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With that temperature on the second stage i'm guessing that you've sized the second stage for pretty high capacity?
to be honest it was a shot in the dark 2.6m of 0.031 as i have not had much luck with captube and hx before i went for a length i have used before
also i think LD and clod_ice have used this length with there plated hx
and as i have never worked with r1150 before i dont no what kind of a hit the 2nd stage hx will take
Quote:
Originally Posted by LukeXE
yes r23 on the 2nd
i will try both:)
Good luck baz :D. When are you getting the 2nd case to mount on top?
i have it now but i need the cascade for saturday so it will have to wait nowQuote:
Originally Posted by Brettbeck
That's quiet an impressive looking toy bazx, nice :)
A masterpiece :toast:
been trying to tune the unit but have had a few problems
some how some oil got passed the danfoss oil sep on the 2nd stage
this lead to strip down of the unit
i have swaped out the second stage compressor and replaced it as i was not happy with it,cleaned out the oil cap tube re done some of the pipe work
just got the unit up and running again and am now trying to tune it again
this is much more difficalt then i thought
every time you make an adjustment at the r1150 there is a knock on with all the other comp and hx temps
i have been getting some nice temps tho 1st -38/2nd -80-/evap -102
i am going to shorten the evap cap a bit tomorrow
bazx do you use a section of capillary line on the return feed after the oil seperators? have seen cascades not run well when float opens.
Quote:
Originally Posted by kayl
i use 1/4 copper return too the service port
do you think cap would be better?
i just dont now how the oil got past the sep but it is a worry
i might change it for the temprite same as 3rd stage dont have any problems with that unit
i must say i am enjoying the challenge of 3 gasses it might take me 2 months
to get the hang of this:D
Quote:
Originally Posted by bazx
its worth a try, so dont loose too much suciton that way when open. i just used a few foot.
1st stage would be the hardest to tune i would imagine to tune
http://www.benchtec.co.uk/1/cascade4/1/3/DSC00469.jpg
half way through 06 with a QX6700 @4.2 vcore 1.7 for load all 4 cores with single 8800gtx on air the second stage hx had collapsed to -20
http://www.benchtec.co.uk/1/cascade4/1/3/100.jpg
http://www.benchtec.co.uk/1/cascade4/1/3/DSC00471.jpg
if you look at the DT200 on the left you can see the 3rd stage hx was up and down like a yoyo
this is the R23 stage and oil is getting in the cap tube but i am happy that i am just one oil sep away from a usable cascade
all the above temps were with the evap hooked up to a qx6700 running in the bios or windows
@kayl i would try it if the sep were a lil easyer to get too but as it is such a job to get in there i will just change the sep now
Nice baz :), hope you get it all sorted.
Are you sure? So it was condensing R1150 at only -20c?!Quote:
half way through 06 with a QX6700 @4.2 vcore 1.7 for load all 4 cores with single 8800gtx on air the second stage hx had collapsed to -20
Quote:
Originally Posted by Brettbeck
the thing with plate hx is you can only measure the temp at the suction return
or at the line in
that temp is at the suction return just as the refrigerant leaves the hx
so it will be colder in side the hx but not for long
great 3stage bazx , good luck wit the benching there m8 :)
Wow, nice work
your gonna have some fun with that :D
Is your second stage still cap tube? If so, how is your oil seperator holding up? I could see if enough oil got through it clogging the second stage and starving the 2nd-3rd stage HX. Cyclic refrigerant operation happens for other reasons too such as improper charging and sometimes more subtle roots. Hopefully it's easy to fix like the problem with cascade 3.Quote:
Originally Posted by bazx
Right, going to go over this for you, and anyone else who's listening as well.
Comparing performance of a linear HX and a parallel HX can ONLY be done via the outlet temp of the liquid, NOT the outlet temp of the HX's cooling stage.
If you look at the outlet temp of the cooling refrigerant (high stage) in a linear HX (such as tube in tube) you can use a similar formula to an evaporator to determine the oulet temp of the liquid being condensed. For example, if you have -35c as the outlet of the boiling refrigerant, you may have approx. -20 condensed liquid yeah?
Well in a plate HX or 'series' HX you have as many independant HX's as you have plate areas.
That is, if you have a 20 plate exchanger, you have 10 HX's.
So measuring the output of the high stage refrigerant boiling off is meaningless. It's entirely possible that you'll be colder on the liquid outlet than your returning gas.
So, you MUST measure the liquid of the HX outlet to determine both efficiency, pressure, and load response.
This makes a PT chart that much more important, as you need to be sure that the high pressure refrigerant, especially R1150, is condensing at the temp. and pressure you're targeting.
For Ethylene, you'll have 255psi (approx) at -20.
Is that so bad for a load pressure?
Not really, but anything you can improve on that is great.
Do you have -20 liquid Ethylene temp?
You don't know, because the HX gas outlet and the liquid outlet have NOTHING to do with each other in a series HX that is not fully flooded.
And to be honest, you DON'T NEED a full flood of refrigerant in a plate exchanger, and sometimes you don't want one either.
A plate exchanger is VASTLY more efficient than any coax/tube in tube setup. It can do more in the first couple inches than most tube in tube setups can do in their whole surface area.
So measure the liquid outlet, monitor THAT for the load response and capacity of the high stage, and you will know for sure where you stand.
If the liquid temp continues to increase, sure you need to change the capacity of the high stage.
If the liquid temp goes to say, -20, but remains there under high load, and you're happy with 250 or so PSI as your final stage's load pressure (and that cpu is a HIGH load cpu, as you probably know) then you need to change nothing.
I've got my 2 stage cascade nearly done with a 14 plate HX and I went through the SAME thing, wondering why I couldn't get a full flood without overcharging with captube.
When I started to monitor the liquid outlet I realised that I didn't need one.
So yeah, Hopefully I made sense there, but as more people are using Plate HX's it would be nice for them to know that a slightly different way of thinking about, and approaching it, is necessary as they behave in a slightly different manner to the HX's that most have been using for so long.
Cheers
Gray
hi gray i have just pulled out the hx on the 3rd stage and it is full of oil
what do you think will cause my 12 plate hx to be full of oil
Dam, that is a pain, and something I've been finding myself.
I was thinking it may be the Danfoss oilsep's I've been using, but I think that the more likely cause is either the oilsep is having low temp issues with 'sticking', the oilsep could have failed completely (not that likely unless it was used and not new) and the most likely problem? Too small.
If the oilsep can't quite keep up with the oil flow, and in larger systems you CAN get a high rate of flow, then a larger oilsep designed to keep up with a high rate of flow is needed.
This is part of why the 'home made' oilseps can work really well. They're made incredibly large compared to the manufactured units. They can store huge amounts of oil and in some cases tend to separate better.
I'd say to check the operating temp of the oilsep first, to ensure the oil isn't either too hot or too cold to function as intended within the oilsep.
Checking for a completely 'stuck' oilsep is quite easy.
If your HX is filling though, it may also be an oil incompatibility problem but with ethylene it really shouldn't be. It drags oil around quite well.
It could also be an issue with too much oil in the system.
Compressors are overfilled when new. This is to allow for system size. The oil moves, so they allow for more than is needed to compensate for that, and normally our systems are WAY smaller than the size of the systems that compressors are really intended for.
I would be inclined (and have done so before) to dump the oil from the HX and put it back. That should get rid of the 'overflow' oil and still have enough for proper lubrication of the compressor itself.
A compressor will 'throw' FAR less oil around when it's not filled right up.
Otherwise, what oilseps are you using again? Size, and codes?
There is a chance you'll need to use larger ones to keep up with the oil flow but I think that the biggest problem is a small system with a large amount of oil, and if you remove some of the oil (not too much that you starve the compressor) then the oilseps will likely function in a way that keeps the oil out of the system.
There is ONE thing I would recommend though.
I've been switching to AB oil in all of my cascade Low Stages recently, and it's been saving me a lot of grief.
I have Fuchs AB synthetic, which is guaranteed miscible to -70, and they state that it's quite likely to work fine even lower in temp.
This can mean that on initial startup, most if not all oil will 'cycle out' before low temps can freeze it.
I've been having a lot less hassle on the 2 prototypes I've been working on (very little, but I'm almost done the 'customer stuff' so will be returning to the fun stuff very soon :D) due to this oil in the Low stages.
I've been using it exclusively in systems that require an oil change and it's been remarkable. I've seen a couple of degrees colder due to the oil flowing far better.
As far as oil level goes though, the NL11F is a good example.
It comes with 330ml new (roughly)
If you drain off to about 250ml and then install into a new system, you'll get far less oil issues even in a single stage, because the system is so small you don't need the 'extra' as you don't see nearly as much pipework in our systems as you do in a large Airco unit.
So yeah, I would try that first, lower your oil levels in both Low stages. You may find that cures a lot of oil problems as the 'flow' of oil will be reduced, so the oilsep's won't be fighting the oil nearly as much.
If you get oil issues regardless of your oilsep, switch to a low temp AB synthetic (it tends to be quite compatible with other oils as well) and the small amount that makes it past the oilseps will tend to make it through because it doesn't freeze nearly as badly.
Cheers
Gray
you may well be right about the amount of oil in a small system and the oil you mention sounds like a good idea
Danfoss OUB1 oilsperator is used on the 2nd stage and this is the one that is letting oil past and is well within its operating range
the good thing is i am use the oil sep from cascade 2 in the 3rd stage (1150)Temprite 900 series and it is working very well
but there are differances in there set up the danfoss did not require a pre fill of oil where as the temprite did
also the the temprite is a big sep (4 inch dia) which would fit in with your earlyer comment
so i am now going to get another temprite to replace the danfoss
good work bazx, one thing i'v thinked as 1 start thinking on my 3stager is an oil return cap on 3rd stage hx!, i open that valve betwen cascade working times, when i start 2nd stage or so, before hx becomes cold just becouse some oil that was not catched by separator needs to climb all the hx @extreme temps.
1st stage and 3rd stage have the gravity help
oil is the main fight with the 3 stage
i was talking to esdee and he surgested i use bigger dia cap tube on the 3rd stage hx
now i have 2.6m of 0.031
but i might try 0.042 what do you think
i may also fit a cap return as well for any oil that gets in the hx as it is a pain to remove once unit is compleat