Autocascade questions...

[Derek]

I'm acquiring parts for an autocascade, I've built the heat exchanger in berkut's style with a corrugated copper pipe as the middle layer and I've got everything necessary to get this set up except the phase separator.

First off, I have both propane and r22 for high stage gas and co2 for the low stage gas. I have a feeling that since you need a good amount of capacity for first stage that r22 would be the better choice, but since I'm using mineral oil I've also been told that the propane is going to carry the oil much better than with r22. Which gas would be preferable?

Secondly, as I stated I still need to make a phase separator. I was going to make one out of 2" copper pipe but the shortest/cheapest I can find in my area is 10' piece and it's like $80. So I want to go instead with a short, fat camper stove style propane bottle (green coleman).

If possible I'd like to put some copper wool in it but how easily could I cut the bottle/braze it back together and keep structural integrity?

Also there are 2 schraeder-like valves on the canister. One at the neck of the bottle and one just to the side towards the top. I know I need to drill out the one inside the neck of the bottle and put the co2 line there, but what should I do with the other valve? I was thinking of running the high side co2+propane through it, just look at the picture attached for what I mean.

Finally, I've built at least 4 single stages (best one running @ -60C on propane) and having thoroughly researched autocascades for the last several months I've got a pretty good idea as to what I'm doing here -- so there's no reason to get excited about me killing myself.

[Xeon th MG Pony]

90% R-22 & 10% R-290 for first stage by weight, probably don't even need that much R-290.

[Derek]

When charging by weight I am assuming that I put the refrigerant on a scale and use the difference before/after the charge as the amount I put in; or is this oversimplifying it?

[wdrzal]

Welcome to XS:welcome: Since your new here's some question to answer.

Do you know what the High side pressure will be??????????????thats where separation has to happen.

Do you know the pressure a propane bottle will hold ????????????? large diameter tubing???? how to correctly fabricate a pressure vessel?????

what and how are you going to control pressure??? How you can be sure your build is safe. consider chemical energy(flamability),pressure,and of course you can measure amps so you don't overload compressor.

IMO no one has built a auto cascade that truly auto-cascades other than a 20,000.00 dollar professionally built one.

A auto cascade should preform the same a a duel or triple standard cascade.IMO

Have you done any refrigeration work at all,other projects????

post some pics of previous builds and let us in on what you have built in HVAC/R/E

Keep in mind safety in #1

ps minus 60 C and is that loaded or unloaded ????un-loaded temps don't mean anything, love to see some of your builds ,post some pictures

[gosmeyer]

Welcome!

[Derek]

Yea I've been around for a while just lurking... Registered in 2004. I'm Strida from OCForums.com

Anyways, I don't have a digital camera (well the g/f does but I don't use it) and have never really had the need to take any pictures of my builds since I build them for myself -- not for people to look at (meh, I'm a lurker at heart).

What I can tell you though is the -60C was with the cpu (Xeon 3060 @ 2.4ghz 1.3vcore) idle. When the SS was loaded evap temps are about -48C to -50C. My cases have always been ghetto (my most recent build is in the the bottom of a custom MDF case).

While I'm not too enthusiastic about proving myself by answering your questions, I realize that you're making a point that I need to know what I am doing and not just do what I am told. For that reason I've got no problem answering them.

I'm estimating high side pressure will be around 200 psi, and yes, I realize that is where separation takes place after the condensor.

No I am not familiar with the pressure a propane bottle will hold, and you've got me here because I simply am doing what I have seen other do without fully understanding it. What I have done though, is I did look through the MSDS for different propane bottles though never found any compelling information. So I just decided I would do as others and use the propane bottles.

No I do not know how to fabricate a pressure vessel, originally I was going to use a 2" diameter copper tube with copper end pipes but as I explained -- too expensive.

The diameter of the tubing from compressor to condensor and condensor to phase separator will be 3/8". From the phase separator to the heat exchanger I was planning on 1/4" (honestly b/c it's cheaper and I'm out of 3/8" and have a good 10' of 1/4" left).

For pressure cutoff I was going to use something like this (http://www.under-the-ice.com/product_info.php?cPath=37&products_id=86) but probably from my local refrigeration shop so I don't have to pay shipping.

No I've not done other refrigeration work other than building different single stages for myself.

Well I think that covers your questions... What's my score?

Wow, just realized I sounded like an ass.. Didn't really mean to come across this way..

[Derek]

Here's the MSDS of the propane bottle.

http://www.coleman.com/coleman/msds/propane.pdf

[Xeon th MG Pony]

In such an application I would feel nervous as it is being subjected to on off stress far more than any application and the type of steel it is made of will not take kindly to that.

Use it as a tank, and get your self a cheap Temprite oil sep.

FYI you can use difference or you can just zero the scale ;)

BTW: The MS-DS is for the propane not the bottle, a friend who works with a propane company says they can with stand around 300 to 400 PSI be for the relief valve fires off. I would never suggest to even attempt to push even near thoughs limits.

[Derek]

Fair enough... With the oil separator, I wouldn't have to make any modifications to it for it to be used as a phase separator?

One question that wdrzal raised for me was the performance of autocascades. I have always wondered why autocascades perform so much worse than a standard cascade? I can really only think of 2 things, 2 compressors is better than one, and poor phase separation. Obviously there's a lot more than just these two things affecting performance, but honestly is it just the fact that a 1 hp compressor autocascaded can't do what 2 cascade compressors can causing poor (in comparison to a traditional cascade) performance or what?

[wdrzal]

that msds is not on propane bottles just propane. I used to have a pic of a home separator made of copper tube and flat tops and bottoms, its was seconds or a few psi away from catastrophic failure. I 'm hopping there is a pic of it on my PC in the closet as it disappeared from the archives.

I don't grade people only try to make them realize how much they don't know, It's what you don't know that injures or kills you.There is a VERY LONG LEARNING CURVE. in refrigeration,your not only acting as a tech, but a designing engineer. It your responsibility it's built safe.

how about a schedule 40 steel pipe with threaded end caps, you can drill and thread for pipe tapered fittings or if you have a mig welder weld in some nipples. or a arc welder, you can by rounded domes to fit pipe diameter if you don't want threads ,you need to be a good welder. on job site certified welders are required.

Never trust your life or family's ,because someone else did it as you don't know tank thickness ,surface area,more surface area =stronger tank must be. plus they probably never checked their calculations. A propane tank on the shelf @ 120psi is far fro what high side pressures can be,of course a lot depends on gas and temperature. know how to Read P/T charts and sub cooling and super heat?I just don't what to see people over reach and get hurt or killed,I can point you in the right direction to find a book or material you can trust. A 12 word question may take a dozen pages ++++ to answer ,most don't have that kind of time . so research of every part of your build is up to you as YOU are responsible if a accident happens or a home burns down.

just a blunt bit of realism;) Good luck and don't over step your limits.research is how you learn, not copying others who may or may not know what they are doing.

buy or get a good book from the library for starts,forums and the net are NOT edited for accuracy.They are a great place to ask questions and someone will point you in the right way. Kepps your thread out of pm where thet can't be watched over or if bad advice is given it can't be challenged. public threads and everyone learns .even from failures,just so they arehopefully minor.

hope you have a succesfull build:yepp: :) :) :)

[p8ntslinger676]

IMO no one has built a auto cascade that truly auto-cascades other than a 20,000.00 dollar professionally built one.

I bet Reggie has built one:)

[Derek]

Thanks for the advice wdrzal, I take it to heart. Really the reason I came here to ask about the phase separator was because I wasn't really comfortable making one out of the propane bottle but I'm glad I've been pointed in the right direction.

I don't weld and the only person I know who welds well owns a business and is always busy so I think I'll wait for a cheap oil separator to show up on ebay and jump on it.

And yes, I do know how to read p/t charts. After all, as you mentioned p/t charts, subcooling, and superheat are really the keys to tuning a unit and unlocking its potential (as well as keeping you safe of course).

[wdrzal]

I bet Reggie has built one:)

he did some attempts ,but none that I remember that he was satisfied with himself. But thats my poor memory and I'm sure not speaking for chilly. All his builds are in the archives, some of those autocascade drawings posted in the stickies are just a few possibly therioies of his. It's stated they or some were not tested so stert your seach there. past knowdledge thats been forgotten about might help all. happy searching:) :) :)

[zabomb4163]

IMO no one has built a auto cascade that truly auto-cascades other than a 20,000.00 dollar professionally built one.



cryotek builds -150C cascades that hold 1,000+ watt loads for a living. Your comment is kind of odd reasoning. If one has the ability to build well performing auto cascades then they will most likely sell them thus making them "professionals". One other member on these forums also builds super autocascades for a living.

[wdrzal]

When charging by weight I am assuming that I put the refrigerant on a scale and use the difference before/after the charge as the amount I put in; or is this oversimplifying it?

A very accurite scale so you can reproduce the mix.

Xeon I,m sure will explain specfic gravity and conversion,since all refrgerants don't weight he same,some are heavier than water,some lighter.

[wdrzal]

cryotek builds -150C cascades that hold 1,000+ watt loads for a living. Your comment is kind of odd reasoning. If one has the ability to build well performing auto cascades then they will most likely sell them thus making them "professionals". One other member on these forums also builds super autocascades for a living.

All I,m saying,believe what you want,I know the true story, did you ever see someone build a polycold or similar auto that held similar loads and temps on XS ,if so show me.


Zabomb If I was you, change your avatar or leave blank if removed is was done for a reason, XS is not a democracy, its privately owned and we are all here @ the pleasure of the owners. I would Not aggravate them. Thats just some common sense advice.

[wdrzal]

Fair enough... With the oil separator, I wouldn't have to make any modifications to it for it to be used as a phase separator?

One question that wdrzal raised for me was the performance of autocascades. I have always wondered why autocascades perform so much worse than a standard cascade? I can really only think of 2 things, 2 compressors is better than one, and poor phase separation. Obviously there's a lot more than just these two things affecting performance, but honestly is it just the fact that a 1 hp compressor autocascaded can't do what 2 cascade compressors can causing poor (in comparison to a traditional cascade) performance or what?

Yor reasong is a little off every compressor added in a cloesed thermodynamic cycle you major heat sources are

1;LOAD heat being moved
2;heat of compression, this is the wattage of the compressor that is tured into work and heat,2 compressors double the heat of compression

then you have your normal heat gains,actually 1 compressor should have the advantage. mixing gases is way to complex unless you have chemical engineering degrees along with thermodynamic ones.

Most here if the by accident hit the super mix by accident, they counld never reproduce it because they don't have the equiptment to mix gases. And quantify the mixture

Stay with pure refrigerants so you can read a P/T chart...............home brewed mixes don't have one.

[Blaster]

IMO no one has built a auto cascade that truly auto-cascades other than a 20,000.00 dollar professionally built one.



http://www.xtremesystems.org/forums/showthread.php?t=131915

so this unit is not autocascading?? lol

[Xeon th MG Pony]

No conversions needed when going by mass weight. you just have to log very carefuly every game/once you add and when you got it tuned idealy add them all up seperately and remake the mix in a bottle & test it for consistancy.

If we where talking about recovery then yes conversions are needed to calculate how much the bottle will hold.

All ways remember it isn't a race, take your time and add gas nice and slow and let the system balance out.

and tuning to perfection takes time, took three days for me to get a comercial fridge to hold .5C and it turns on 3.5c :) Neat to see all the thermometers read zero with out the water freezing!

[zabomb4163]

Zabomb If I was you, change your avatar or leave blank if removed is was done for a reason, XS is not a democracy, its privately owned and we are all here @ the pleasure of the owners. I would Not aggravate them. Thats just some common sense advice.

my avatar was replaced by staff with the one you see currently. I believe i am not the only remember who left the replacement as a reminder.

[n00b 0f l337]

Sure then Wdrzal, why don't you define what a truly autocascading system would be.

[ak_47_boy]

I guess a true auto cascade would use many types of gases that are scientifically formulated and mixed to eliminate separation?

Derek, the seams on those small propane tanks suck. They will tear open at auto cascade operating pressures. Especially during testing/experimenting, get the wrong mix and it will shoot to 700psi(boom).
I believe those little oxygen tanks are at a lot higher pressure aka stronger. You could also use a paint ball co2 bottle, they come in many sizes and can handle 1000psi easy.

[Derek]

Thanks again for all of the advice everyone. Anyone else verify the information about the oxygen tanks/co2 tanks? I do have an empty oxygen tank I could use -- looks just like the mapp gas tanks except no second valve. The co2 tanks are cheap as well, so I'll look into them.

I've read that the seams will melt when you braze the bottles, I suppose this is one of the main reasons they fail?

Also guys, I've read a lot of nasty threads and they seem more common with autocascade threads. I would prefer it if this thread doesn't turn into what so many others have.

[Sneil]

Just chose not to read "specific" people's threads from now on and you may actually get some constructive encouraging responses that will give you the information you need, not just annoying babble.

[p8ntslinger676]

i got an extra pure energy nitro tank sitting around from an old gun setup, its rated to 3000psi 48 cubic inch and is all aluminum if you want it, ill give it away for cheap. you'd probably want to get it re hydro'ed once your done modding it to make sure it will still work for you. it has a 800psi reg on it, it hasnt been used in years now that i have my 4500psi fiber wrapped tank.

here is what it looks like:

http://www.paintballadrenaline.com/v3/files/detailed/d_292.jpg

[Derek]

Eeek, brazing aluminum is doable but I'd definitely rather avoid it. You know if any of the paint ball bottles are steel?

edit - Actually, now that I think about it, can you braze copper to aluminum? You'd melt the aluminum before the copper was even close to being hot enough.

[p8ntslinger676]

no, but i found a steel co2 tank that you could use, its a 20oz

http://www.trademygun.com/Shop/Control/Product/fp/SFV/32008/vpid/2903294/vpcsid/0/rid/123841

and here is a 9oz if you want something smaller:

http://www.punisherspb.com/ProductInfo.aspx?productid=9-OZ-CHROME-MOLY-CO2-TANK&affid=1


those were the few i could find since most of the new tanks are all made of aluminum or composite wraps.

[Derek]

I'm honestly not sure if 20oz would be big enough... I'm just imagining a soda bottle...

Did some more searching on ebay and I guess that most co2 tanks are aluminum.

[p8ntslinger676]

I'm honestly not sure if 20oz would be big enough... I'm just imagining a soda bottle...

Did some more searching on ebay and I guess that most co2 tanks are aluminum.

do you want a pic of one? ill take one real quick to show you compared to a 680i mobo.

[Derek]

I'm pretty sure I've got a feel for how big it is (physically), I just don't know if it has enough size to slow down the high side enough that the r22/propane separates from the co2 well.

Just so everyone knows, I'm working in a space that is app. 10 1/2" high, so any bottles taller than, say 9" will be too tall for me.

[p8ntslinger676]

here you go, i set it next to a 680i mobo and a 12oz soda can, hope this helps some:D

http://img390.imageshack.us/img390/5756/p1200002ug8.jpg

[Xeon th MG Pony]

a soda can is more then big enough for a system, albeit structural integrity would bar even the thought of it, but the size is right, now just find a pressure vessel that size and your set!

[[486]]

cale ;)

a friend who works with a propane company says they can with stand around 300 to 400 PSI be for the relief valve fires off.

i said that a week or two ago and was just saying what i learned from really old posts here.

good luck on your auto! [mine is sitting without an evap, its too easy for me to lose interest in something near completion:rolleyes: ]

[wdrzal]

whats wrong with a 5# or 10# co2 bottle like used mostly for beer kegs at parties.

[Derek]

I've only got about 10"-11" of space to work with (height wise).

[wdrzal]

The bottle is to charge with,theirs enough internal capacity for the refrigerant.

[Derek]

Well I have a bunch of 1" tubing that I have no use for so I mocked this up for a phase separator using it. I don't feel comfortable just using 1" b/c it seems to small to me (velocity would be too high) -- which is the reason it would go through 2 tubes.

Just imagine each tube about 6-8" tall, and 1" diameter tube. Also it will be filled with copper wool and I will use endcaps for ends of both tubes.

Honestly btw, I just love the whole DIY element which is why I'm moving away from using an oil separator or CO2 bottle as phase separator. Also, I have the materials to make this and it can be done fairly compact. Also, just as a pet peeve/neatness factor, I like all of the tubes coming from the top and bottom instead of drilling through the sides.

[p8ntslinger676]

interesting idea, i like it:D

[n00b 0f l337]

So basically your aiming at a double separator. The only problem that exists there is when you trap liquid in the first.

Give it a shot :)

[Derek]

The idea came to be when I read someone's comment on how the tempright oil filters used baffles to separate the stages.

The liquid shouldn't get trapped in the first separator b/c:
A) The feed line in the first separator should only be about 1/4" from the bottom of the separator.
B) Even though the liquid has to travel UP before being emptied out into the second separator, pressure should move it through without any liquid getting backed up. Just like right after your standard condensor on a SS the liquid line exits the condensor, travels up (so that there's room for the filter/drier to be pointed down) and then back down as it goes through the filter. The liquid doesn't fill up the condensor (if properly charged) even though it is being pushed to a higher point than the exit of the condensor b/c the compressor is pushing it along.

Edit -- I'd also like to note that I really have no idea how much liquid will be in the phase separator, the pic is just a sketch to illustrate the idea... I'm assuming that there'd actually be more liquid in there than what I have drawn (at least in the second separator).

[[XC] 2long4u]

Eeek, brazing aluminum is doable but I'd definitely rather avoid it. You know if any of the paint ball bottles are steel?

edit - Actually, now that I think about it, can you braze copper to aluminum? You'd melt the aluminum before the copper was even close to being hot enough.

You can braze copper to aluminium. I think its a aluminium rod.
http://youtube.com/watch?v=62t61RZ37Bo :up:

[n00b 0f l337]

Why not stack one tube setup above the other, connect the bottom of the top one thru the bottom one to the bottom of the bottom one. So liquid drops down a 3/8 or 1/2" tube to the bottom one, and both separate out the top then merge the two gas outputs.

[[XC] 2long4u]

Remember height is a factor. To get liquid to flow out the first chamber you may need to put a slight restriction in the upper transfer tube. :up: The paint ball co2 bottles I've see are very heavy so I think they would be steel.

[n00b 0f l337]

Height helps, but inner design can make up for that. I'm going to be testing some Temprite 304a's as phase seps, I think they should work very well.

[SoddemFX]

In the gas velocity reducing separators i think wide would be the main thing, so wider would be good, height lesser.

Be carefull with wide home made separators, the high pressure acting on the larger surface area puts a lot more stress on your joins and materials.

Using centrifugal (god help me Adam, if you mention centrifugal not being a force i'll hunt you down and bludgeon you to death with a wooden spoon :D ) effect to separate the dense liquid from the much less dense gas would be great, i think the Temprites are centrifugal. In the home made separators having an off centre entry would create a spinning column to do this - one of the professional auto cascade guys said a while back.

Tom

//Brasing aluminium to copper?! How the hell does that work? :confused:

[n00b 0f l337]

Aluminum rods and a temperature probe on the aluminum 6" from the joint makes it possible with mapp torch!
Hahah won't bust ya on centrifigul. I wonder why causing that would help separation though? Maybe just like in a centrifuge, high velocity rotation causing a density separation. Hm... Tempting to try something like what your talking about, an off center input. I think I'll stick with the 24 temprite 304a I got.

[SoddemFX]

Hmmm... thanks but i'll stay clear of it, sounds way too dodgy :)

Yes, in a centrifuge the spinning causes the more dense things to be forced against the outer edges, the less dense things stay in the middle. In a phase sep you have liquid and gas, density is probably a few orders of magnitude different so separation will be huge, like steel ball bearings in water. I guess thats how helical oil seps achieve 99.9% separation.

I'd stick with the Temprites too...

Tom

[n00b 0f l337]

Now how to replicate the spinning I guess if I run out of temprites (doubt it).
Cheap copper spun accumulators? Pull out the mesh and drill in from the side?
http://cgi.ebay.com/PARKER-2-1-2-x-7-Accumulator-12141_W0QQitemZ7606675048QQihZ017QQcategoryZ42911Q QrdZ1QQssPageNameZWD1VQQcmdZViewItem

[[XC] 2long4u]

//Brasing aluminium to copper?! How the hell does that work? :confused:

Don't know. Did you watch the video?
You guys should talk to Dyson.

[SoddemFX]

Maybe, they look what i'd think would be the ~ right size. Not sure how you'll pull out the inner without weakening the shell, it's probably not rated too high pressure wise either from its intended use. I guess you'd have to work out something. I don't think you'll run out quickly with 24 tho :D

Tom

//2long4u - I don't know, i haven't looked it up but i didn't think they were metallurgically compatible :confused:

[[XC] 2long4u]

What about an aluminium tank with o-ring fittings?

[n00b 0f l337]

http://cgi.ebay.com/PARKER-2-1-2-x-7-Accumulator-12141_W0QQitemZ7606675048QQihZ017QQcategoryZ42911Q QrdZ1QQssPageNameZWD1VQQcmdZViewItem
Theres your solution.

[Derek]

http://cgi.ebay.com/PARKER-2-1-2-x-7-Accumulator-12141_W0QQitemZ7606675048QQihZ017QQcategoryZ42911Q QrdZ1QQssPageNameZWD1VQQcmdZViewItem
Theres your solution.

That looks perfect... I didn't even think to search for an accumulator! I'm going to buy it but I'm going to make my homemade separator since I already have all the stuff for it (what else am I going to use 5' of 1" tubing for?).

I got parts for a small SLHX today too, going with a 1" outer shell and inner shell corrugated copper. About 11" length. I'll place it before the separator to help with separation.

Just for restriction, should I do like 1/4" tubing for the gas side of the separator and 3/8" for the bottom? Or is that not enough restriction on the top?

[Derek]

After thinking some more, for a restriction on the top tubing (for the CO2) how about I just pinch the opening of the tubing making it smaller? This should make the pressure from the first chamber transfer to the second one more-so through the liquid (r22) line rather than the gas (co2). Obviously if I pinch it too much the problem would be reversed, there'd be co2 that might be forced into the r22.

On a completely unrelated subject, does anyone have a pressure/temperature chart for co2 that also contains the phase states? That would help a great deal in preventing sublimation. I'd like to get as close as possible to the triple point while I'm tuning.

Edit -- found what I was looking for: http://www.chemicalogic.com/download/co2_phase_diagram.pdf

Further edit -- after studying this, basically what I need to make sure of, is that once the co2 is evaporating (from liquid of course) that the low side pressure is low enough that I don't have dry ice forming. Which leads me to my next question... Is having a little bit of R22 in the low side to help move dry ice along good, as long as you don't have any (gaseous) co2 in the high side? I specify "gaseous" b/c obviously if a little co2 condenses in the SLHX and goes into the high side it should only help things....

[n00b 0f l337]

The annoying point is that most peopoles experience shows your stuck around -58C unless you can get something in the mix with the co2. Damn the triple point.

[Derek]

The annoying point is that most peopoles experience shows your stuck around -58C unless you can get something in the mix with the co2. Damn the triple point.

So here I am trying to get the best phase separation I can but in reality it will just hurt me when using CO2. I want a little of the R22 in with the CO2. I'd rather not run a line of R22 to the evap from the phase separator b/c that would dump oil into the evaporator and then I might have problems with oil freezing/oil is an insulator so it'd hurt my temps on that front as well.

I read through some of LukeXE's posts saying that one solution is that you just dump a lot of R22/propane into the system (aka, forcing some of the high side refrigerant in with the co2) but with the excess refrigerant I'm sure it must hurt the main HX temps. Is there any way to design the phase separator so that the liquid side is only liquid but the gas side gets a little bit of R22 in it without overcharging?

[n00b 0f l337]

Well yeah, I"d imagine if you moved the gaseous output on the phase sep downwards more, it would get more liquid.

[Derek]

Double separator did not work. Using the accumulator NoL link to above now. A note for anyone else buying one though, they're steel not copper.

[mytekcontrols]

Using the accumulator NoL link to above now. A note for anyone else buying one though, they're steel not copper.

Yes I just found out the same thing myself. Apparently they ran out of the copper version and substituted a steel one manufactured by Carrier. For its intended use as an accumulator, either one would work fine, but to modify as a phase separator, it becomes not as easy (much easier to drill a hole in the side of a copper tube and braze with silfoss, than it is to drill steel and have to silver solder). It would have been nice if the Ebay person had contacted me as to the change, before taking my money and shipping the alternative part.

Oh well, life's like that sometimes :rolleyes:

[Derek]

I actually took apart the steel accumulator and it looks like if you drill a hole to the side of the center one on the bottom (the gas output) it will work for the liquid output. The center output on the bottom will be gas and it also has a hole for oil return (which in this case would allow R22 into the CO2 side of the system) and I think it should let just enough R22 to help with sublimation.

The screen @ the top I'm assuming turns fine misted R22 into droplets, but the center section is blocked and covers liquid from exiting the gas side.

I'm going to try it for my separator and hope it works... If not I'll just build a single 8 x 1" tube for my separator with copper wool near the top gas exit.

On an entirely unrelated subject, my berkut style hx seems to be collecting huge amounts of oil in the R22 side -- any tips? I guess I haven't added Propane yet, should that fix the problem?

[[XC] 2long4u]

You don't need silver solder to braze copper to steel.

[Derek]

I'm having trouble getting the heat exchanger cold. The hx R22 exit gets down to about 4-5C and the evaporator gets down to about -50C. Using the same compressor I got down to lower temps on a single stage!

High side pressure was about 225 psi, low side about 20 psi. I played with the charge a bit and no matter what I did I couldn't get hx temps lower -- it's like they just froze @ 4C.

The way I charged was 60 psi static R22/R290, and 60 psi static CO2. I started the system and did a little R22, then a little CO2, etc. I have 8' .031 cap tube for the hx, 9' .031 cap tube for co2/evaporator. I'm using a pretty good sized R22 compressor made by Americold. Can't find any info on it but it has 6.9 FLA and 34 LRA so I figure it's at least 3/8 hp. Other than the low hp on the compressor the rest of the build is solid -- large steel condensor, accumulator for the phase separator, a 2 foot long berkut style hx, and a suction line hx. Both heat exchangers were made with 3/4" corrugated copper inside a 1" copper pipe, and of course the main hx has the suction line running through the middle.

Anyone have any tips?

[n00b 0f l337]

Most likely the following.
1) Your undercharged
2) Definitly undercharged with your high stage gas (r22/r290)
3) Aux condenser/SLHX?
4) Aux refrigerant?
Your undercharged, but you think your not becuase your pressures are high as it is. ;)

[[XC] gomeler]

Agreed with NoL, honestly just dump what you would think to be an ungodly amount of r290 into the system. I was amazed at how much r290 my autocascade used compared to my typical r290 single stages. The pressures really won't rise much while you are dumping the r290 but the CO2 will really bring up the discharge pressures so be careful and always make sure your static pressure isn't nuts. Goodluck :)

[n00b 0f l337]

With autocascade, you should charge every refrigerant at static.
The main thing is you arent using a high boiling point refrigerant, that will massively bring down your discharges. WIthout it, your pressures are going to stay high, and to get where you need to be you might need 275-300 psi high side at norm (very hot compressor discharge with that), and then some.

[Derek]

I'm running about 10% R290 and 90% R22 as was recommended earlier in this thread. I'm going to dump some more R22 in there and see what happens!

BTW guys, thanks for the quick replies!

[n00b 0f l337]

I can tell you now, your pressures will go up, your high side will get hotter (especially at discharge), and you'll be stressing compressor more. I dont think your really autocascading yet. Sure your temps show youve got some co2 condensing, but nothing big yet.

[Derek]

Okay, added a bunch more R22 and the following has happened:

HX temp has gone UP to 8C.
Low side pressure has gone UP to 25-28 psi.
High side pressure has gone DOWN to 200 psi.
Edit - Forgot to mention, Evap temp up from -50 to -38

????

Keep adding R22?

Add a little CO2?

Release a little CO2?

Cry? :( :shrug:

[Derek]

I keep adding more R22 and HX temps are slowly dropping (at 2.8C now) and suction line pressures are up to 32 psi, but high side is down to 180 psi.

edit HX @ -6.3C now. 35 psi lowside 185 psi high side.

2nd edit HX exit @ -8C now. 36 psi lowside and high side has actually dropped again to 175 psi...

Man this thing is acting weird!

Should I ignore low side pressure and tune to the HX temperature and then add CO2 for evap temps after that?

[wdrzal]

You don't need silver solder to braze copper to steel.

What do you use??????

[Xeon th MG Pony]

He's in auto motive, can't recall the name of the epoxy material but it is a bi metal epoxy.

[Derek]

Meh, still no luck in tuning this beast. I'm @ -40 on the evaporator, -8 on the exit of the heat exchanger, 225 psi high side 40 psi low side.

I'm betting that my compressor just isn't strong enough and can't pull enough of a vacuum for lower temps. =(

Would trimming cap tubes help? Again, HX is @ 8' and evap is @ 9' both .031.

I might just scrap this and go back to my SS if I can't get this thing to perform correctly. I've got a rotary I could throw in to see if a stronger compressor makes a difference for me but there's no room in my computer case for a rotary compressor so it'd be a short term thing.

[n00b 0f l337]

Nope, your getting closer to your true HX temps. But right now you have r22 going the co2 route as well. Add even more r22, then add co2 when your hx temp gets to about -20C. Forget about the suction pressure for now.

[Derek]

After tons of help from NoL via MSN, I've finally gotten my unit tuned...

Sorry for the lack of pics, I'm without a digital camera, but here's some old ones of my compressor (which I'm told is probably about 1/3 hp):

http://i30.photobucket.com/albums/c333/DerekRH/PICT3435.jpg

http://i30.photobucket.com/albums/c333/DerekRH/PICT3440.jpg

Anyways, with 300 psi high side, and 55 psi low side, my hx is @ -9.5C and the evap is -35.6C.

Definitely not the best temps but I think with a HX upgrade and a bigger compressor I'll be getting somewhere!

[n00b 0f l337]

Definitly autocascading, possibly still even undercharged though for a load. Larger HX's, larger condenser (or aux condenser with high boiling point refrigerant) would lower your high side as well.

[wdrzal]

After thinking some more, for a restriction on the top tubing (for the CO2) how about I just pinch the opening of the tubing making it smaller? This should make the pressure from the first chamber transfer to the second one more-so through the liquid (r22) line rather than the gas (co2). Obviously if I pinch it too much the problem would be reversed, there'd be co2 that might be forced into the r22.

On a completely unrelated subject, does anyone have a pressure/temperature chart for co2 that also contains the phase states? That would help a great deal in preventing sublimation. I'd like to get as close as possible to the triple point while I'm tuning.

Edit -- found what I was looking for: http://www.chemicalogic.com/download/co2_phase_diagram.pdf

Further edit -- after studying this, basically what I need to make sure of, is that once the co2 is evaporating (from liquid of course) that the low side pressure is low enough that I don't have dry ice forming. Which leads me to my next question... Is having a little bit of R22 in the low side to help move dry ice along good, as long as you don't have any (gaseous) co2 in the high side? I specify "gaseous" b/c obviously if a little co2 condenses in the SLHX and goes into the high side it should only help things....

IIRC CO2 @ freezes @ -58.C and sublimates @ around -78.5C

CO2 is not a good gas in this state because of this.

[[486]]

What do you use??????

He's in auto motive, can't recall the name of the epoxy material but it is a bi metal epoxy.

normal brass [bronze?] rods, or 15% silver is lower temp than the brass