why would the suction gas from the evap be any warmer then the evap itself? That's kind off impossible unless your insulation is insufficient.
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why would the suction gas from the evap be any warmer then the evap itself? That's kind off impossible unless your insulation is insufficient.
The suction gas will of course heat up as it begins its return path through the low pressure circuit, and through each heat exchanger picking up heat along the way. And you are correct in your observation that the only reason for any rise in temperature on the interconnecting line from the evap to the top of the cascade heat exchanger would be due to insulation losses (approximately 10 watts for a typical line).Quote:
Unknown_road stated... why would the suction gas from the evap be any warmer then the evap itself?
And this is all fine and well, but what I am suggesting, and that which has been proven over and over again, is that if we isolate what I call the subcooler heat exchanger from the evap return circuit, and we feed it with a small portion of the condensate that exits (about 20-30%), the subcooler itself will run at a colder temperature then the cascade that preceeds it (due to its isolation). This will subcool the condenstate that runs through the subcooler, and allow any uncondensed gases to either condense, or dissolve more readily into the condensate that is present. End result: we should see colder evap temperatures when this condensate is later expanded.
Now as to whether this will be needed on the suggested system that 404Power has shown, is debatable. I just know that in a system that utilizes Argon as part of its charge, we see a substantial improvement in using a subcooler as I have proposed. With the refrigerants as suggested in 404Powers design, and dependant upon the heat load, the subcooler may not yield much benefit.
Of course the only real proof would be to attach a thermocouple on each end of the subcooler (suction circuit or discharge circuit), and measure the difference. If things work as I say, you should see a colder temperature at the exit side of the subcooler v.s. the inlet side. So feel free to prove me wrong.
well I would agree with you if the system was designed for loads above 1kW or something but for a load of 200watt I would just shorten the cap tube to the evap so you have enough liquid comming out of the evap to cool the subcooler. Makes it a little easier I think.
But I have to admit I'm just talking theoretical because my autocascade still didn't reach below -80*C without load :D but this also has to do with that I only have r290/r507/r170 and r1150.
Probably would have been better wtih r290, r170, r1150. That and you have no auxillary cooling which does help with capacity.Quote:
r290/r507/r170 and r1150.
To say it would only benefit a system loaded to 1000 watts or higher is not really the case. It really has more to do with what refrigerants you are using, and how cold you want to get. Even a small system benefits if you want to go below -100C, and do so with a reasonable mass flow (not running the suction into a vacuum). Polycold's P-75 (3/4hp) and P-100 (1hp) units are equipped with subcoolers, and were intended to run at temperatures in the -130C to -140C range.
I meant I only posses these gasses, not that these gasses are in my autocascadeQuote:
Originally Posted by n00b 0f l337
@mytek: I'm not saying you should use a subcooler, just saying you can also feed the subcooler with liquid that didn't evaporate in the evap
This probably wouldn't buy you anything, since what you suggest makes it sound like the evaporator would be running in a "flooded" state, and therefore would also be at a warmer temperature as a result. In an ideal system you really want to completely expand the refrigerant that is feeding the evaporator, and you want this to occur within the evaporator itself. Expanding gases can generally carry away much more heat, then an unexpanded liquid would. This is what makes a refrigeration system really do its stuff.Quote:
Unknown_road stated... I'm not saying you should use a subcooler, just saying you can also feed the subcooler with liquid that didn't evaporate in the evap
Of course there is also a great possibility that I am simply misunderstanding what it is that you are trying to say :confused:
Anyway, I assure you that when a subcooler is implemented in the way that I previously showed, it will produce a colder liquid to enter the final captube, and do so better then any other method that has been suggested thus far. Of course the best way to prove this is to monitor the temperatures going into and out of the subcooler. If I get a chance, I'll do that very thing on one of the systems I service for a company I contract to.
Mytek, what do you think of using unfloated oil separators as phase separators?
@ n00b:
Look here! :) (one of cryo-tek's old "bad projects" - pics! ^^)
Looks like a Temprite 340 there I think! ^^
http://www.xtremesystems.org/forums/...7&d=1145658788
lol offcourse refrigerant is boiling in the evap but since we use very small evap's it very easy to flood them, no vaporisation means the evap is already colder then the boiling point which means the refrigerant doesn't boil off anyway no matter how much is in the evap.Quote:
Originally Posted by mytekcontrols
since the mass flow to the evap isn't much you also don't need that much refrigerant for the subcooler.
Thats what I thought since they're just baffled, plus I got a large box of em.
IIRC, those may not be 340's....they're actually custom made for him from TempriteQuote:
Originally Posted by 404Power
Well they seem to be about the same size as 340's, they have the same input, output, oil spots as temprite 340's, they're clearly steel, so they would only be different on the inside, but whats the difference? Who knows, 340's are just baffles and such to stop liquid from rising under pressure and collisionary forces. I already think they'd work well as phase seps, but thats sorta just a bit of confirmation.
I agree with you n00b! ^^ :)
I'll also use them as phaseseps I think ... can't think of any better solution! ^^
Surely oil seps are much more expensive to use as phase seperators than some copper pipe with a bit of wool inside? Empty MAPP gas bottles would probably be cheaper still for those who use it for brazing. Luke uses the MAPP bottles :).
Luke doesnt have temprites at $5 a pop ;)
Any suggestions on autocascade charging. Im going to pull my hair out soon lol.
The spec of the machine is as follows:
1HP rotary
R290/R23
HX is about 4 metres tube in tube
phase sep is a modified old accumulator about 1 litre capacity
captubes on both stages, 2.5m on evap and 2.5m on hx
I have no idea what pressures I should be running at high and low, also I have no idea how to go about charging it. My main problem is not getting the HX cold, I seem to be getting R290 temps on the evap, obviously the R23 is not condensing and somehowthe propane is making its way to the evap.
Im not sure but this seems weird, either the propane is not condensing (which I doubt) or it seems like the high stage captube is blocked somehow.
What do you guys think?
Check captubes first :)
It seems like blocked R290 captube for me...
Blocked captube makes sense, but if it was, the r290 would be having to build up to the top of the seperator wouldn't it?
True, but maybe he overcharged with R290 (although 1 liter is a pretty a big charge).
Nope, the pressure would force towards the unblocked.
Even if there was wool inside the seperator?
Yes.
Johann, as I said on MSN, try to add more R290 and more R23. You must have both gases inside system to have subzero HX temp.
Definitly!
With autocascades you should expect positive low side pressures, this will result in an evaporator temperature lower then that of the bp (@ 0 bar) of your final gas. With r23 you might expect around a -60C load in a good system? This begins to show its beauty when you have r14 or the like and we can get the -100C we strive for in 2 stagers.
Johann, doesn't the HX get cold at all or only a few degrees below room temperature?Quote:
Originally Posted by n00b 0f l337