Choosing compressors for cascade (EXPERTS NEEDED)

[Shankara]

Hello,

I've been planning to build a cpu cooling system for some time now, I've looked around for the best compressor technology and sadly Stirling isnt mainstream yet : why ? everyone says it is the highest efficiency cycle existing so why ? So of course, for our budget and size, the only choice we have is cascade compressors...


I've been planning to build or get myself a 2 stage cascade. I'm thinking of buying the best compressors I can get because I think it is the most important part of the system, as cooling capacity at any temp will be determined by compressor efficiency and power.

(Am I correct ?)

** I'm seeking for compressors with *highest* efficiency for a given weight / noise / size (and of course power cosumption, but this is included in the term "efficiency" obviously).

** 1rst stage would probabably be R407c, R404a, R507 or anything better to suggest (which is better, best cooling cap ? I think R134 is out of the question since R404a alone is > 30% higher capacity... but what about Hydrocarbon 1rst stage refrigerants ? Are they any better than those I named ? )

** 2nd stage would probably be R1150 (Ethene). (Anything better ?)
(other choices are R508b ? but higher evap temp - -88 C -, but maybe same cooling cap then ethene at that evap temp )

* What is the difference in semi-hermetic and hermetic compressors ? Some say semi-hermetic are more efficients, while Tecumseh claim the contrary on one of their model...

*** (!!) Are rotary (you know, those compressors that look like cylinders that berkut used I think) better than "conventional fridge" ones ? (I think the later are called reciprocating compressors ?)
I'm tempted to think rotary is less noisy and more efficient and longer lasting ?

Here are the models / company I've "tried" browsing. (Comments would be appreciated! Thank you! )

TOSHIBA:

Toshiba seems to have put together an helical compressor at a decent size (not like the scroll behemoths in industries). It was announced in 2002 I think, but I haven't been able to find any info on that !! Any clue ?

TECUMSEH:

Their newest model is an Horizontal Rotary Compressor aimed at replacing semi-hermetic compressors for display case and supermarkets.

http://www.tpc-nacg.com/rotary/prodTour.htm

Supposed to have a 30% efficiency increase for same weight ! (This seems very nice, do they have 1 HP or at least 3/4 HP models ? Can it compress R1150 ? )

CAR A/C Compressors:

Kuehl, Seiko, etc. rotary compressor

Needs motor with belt but small, light, quiet, but not a lot of power I assume, and expensive too... (350$)


** Most company have rotary ones: Copeland, LG, etc.

** ABOUT POWER :

My application would be a 2 compressor dual cascade with dual evaporators (so a split discharge and 2 recombining suction ?) (this is for dual CPU cooling). I think 1 HP + 1 HP would be good ?

See, I think I should aim at about 350 WATT cooling power at -90 to -100 for 2 CPU (especially taking into account 90 nanometer Xeon which should deliver much more heat, like Prescott). I know commercial lab recirculation systems like the NESLAB ULT95 uses 2 x 1.5 HP compressors to deliver this, but I assume my application would be more optimized (considering gases used, compressors, etc. )

* I'm aiming at around 150 LBS max (?) for the two compressors combined...



Can anyone help ? I think this would help a lot of other people trying to get the best no ?

Thanks a lot,
Shank.

.oO( Invoking guru's out there, Chilly1, Gary, etc.
:worship: )

[Beccara]

Have you built PC systems before?

[Apoc]

If you want to build a cascade system and call r1150 'ethene' you may just have a slight problem when trying to build said system.

Ethylene can also be called Ethene..

[Shankara]

I've been considering this for 2 years now. I almost bought a lab surplus -90 loop before because I knew a friend working at a biotech incubator company. As for myself I work as a researcher in a university (in math obviously not in chem otherwise I wouldnt be there) but I figured it would help to ask here.

I know all about other cooling methods, if I posted here it's because I was interested in info on double compressor phase change. I don't want a one stage system, for me it's worth much more to build a 2 compressor setup once you're considering PC... of course I'll have to build one stage first anyways. I'll probably ask for help here and there.

350 watt is the capacity I'm aiming at, and my other post is exactly what I was asking: what compressor suits me best regarding the constraints I've raised (noise, size, weight, efficiency).

And about R1150 : look at MSDS's :
Trade Name: Ethylene Chemical Name: Ethylene Synonyms: Ethene, [...], refrigerant gas R1150

It is called ethene too, so I don't see where's the problem in me calling R1150 ethene...

(And if you find my spelling or english weird, I'm sorry about that, I'm french)

Thank you,
Shank.

Originally posted by leviathon
My question entirely. Sorry about this but it needed to be done, 1 cascade is not the only option we have out there we have eveything from aircooling through to the more extreme like 'phase change' 2 If you want to build a cascade system and call r1150 'ethene' you may just have a slight problem when trying to build said system. 3 In my and others opinion you should probably start by building the rest of your system to the specs that you want '350Watt dissipation' then find out what compressors work best for it.

This is in no way ment as a flame, just some advice that you do not have to pay attention to in any way

[Sidewinder]

I would use hermetic rotary compressors, you dont need a semi hermetic.

You were asking whats the difference... well, there a 3 types of a case for a compressor.

hermetic - compressor and engine in one case, good for "small rigs" (refrigerator, computer etc.)
semi hermetic - used in bigger systems, engine and compressor are one unit. Its advantage is that the axle does not have to be sealed against the engine. If a leakage in such a seal up comes up, its only very difficult to repair.
open - used in huge Systems and NHS Systems. Engine and Compressor are 2 pieces, u can run it with a drive belt or so.

[chilly1]

Ethane= R170, CH3Ch3
Ethlyene=R1150, CH2=CH2
Both will work as second stage refrigerants however R1150 has a lower boiling point.
Proplyene R1270, CH3CH=CH2 can be used as first stage, You will want to add a little R290 (Propane) to lower the head pressure. R290 can be added to the other refrigerants to facillitate oil return also..
350W at -85 would be possiable with a sc12mlx (thats a 115V danfoss) it is a R404/507 compressor. Rotarys do have a few issues as cascade rigs mostly is the topend lubrication as the oil/ refrigerant blent is the seal in the compressor it is nessassary to use an oil seperatio that will provide a constant oil stream in the suction line. I prefer rotary Vane compressors I have only been able tofind one in the past year, americold used to manafacture them but since whirlpool took over the line was discontinued. Semihermatic compressors woill handle extremes of operation better than a hermatic compressor. Oil is also critical in the first stage using R507 the oil shold be polyolester sus150 and the second stage or low temp side the oil should be sus100. You may want to rethink teh dual cascade thing it is difficault to balance. I am fighting one now... Runs well at -68C on both evaps it is for a northbrige and memory.. needs more tuning. .

[Sidewinder]

hmm yeah SC compressors are pretty nice but it will be difficult to find used ones, i think u have to buy em.

Hmm what are rotary Vane compressors? Could you translate it in German? Never heard that

[HawainPanda]

wow...350 watts..i don't think a cpu and gpu together would ever produce that high...chilly 1, is there a particular reason u use danfoss for many of ur work?

[saratoga]

prefer rotary Vane compressors I have only been able tofind one in the past year, americold used to manafacture them but since whirlpool took over the line was discontinued.

Offtopic: Do you have any info at all about Americold? I can't find specs on any of their parts, and I've got one of their compressors handy.