simple cascade questions

I have transformed this into a worklog- skip the boring talk and go the the end for some piczles



hey!

first off, i will ignore any post saying im not ready for a cascade. i know im not. once i get 2-3 units built and properly tuned, then i want to try a small, daily cascade, hoping under 1kw consumption. also summer boredom might kick in:yepp:

I was thinking of using a nl11fx (hence the thread in the wanted section) and a ne2134gk(first stage). Would like to use ethylene, but might be a little hard on the smaller compressors. How much are temps affected by using a very small amount of r290?(i mean just static charging with 1150, then tuning with 290 for safety?) Could i use straight r1150 if used a high pressure first stage gas? r410a in first stage with large condenser+300cfm fan+watercooled dsh should help with r410a(maybe blend), and get cold enough to condense 1150?

Do you guys think this would be possible or not? i am thinking most likely a cap tube system on both stages, but open to valves.

Really just wanting opinions to think if i should just stop thinking about it as this small of a build won't happen (want to build a more economical unit then rotary cascade). i have most of parts here for build such as: ac and r floated oil sep, 10 plate hx(2 of em), danfoss kb-7 hpco(11 of em), gauges(covered), either 8x10x2" condenser(from detroitac) or a larger version of it, aspera ne2134gk compressor...
which is why me wants to build it.

So thoughts and advice greatly appreciated(especially safety)

regards

Teyber, I think you can do just about anything you set your mind to.

Pickout a build you like and go for it, taking all the advice you can get.

My the force be with you :)

Coming from a guy that built a 1/6hp cascade, 1/3hp cascade, and then a 3/4hp cascade, the 1/3hp will be great to learn on but terrible to bench on with heavy loads. An E8500 and E8400 would probably have a field day on an NF11FX based build but any QX/Q would slaughter it. It'll be a good learning experience but if you plan on benching, it can be most frustrating when you don't see that magical -100C evap temps and such but you learn to accept your cascade for who it is :p: I used R507/R1150 and it's worked fine, just make sure your 1st stage condenser is large enough to reject the entire heatload plus some wiggleroom or else your HX temps will be too high and screw up the 2nd stage pressures. A simple cascade isn't that hard, especially with a floated oil separator. Just use the right safety gear, triple check everything, and purge everything.

thanks buckeye!

gom: definately not for benching... maybe a rotary cascade next but just something daily for my q6600 at not crazy clockspeeds. for first stage, was thinking a smaller condenser (same as on my rotary build) but a water cooled DSH(and by dsh i mean plate hx and 360mm rad...)

also mate, guessing the ne2134gk will be a bit cooler then a nl11fx if im correct? id love get a noload -100c just for kicks then tune it, hoping for maybe -70c or so load. Not to big expectations on this unit here.

thanks for quick responses guys. what do you think about 1150 vs. r290/1150?

getting a quote 2maro... last person to help me at my airgas, who doesn't really cut me deals said 190$ for 10cuft, 220$ for 35cuft, and 310$ for 200cuft. i think ill get the 35 cuft, but a really nice guy who always helps me out is giving me another quote 2maro. im just trying to not get raped by the bottle...

Regards

NE2134GK is not a very good compressor at high pressure ratios (like you'll need to run).

The NEK2134GK is very good.

Check the datasheets of your compressor options before you make a decision. They all cost in the smae ballpark, but performance at high PR varies widely.

thanks tom!

ill start some research on a good TEV for a small cascade. I haven't often come across a r507a or HFC TEV for our small loadsd. I have two 10plate hx's here. No r404a here, but ill give r507a a shot. just thought it may not be enough to condense it? but the ne2134gk are great little torque monsters.
Ill be on the lookout, i think a sc12 or so in first and the aspera compressor as a second stage would be a lot easier, but i think this will be fun. I don't have kw ratings on the condensers i have, but ill post a pic 2day afterschool. Also i will be using a 500cfm fan on it.

I got the AC and R oil sep on a best offer on ebay for 25$(actually 2 of them for 50$), just wondering if they will even work.

Will an expansion tank be necessary or will the 2 large accumulators i will use be enough?

also about tuning a cascade, do you just rough charge first, finish up second stage, rough charge second then fine tune? it seems a lot of people fine tune the first while say vacuuming or pressure testing second, but im not sure how you would do that.

thanks for the nice lengthy response mate!

regards

detroitac- we posted at same time.

i thought the K version was just more silent and efficient, maybe even less powerful(not sure here though). Thanks for the heads up, don't really have an option though unless i want to use a rotary or try to snag up a different first stage and move this to the second.

regards

Good morning guys. I thought I would see whats going on here before I went back to sleep. :D
It would be fun to make a little cascade. I have a compressor out of an old refrigerator and a very small one out of a water cooler. I don't know what it would be good for except just messing around with it. Maybe at party's see how long you can hold your tongue to it? :shrug: :rotf:

It's a really complicated thing, and there aren't any generalizations or rules of thumb about these small hermetics. You have to rely on what the datasheets say about performance.

At the Embraco rating point their capacity is about the same, they must use a part numbering system like Tecumseh, in that the capacity is built into the part no code.

The NE is a ~12cc compressor
The NEK is a ~9cc compressor. At high pressure ratios the NEK outperforms the NE by 2.5X :shocked:
:fact: embraco datasheet

Whoops, I read your intent wrong. You only want -70C loaded, so your pressure ratios (if they are balanced) will both be ~5 or so with 507/1150. They will be different depending on the relative sizes of your 1st and 2nd stage compressors, but in any case, the NE works just fine in that range :up:

Quote:

---

Originally Posted by teyber

thanks tom!

ill start some research on a good TEV for a small cascade. I haven't often come across a r507a or HFC TEV for our small loadsd. I have two 10plate hx's here. No r404a here, but ill give r507a a shot. just thought it may not be enough to condense it? but the ne2134gk are great little torque monsters.
Ill be on the lookout, i think a sc12 or so in first and the aspera compressor as a second stage would be a lot easier, but i think this will be fun. I don't have kw ratings on the condensers i have, but ill post a pic 2day afterschool. Also i will be using a 500cfm fan on it.

I got the AC and R oil sep on a best offer on ebay for 25$(actually 2 of them for 50$), just wondering if they will even work.

Will an expansion tank be necessary or will the 2 large accumulators i will use be enough?

also about tuning a cascade, do you just rough charge first, finish up second stage, rough charge second then fine tune? it seems a lot of people fine tune the first while say vacuuming or pressure testing second, but im not sure how you would do that.

thanks for the nice lengthy response mate!

regards

---

It never hurts to have a capillary attached expansion tank. I put a huge one on my system and my statics sit around 125psi on the 2nd stage and I have a tiny post-HX section so with a larger post-HX area the static would be nuts.

As for tuning, I'd just get the 1st stage so that it's running the pressures of a similar sized single-stage set for a heavy load. I run at idle 3psi suction and 210psi discharge and under load it jumps to ~8psi suction and 245psi discharge. The second stage I just static charged to 100psi and then dialed it in while monitoring the 1st stage and HX temps. It'll take a good bit of tweaking to get it running perfectly but you can get close with little effort. Need a larger condenser to drop that discharge even more but the compressor happily churns away without any excessive noise/vibration/heat. As always you have to tune to your setup but this just gives you an idea.

perfect :D

2long4u: if you wanna drive down for some ethylene come on down :D

waiting for a callf rom my airgas. 220$ for 35cuft sounds good to me. I asked how many lbs is that and both guys had no clue. hoping i can swap my co2 tank for the tank of ethylene+ some cash... i hate renting, and they have done that for me in the past.

are hydrogen regulators cga 580 fittings? i have a 580-350 adapter already (For co2), would that work?
and i know that charging with ethylene while unit is running is a big NO-NO, but im not seeing many h2 regulators that have a discharge of higher then 100psig. and the ethylene regulator from airgas was 750$ LMAO

detroitac: sweet. had me a bit worried. i understand the nek is newer and better, but the deal i snagged on ebay as the ne... 20$ with reasonable shipping :P(new with electrical included)

gom: thanks! yeah obviously its tricky, tuning a cascade sounds very time consuming but i have all day for 3 months :D just wanted a starting point, thanks for the advice.

There seems to be a liquidator of expansion tanks on ebay, however they seem quite large and have a max psi of 100psig...
how big would you guess is best?

safety will be #1 on this build so all safety precautions will be taken, high pressure cut off in first and second stages, gauges in first and second stages(high side), and most likely a pressure relief valve in second stage but need to do more research on how they work, internals et cetera.

ill snag some pics now.

regarsd

A pressure cut off can only shut down a compressor (normally). There ARE situations that pressure can still rise with the compressor off. Always use a pressure relief valve on the second stage of a cascade,if ones pops they don't release as much gas that a fart has & your back down to a safe working pressure.

BTW Be sure it's resettable, some have a burst plate that doesn't reset.

k took some pics.
http://img513.imageshack.us/img513/7...ffsofaruc3.jpg
http://img513.imageshack.us/img513/7...e83bd82b09.jpg
what i have so far.
http://img170.imageshack.us/img170/4...tyboxeski9.jpg
http://img170.imageshack.us/img170/4...394bc7777e.jpg
hpco's
http://img91.imageshack.us/img91/637...sersideyv0.jpg
http://img91.imageshack.us/img91/637...3b737c7ec6.jpg
condenser, its not layed out correctly but i think it might do
http://img363.imageshack.us/img363/4106/safety1qt4.jpg
http://img363.imageshack.us/img363/4...1627233a66.jpg

regards

Quote:

---

Originally Posted by wdrzal

A pressure cut off can only shut down a compressor (normally). There ARE situations that pressure can still rise with the compressor off. Always use a pressure relief valve on the second stage of a cascade,if ones pops they don't release as much gas that a fart has & your back down to a safe working pressure.

BTW Be sure it's resettable, some have a burst plate that doesn't reset.

---

sorry we posted at same time.

How much do they usually cost? out of curiosity. there are some on ebay, new ones that are not expensive but im not sure if they are resettable.

thanks for posting mate:up:

Highly Flammable.........The USA hasn't warmed up too gases with a low LFL in air. (lower flammability limit)

Quote:

---

Originally Posted by SoddemFX

Why does no one use ethane much? It looks good.

---

Because R23 is much easier to get and cheaper (in Germany).
And of course non flamable.

Quote:

---

Originally Posted by SoddemFX

Hi Erik,

For -70C i think the only way he would be able to do this with this system and ethylene would be developing massive evaporator superheat. Set up well i think it should be capable of much lower.

To achieve a -70C Tsat with ethylene would need 4barg suction pressure, which would probably overload the compressor (i'm guessing?) but it would definitely cause the discharge pressure of the second stage to go skywards, because the 1st stage wouldn't handle the condensing load which would be developed from the mass flow in the second stage with 4barg of suction pressure.

---

Good point Tom, but I've run some calcs and don't see superheat being able to change the situation much, nor SLHX. Seems to me the motor will be just fine @-100C evaporating temperature, but overloaded @-70C no matter what superheat exists. It would be about 2X the motor power that an LBP R507 compressor is sized for. :down:

Condensing pressure would be high (~350 psig), but I guess that didn't worry me since it's a hard piped loop. I don't think the load would have been a problem, but the 2nd stage compressor motor wouldn't have been happy.

Shucks Teyber, are we taking all the fun of designing this away from you? Or perhaps this is all part of your evil master plan to get the phase forum to design your system?

Edit: Coincidentally, this is the same problem with using 410a in a compressor that isn't designed for it. A 507 compressor has less motor power per displacement than a 410a compressor, so although 410a would work at LBP conditions, you'd need a compressor designed for it, otherwise you have an unhappy motor. It's not worth running 410a and having an overheated motor or running 507 (@ the compressor's design conditions) for the ~same cooling result.

maybe i phrased this wrong, im just going for lowest temps i can get while holding load. as long as its a fair bit cooler then a huge single stage ill be pretty happy, but ill be tuning for coldest temps depending on wattage on cpu at the time.

i haven't looked over a 1150 p/t chart yet, so not sure what is viable yet. probably should have done that before i started the thread :P

Regards

Ethanes wonderful, but expensive and can be harder to get, but you are right, we should all be using that or r23 or r508a or similar, not making the jump to ethylene.

ethane just seems like a ethylene but with a warmer boiling point, don't know much about the specific heat of it vs. ethylene, but seems almost as dangerous, et cetera.

r23 i understand but someone wanna elaborate?

regards

Simple cascade questions eh?:rolleyes: Seems cascades are not very simple.

I do take your point Tom, that if you are trying to hit -70C that is one way you could possibly do it.

Really Teyber, it's a bit of a shot in the dark way of designing a cascade to say you have picked two compressors and the gasses and just want as cold as possible. Don't get me wrong, cascades are built like that all the time here, and it will function I have no doubt. To build it without understanding what will happen or why, I think you could spend your summer doing that, and by the end of the summer have a bit more experience. I don't have an alternate suggestion really. I don't think you would be allowed to sit in a Thermo course at some local univ. as this is pretty much senior level undergrad mechanical engineering stuff. I certainly wouldn't have had the skills at 16 to do it, but perhaps you're a refrigeration prodigy?

Ethan is a great second stage refrigerant but involve higher condesing rejection for a given cooling capacity than R23 does. And the other hand ethan and propan have similar "pressure properties" : large temperature range between two pressures points. The excess load would lead to higher HX temperature but the discharge pressure won't increase a lot :)

Here's a table I made for Baz, you've got the Rejection/capacity for serval -8x's gases

http://clemmaster.free.fr/2nd_stage_refrigerant.jpg

Quote:

---

Originally Posted by DetroitAC

Simple cascade questions eh?:rolleyes: Seems cascades are not very simple.

I do take your point Tom, that if you are trying to hit -70C that is one way you could possibly do it.

Really Teyber, it's a bit of a shot in the dark way of designing a cascade to say you have picked two compressors and the gasses and just want as cold as possible. Don't get me wrong, cascades are built like that all the time here, and it will function I have no doubt. To build it without understanding what will happen or why, I think you could spend your summer doing that, and by the end of the summer have a bit more experience. I don't have an alternate suggestion really. I don't think you would be allowed to sit in a Thermo course at some local univ. as this is pretty much senior level undergrad mechanical engineering stuff. I certainly wouldn't have had the skills at 16 to do it, but perhaps you're a refrigeration prodigy?

---

sorry to revive this thread... but yeah, ive tried sitting in on courses before and they don't like it... and there arn't really a lot of engineering schools around me. thats kind of exactly how i plan to build it:ROTF:

I think that im just going to make 2 singles with these two compressors and use two sc18clx.2 compressors...

regards

sorry for poor quality pictures but compressors came today:up: about 500 sc18clx.2's fell of a shelf. i got these for a helluva deal... i mean incredible:eek:

cosmetically they are poor. the feet are bent and have lots of scratches. one of the plugs came of fin transit so ruined the oil. still i don't care, great price.

Project is not going to happen for quite a while, realized i need more building experience.

first stage condenser will problably change to a chilly1 big blue.

regards

k.us]http://img296.imageshack.us/img296/2406/dscn2164rk1.jpg[/URL]
[URL=http://g.imagesh

I've been wondering about those compressors too, at that price it may be worth to pick up a few.