Can someone explain multi-stage cascades to me?

[js530]

From what I've read, R507 will be too high of a temperature for second stage. But R507,R404 will work better than propane, but they are many times more expensive than cheap propane. Finding an oil that will work at -190C will be difficult....

[gclg2000]

someone played w/ methane. don't think it held load very well.

[skate2snow]

No, methane has a very low load capacity...... To hold his low temp you would need a compressor in the 5hp range which would make blink the lights of all your city....

And for Helium, isnt helium a suprafluid? If so, a compressor will not work with "liquid" helium.....

Try to just stay with a typical R404/507/402 and Ethylene (Not all of those gases, either of those...) Ethylene is pratically a "perfect" single stage gas due to his property... For third stage, its hard to find even the "pros" Dont really have a very nice gas, but the one that works best is R14.... But often hard to find...

[Skinny13]

so I quess I can put 404 in the first and 507 in the second...

what temps will I get at the evap?



=========

may this sounds funny but sticky vote for this thread
so many months I see HX and stuff like that and I couldn't understand
now almost everything is clear

[MutantToad]

Yeah, this would make a nice sticky...

Anyway, does anyone have a list of refrigerants and their boiling points (and if you need a certificaton ?) I still don't know the boiling points of R507, R404, and a lot of other refrigerants. Also, where can I get HX's?

Edit: Forgot my sig, lol. ~Toad

[js530]

http://www.wc101.com/guides/refridgeration/page6.htm
This website has alot, and mainly those used in processor cooling.

[MutantToad]

I already read that . How coincidental. But it doesnt have R507!!!

~Toad

[MutantToad]

Ummmm...

bump

[HungryForHertz]

Bumpo. A good thread. Good sticky potential.

[GuGaCoSa]

I think you can get something close to -70/-75 without load on r507,if you want a low cost second stage gas i would go for r410a that has a lower boiling,or co2 + r290 or r22 to carry oil and prevent cap tube clogging

[MutantToad]

Hey, look everyone, this thread has been bumped!

Anyway, skate2snow, how could ethylene be a "perfect" 1st stage gas? I mean, doesn't it have a boiling point of -104 degrees C? And that's a bit low for a single stage?

~Toad

[saratoga]

Hey, look everyone, this thread has been bumped!

Anyway, skate2snow, how could ethylene be a "perfect" 1st stage gas? I mean, doesn't it have a boiling point of -104 degrees C? And that's a bit low for a single stage?

~Toad

Given that he listed first stage gas twice, and then went on to third stage, I think he meant to say 2nd stage. Obviously you can't use ethylene for a first stage.

[MutantToad]

Good point. Man, I should really use my head more when reading these posts....
Anyway, I've searched, but found little about building inter-stage heat exchangers. Does anyone know of any links out there about building them? Much appreciated.

~Toad

[GuGaCoSa]

There is a nice link in teampuss forums : http://www.teampuss.com/forums/viewtopic.php?t=245 (Suction HX's)
http://www.teampuss.com/forums/viewtopic.php?t=219 (Interstage)
5m of 1/4" tube inside 1/2 tube will do the job nicely

[pythagoras]

You mean you missed the ultimate Hx construction guide :

http://www.xtremesystems.org/forums/...054#post798054

Regards

John.

[MutantToad]

Thanks pythagoras, that was a good (and entertaining) read. But.....I still don't know how to get 2 pieces of tubing inside one another. Which refrigerant (1st stage or 2nd) should go in which piece of tubing?

And a bit off topic: What exactly is the point of a desuperheater, chilly1 said something about it increasing efficiency, and how would I make one?

Sorry for not knowing so much about phase change, but hey, we were all noobs at it at one point in our lives (except a handful!)

~Toad

[saratoga]

Thanks pythagoras, that was a good (and entertaining) read. But.....I still don't know how to get 2 pieces of tubing inside one another. Which refrigerant (1st stage or 2nd) should go in which piece of tubing?

And a bit off topic: What exactly is the point of a desuperheater, chilly1 said something about it increasing efficiency, and how would I make one?

Sorry for not knowing so much about phase change, but hey, we were all noobs at it at one point in our lives (except a handful!)

~Toad

Its easy to get tube inside one another. Just cut one longer then the other, and slide the narrow/longer one inside the shorter/fatter one. Then install T fittings on the ends of the fatter one. Finally braze the ends of the fatter one shut around the shorter one. Another way that I've done is to put end caps on the fatter one, and drill holes in them. Then put reducers on the smaller one. The neck of the reducer will sit flush with the edge of the cap and you can braze that together for an extremely strong seal. Either way will work.

[MutantToad]

So... it would be something like this:

http://img299.imageshack.us/my.php?i...changer2cf.png

Is it the one on top, the one on the bottom, or neither?

~Toad

Edit: If the image is too small, just refresh the page. It works for me. If you don't have that problem, you can ignore this.

[js530]

I would use R290 (propane) > CO2 (with R290 to tune it) > R50/CO2 mix (Methane, bp -160, easier to get and cheaper than r14) > R740/Methane/CO2 Mix (r740-argon) > and then air as an open loop refrigerent. None of these gases are restricted, so they can be mixed as required, and vented into the atmosphere. The air would be condensed (200-400 PSI) in an HX, and then go through an expansion valve, where a mist of liquid air/gaseous air would be sprayed into some insulated container (styrofoam cup? ). The air must be "scrubbed" first, where the CO2 is removed using calcium hydroxide. Then, it will need to be dried, possibly using calcium chloride. This is all done before the compressor, and the chemicals will have to be occasionally replaced. CO2 and moisture will freeze in the expansion valve, stopping the flow of liquid air.

If I get the money, I would definately make a 5 stage nitrogen liquifier Of course, after I get some practice building some smaller cascades.

Some calculations (rough)
200 watts of heat removed from the nitrogen would be able to condense just over 1 liter per hour, which is horrendously slow. This isn't even counting how much heat you have to move just to lower that nitrogen to near its boiling point. Even small nitrogen liquification plants (lab sized) deliever around 10 liters per hour. Best bet would be joule thomson expansion combined with a two stage cascade, so compress the air to around 2,000 psi and then cool it to -70. Let it expand and precool the incomming air and it should eventually liquify.