful CFC mixture that Polycold used to use. No guarantee that it will work the same, but it certainly seems likely that it can. However I also introduced the possibility of adding an additional component to help bridge the large gap between R600 and R150. Not that this will necessarily be needed, but something if needed will save the charge.

Which program do you use to make your designs?

I use DeltaCad for my diagrams.

[mike8913]

are there any gas mixture rules of advice and/or any captube flow rate procedures you would take with single stage designs?

[mytekcontrols]

are there any gas mixture rules of advice and/or any captube flow rate procedures you would take with single stage designs?

I'll have to defer this to some of the other people on this forum, who have much more experience with single stage systems.

What about a mix of R-600/R-290/R-1150 or R-600/R-507a/R-1150? That would be closest to the "50°C-Rule"...

This is referring to:

The best initial approach I can suggest (and could perhaps be considered a rule of thumb), is to try to pick refrigerants with a difference in boiling points of approximately 50C (+/- 10C). Of course an autocascade will work even if these conditions are not adhered to, but the idea is that this should give you the best initial results. The rest comes down to intuition based upon a lot of experimentation (or should we say a "gut" feeling). Some people also call it black magic.

Which was from Project Whop Post #139 it was my mistake to call this a "rule of thumb", which has been reinterpreted into a "Rule". In the future I will have to be more careful how I word things.

What I really meant to say, was that this is a good "Starting Point", but unfortunately bunged it up by adding the additional qualifier of : "and could perhaps be considered a rule of thumb". Sorry guys

Anyway moving on with my tail between my legs, what has been observed in the past, is that refrigerants with widely different boiling points can still have great success at working together in an autocascade. I talked about this earlier in Post #8 where I discuss the possibility of using only R123 and R23 to build a -80C system (a CFC version of this would be R11 and R13). Below is a schematic of how little is needed to make such a charge work (single-stage autocascade --- as simple as it gets).

[quintus]

10 seconds q' can u pls tell me fast i mean u got experience enought for this small 1: applying your last schematic, the above 1, using r11, r22 and r23 and a heat load of ~200watt, what size compressor do i need?

thx for all the good info's that u put here for us

[Unseen]

mytekcontrols thanks for posting such usefull informations and tips. You explained many things that i had in my mind with simple words. Thanks a lot.

[godmod]

What I really meant to say, was that this is a good "Starting Point", but unfortunately bunged it up by adding the additional qualifier of : "and could perhaps be considered a rule of thumb". Sorry guys

No, No. You did make it clear that it is just a rough way to go with the 50K difference. I just wanted you to tell me if you know or think if one or both of these mixed could work
Thanks for the drawing, thats exactly how i will build it. Hopefully i won't fail, but who knows, autocascading is a science

[n00b 0f l337]

Yes Mytek we really cannot thank you enough for bringing your expertise here.
I am going to order r170 I think, and attempt to find a r600 source. Hydrocarbons are nice and friendly, and flammability isnt really a concern.

[mytekcontrols]

10 seconds q' can u pls tell me fast i mean u got experience enought for this small 1: applying your last schematic, the above 1, using r11, r22 and r23 and a heat load of ~200watt, what size compressor do i need?

I'll address the part about "what size compressor do i need?" with it all depends on what temperature you require while under a 200 watt load, and of course somewhat dependent on what refrigerants you'll be working with, and how much heat exchange + pressure drop will exist. Let me just say that it gets complicated real fast, if you need a specific answer to that question, and to be quite honest, I'm not the guy with that kind of answer.

Edit: Check out the project described at the very beginning of this thread, it may help to steer you in the right direction with this.

I'm more like the guy that works on cars in his garage, in his spare time. Although he may have done it for years, he is not in the same league as the people that actually designed the engine itself. Sure he can maybe take an engine, re-build it, couple it with a transmission, drive train, perhaps build a frame, and figure out how to get it all to work fairly well together. But bottom line is, he probably does so more by feel, and a bit of luck.

However I do realize unlike some (or many) of you, I also have the luxury of having easy access to a vast array of refrigerants that can be quite expensive, and hard to get on an individual basis. So of course you are going to want to get it right the first time. So that is why with this build, and the one before it, I will show you at least 2 working versions of autocascades. This comes inclusive with everything needed to replicate my results: Compressor specs, Heat Exchanger details, and Refrigerant Charge. The first one which is of the same design as the diagram I just showed you, was designed for a specific application, and is locked into that use. So it can no longer be used by me to test alternative charges. However this second version starting out with 3 cascades, is for my own personal satisfaction, and is not being built for anything specific. Also unlike the first build, this one will be load testable.

If you choose to go off on your own, and build something different, and use a different charge. I wish you great success, and hope that whatever I have shared on this forum will have helped you in some small way. But please do understand that I am not an "expert", and have never, nor will ever claim to be so. I do this strictly for the fun of it, and also to share what I have learned with others.

When it comes to using hydrocarbons in autocascades I am the newbie on this one (other then R170). There are other people on this forum that have a much better feel for this sort of thing, and I think some have showed great results on actual working builds. LukeXE comes to mind, although I forget what refrigerants he has been using. Please tap into these other valuable minds, and don't just take my word for it.

I thank you all for the following acknowledgments (I hope I didn't leave anyone out, sorry if I did)

thx for all the good info's that u put here for us

Yes Mytek we really cannot thank you enough for bringing your expertise here.

Thanks for the drawing, thats exactly how i will build it. Hopefully i won't fail, but who knows, autocascading is a science

mytekcontrols thanks for posting such usefull informations and tips. You explained many things that i had in my mind with simple words. Thanks a lot.

Stay tuned for my progress on my AC2 Project

[jinu117]

You are being too modest Michael
The experience and gathered set of data can't be denied.
As you know, lot of this heat flux and flow, etc are being calculated based on experimental data (unfortunately, most of equations available are close but no cigar as complexity of behavior under gradient temperature, heat flux, and surface tensions are not something that has been fully analyzed yet).
This comes as even more of complication I bet when it comes to auto-cascade. There might be equations that people use that are pretty close but I bet last 20% of it comes from years of experience. (in fact, neural network AI is quite often used in industry it seems in field of cryogenic... which is nothing more than emulating what human mind is capable of).
When such new variables comes in as different gases, etc... of course, it might be some larger amount of change until you get it under control in your mind :P
We really do appreciate your contribution even if there are some things overlooked as it is still TONS better than what is available to use easily (nope... after reading 5th cryogenic book... lol... you still have a lot of imperical data that is useful to us than these books do... haha)
Many thanks to people like you and Detroit AC who are in field and spend your valuable time to enrich the community again.

[Polizei]

To me, it seems that Mytek is valuable because hes got a lot of first hand experience with exotic refrigerants and knows the in's and out's of cryogenics in a way that users here dont. Not saying the regular phasers here dont know anything, Mytek just has a lot of first hand knowledge that us here cant get from books.

If only Mytek had a "search" function so he didnt get bombarded by questions.

I love watching projects like these and reading posts about theory and planning of refrigeration like this... I learn a lot more than just reading threads about "Why doesnt my MachII like my QX6700" or "My Vapo is broken." Its almost a privilege to stand back and watch great minds converse like this.

to you guys.

Many thanks to people like you and Detroit AC who are in field and spend your valuable time to enrich the community again.

[n00b 0f l337]

On a slightly off topic note, is it just me or butane nearly impossible to get here at a decent price. In UK it seems it'll cost you $30 or so for a big cylinder, like we do in the USA with propane, but butane here I've gotten quotes for $300+ for 99% purity n-butane.

[[XC] gomeler]

Aren't there cylinders of butane used for camper stoves or are they a dirty blend of various hydrocarbons? Not talking about the green camper fuel cylinders as those are nearly pure propane.

[PhilippF]

Here in Europe Butane is quite common for camping stoves, but its a wild mix of n-butane, iso-butane, propane and some unidentified hydrocarbons, so I would not recommend using it. Also lighter gas (for lighters, you know what I mean) is mostly butane, but I wouldnt recommend it either.

[tim-]

well.. I can get 100% pure propane, n-butane, iso-butane from gas supplier here ... since it's used in different kind of heaters.

[n00b 0f l337]

Yeah well I cant seem to find that

[mytekcontrols]

You are being too modest Michael
The experience and gathered set of data can't be denied.

OK perhaps I am, but It's always made me a bit uncomfortable when too much is riding on what I say. And although within this forum I may sound quite confident in my answers, some times I am shooting from the hip, maybe saying something that I hadn't let my mind fully wrap around around yet. Or another way to put it, would be to say I am thinking out loud.

...in fact, neural network AI is quite often used in industry it seems in field of cryogenic... which is nothing more than emulating what human mind is capable of

Have you guys put one of these together yet, and tapped it into these forums? I think it would be a great idea, and while you are at it, add Polizei's search function request to it

By the way, thanks jinu and Polizei for your appreciative comments as well (it means a lot to me)

Back to the AC2 Project:
I will be updating the piping diagram soon, to include a combination buffer/expansion aspect which I believe will be needed to have enough gas present to realize the full load rating of the unit, while at the same time accommodate the compressor's start-up requirements.

I will also be adding in all 13 temperature points I described on an earlier post, so everybody can have a much better idea of the locations. This will be very important when I get into the testing stage, since I will be sharing test data that will reference these same points.

Hopefully the first tests will commence in late January of 2008

[Polizei]

13 temperature points? Does that mean youre going to be measuring gas temps throughout the entire system?

Excellent idea there... tons of info awaits!

[n00b 0f l337]

More importantly he's now given me enough insight as to how to charge. Charge to get as little a delta at outputs of an HX.

[Polizei]

Delta between what?

[n00b 0f l337]

Output high side of HX and input temp.

[Polizei]

Im confused... low stage or high stage?

I have too much to learn.

[mytekcontrols]

More importantly he's now given me enough insight as to how to charge. Charge to get as little a delta at outputs of an HX.

Delta between what?

Im confused... low stage or high stage?

Polizei check out Post #165 for more info on what Nol is talking about.

13 temperature points? Does that mean youre going to be measuring gas temps throughout the entire system?

Excellent idea there... tons of info awaits!

Yes to all your questions. It will give us some very valuable data that up until now, has been sadly missing with the autocascade projects.