Morphing Air Conditioner into Autocascade System

So do you want the high temp (high stage?) gasses to be as close as possible to the gas temp suction side, both entering and exiting?

Means that as much heat is bring transfered to the suction gas as possible, right?

Well entering.
And yes enough refrigerant that your getting down to as cold as possible :)

So you want the highside gas temp entering the HX to be as close as possible temp wise to the suction gas exiting the HX going back to the compressor? Just making sure... I coulda worded my question better before.

I was hoping this thread didnt die.

Otha side. The entering side doesnt really matter so much.
The temperature of the high side leaving the HX should be close to the temp of the suction right before the HX (basicaly where metering device is).

Ah, I see. High side leaving HX and suction side entering HX.

Any news, mytek? Every morning I am looking forward to see progress on your new AC, but I am a little in pre-chrismas stress also :)

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Originally Posted by mytekcontrols

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.

:)

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just -80! i dont ask for too much:D, i will read and reread again all your post before starting up:)

thank u!

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Any news, mytek? Every morning I am looking forward to see progress on your new AC...

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PhilippF,
I just got done fabricating all 4 heat exchangers last weekend, and I am now assembling them into a complete stack. Probably wont get a chance to do the brazing until my Christmas vacation. So far it's looking good, although I did have a fight with the 1/2" bender on Cascade #1 (and I think the bender won :( ). Nothing that will affect operation, but there are some deep grooves on some of the bends.

I'll post pictures when the stack has been brazed :)

quintus,
-80C can be obtained with only 2 refrigerants R600 (n-Butane) and R170 (Ethane), which are hydrocarbons, so might be easier to come by (and cheaper). Will probably work with only 2 heat exchangers (auxiliary condenser and cascade condenser), and a single phase separator. Just be sure to make the phase separator fairly large, and stuff the upper end with either steel or copper wool. Having fewer stages does require that you do a better job of phase separation, otherwise too much of the high boiling component gets through to contaminate the final stage. !!!Important Note!!! When fabricating your phase separator, be sure it is constructed to handle the working pressure on the discharge side of your system (350+ psi). Also implement a high side pressure switch to limit over pressure. Either 1 5/8" or 2 1/8" OD ACR hard drawn copper tubing with copper end caps works well.

Do you know a good source Michael for refrigerants like r600? I still cant seem to find it anywhere except at insane prices. Is butane really that price?

I cant get r600, maybe but not sure r600a, the same with r170.
I can get my hands easily on: r23 r22 and r11;)(even tomorow if i want to!) say an compresor like this: T-2180GK (Debit-3,89 m3/h, Volum cil.:22,4 cmc) is enought for removing 200watt at -80 with the above refrigerants(r23 r22 and r11)?I think is a bit on the big side:D what do you think?

10x,
q

Yes, I made the same experience here in Germany. Refrigerants are quite easy to get and also (if you now the right places) cheap but hydrocarbons are "special gasses" and very expensiv. For example 8kg R23 costs me 250€ - 3,7kg R1150 350€ .

Ah thats odd. Seems the opposite here except in butanes case. I'm thinking of alternative options at the moment. I have my r11 but sorta want to save it (my precioussssss). They have those tiny few ounce bottles and such and am thinking of a r134a can tap, maybe shim it to work with butane.

http://cgi.ebay.com/ebaymotors/ws/eB...m=310005940898
Ordered.
Okay why not ;)

if it's the lighter butane thats R-600a (Iso-Butane)

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I can get my hands easily on: r23 r22 and r11

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As I mentioned earlier, R11 and R23 are a viable combination for making a -75 to -80C autocascade system.

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Do you know a good source Michael for refrigerants like r600?

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For small quantities it appears that Blazer Products has a possible solution in the highly refined n-Butane refills they offer for their Blazer tools. Here is the MSDS sheet, and it can be purchased on-line from various sources including Stan Rubenstein Assoc. Normally I wouldn't recommend using a fuel grade HC for a refrigerant, but this one might be pure enough to work OK. Ideally a refrigerant grade gas would be the better way to go, although this can get quite expensive.

I am seriously thinking about using this for my first test charge. The only problem is, I'm not sure how best to extract it from the refill cartridge. Anybody got a good idea on this?

I also came across an interesting paper by L. Maclaine-cross and E. Leonardi called Comparitive Performance of HC Refrigerants that shows the distinct advantages to using HC refrigerants, over CFC's, HCFC's, or HFC's. It appears that not only do they excel from a COP point of view, but also have better heat conductive properties, and offer lower operating pressures (hence less energy consumption). And last but not least, HC refrigerants are highly miscible in virtually all the oils being used in standard refrigeration.

Here's some pics of the 1st Phase Separator, and the brazed stack assembly.

The First Phase Sep is 1 5/8" od x 8", and has the entry tubes coming in at an angle so as to create a spin on any liquids that make up the refrigerant stream. This should help separate the liquids from the gases using centrifugal force. There are also 2 pads of the copper wool stuffed into the top to further aid the phase separation.

The 2nd and 3rd phase separators are simply bullet strainers, whose internal volume is still large compared to the internal volume of the discharge tubes that feed them, so should still do a decent job of separation, especially considering the reduced amount of liquid in the refrigerant stream at these stages.

that looks amazing.....my jaw has dropped

...wow.

That is tight in there.

...wow.

Excellent job planning that out. Im not sure if someone just could "wing it" and pack everything in there so small without serious planning. :up:

2pipes as inlet and two as gas outlet out of phasesep? why not use bigger pipes instead?

regards
Tim

Nice work mytekcontrols
I cant wait to start on a autocascade again.

so all the hxs seem to be the same length and the aux tad longer.

Thanks for the compliments, and yes it was tight and did take some planning, but not as much as one would think. I just "layered it in" (see pics below).

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2pipes as inlet and two as gas outlet out of phasesep? why not use bigger pipes instead?

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My other choices were: Option #1 one 5/16" od (discharge) inside of 1/2" od (suction), or Option #2 one 3/8" od (suction -- reversed from previous) inside 1/2" od (discharge). Option #1 would not have yielded as much outer surface area as the dual 3/16" od tubes I did use, and Option #2 would have been extremely difficult to fabricate in order to stuff the 3/8" od tubing into the 1/2" od tubing. using anything larger for the outer tubing (such as 5/8" od tubing) would have been too much volume, and resulted in too large of a heat exchanger for what I needed.

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so all the hxs seem to be the same length and the aux tad longer

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Aux and Cascade #1 are identical, and Cascade #2 and #3 are identical.

Here is the nitrogen purging set-up I used to keep everything clean inside (nitrogen cylinder and regulator not pictured). The blue hose is connected to the suction return line from the stack, and the green hose connects to the distributed lines responsible for purging the discharge circuit(s).

I first brazed the stack as shown without any discharge connections. This required moving the distributed discharge purge tubes up as I brazed from the bottom up.

After the entire stack was brazed, I then proceeded to layer in the discharge circuitry as I described previously. When doing this, I only needed to purge from the bottom, since each assembled layer would automatically complete the discharge purging circuit for me.

Wow Michael. I've got to say, I think I'm in love with that pile of copper tubing. Might have some questions for you in a bit, still sourcing parts for my own projects. Looking forward to seeing this unit complete :up:.

Awesome! Now I am really excited to see how it performs :)

Having a little hard time following the heaps of copper but would it be safe to say you have decided to use SGHX for last stage? :)