Hey FUGGER for the last few weeks I have been unable to access my user account by clicking my name on the top right of the page or view anyone's user page, so I can't check my PM box or send messages. I thought it might be a bug that would be worked out eventually, but that doesn't seem to be the case. I would have messaged you, but I couldn't, so I figured I would ask you here since you posted in this thread. Thanks for any help.
I am also not able to access my and others pages. Figured it would be due to my low post count. If that's not the case +1 on the problem.Originally Posted by aenigma
Thanks, that makes sense regarding n2o only being an oxidizer at high temps. Good to know it doesn't make a mess of the system at normal/cold temps.
Regarding ethylene, $600 seems expensive for what it is. Turns out the cyl I have isn't empty (80cf cyl currently showing 900psi), but now concerned about running out before I get something really working well. That would be depressing getting something almost working and then running out. The cyl here was given to me from long ago, but if it goes empty I would have to buy more. According to the Airgas catalog the part number for an 80cf of plant growth regulator (PGR grade) ethylene is "EY PGR80". Their definition of PGR grade is 98.5% pure and I'm guessing should be less expensive than CP or UHP grade. I'll try to get a quote before I get too far into it. Maybe what I have is enough though... I don't have a good sense of how much volume/weight is normally needed for a given size compressor.
Another point I'm concerned about is that the critical temperature for ethylene is well below room temp. So, while unplugged from wall power the system would equalize and go supercritical with no liquid (in the normal sense) being stored in a receiver/accumulator at vapor pressure. I'm sure there's ways to deal with it, as it would seem that also applies to systems that use co2 as a refrigerant, but I'll need to look into it further.
Nice, 98.5% should be fine to use as a refrigerant, my automotive nitrous is probably less pure than that since it is mixed with sulfur dioxide and probably has air and who knows what else in it. I would be very interested to know how much that PGR grade ethylene is. I was quoted a price for 'pure' ethylene. Nearly half the price was the shipping though. About $300 for shipping.
If you have 900psi you should have enough to work with, especially if you recover your refrigerant from the autocascade if you have to work on it to change cap tube lengths for example. The critical temperature for many low temp refrigerants is close to room temperature, that is normal. Nitrous oxide has a critical temperature and pressure of 36c at about 1060psi. That isn't an issue with a cascade or autocascade, especially if you have an expansion/buffer tank.
My first autocascade has a low side buffer tank and a hot gas bypass solenoid that will automatically open if head pressure rises above 300psi on startup. My latest autocascade I made out of junk laying around doesn't have a low side buffer tank and it is fine. It has a receiver which I turned into a phase separator and a suction accumulator as a secondary phase separator since I had it lying around and it adds a good bit of volume to the system. Static/base pressure is generally around 150psi, not too bad. Sometimes the compressor groans when starting, but it was made in 1989 and pretty weak. I added an old rotary compressor to make it a 2 stage to help it out. Just to clarify what I mean by 2 stage is that the original compressors discharge line enters the suction line of the rotary compressor, thereby reducing the compression ratio.
In the transcritical co2 systems the company I work at manufactures the compressor is started when the pressure in the receiver has risen. Although it is possible to make a system or a vessel that could support the room temperature pressure of the gas.
If you make a vessel that can withstand the pressure and you can pump down all the liquid and store it, then the system can be designed for a lower pressure. I have no experience in this. though I think it's possible.
@aenigma
Sulfur dioxide doesn't sound very nice. if it's acidic maybe you can purge it with a burn-out filter.
Or what I read on a forum is bubbling it through water seems to remove the sulfur dioxide, since it binds to water. Water is also not desirable but maybe better than the So2. if you can suck it through a filter drier into the system. Just an idea..
It is used as a refrigerant. hmm
Last edited by Raziel; 10-07-2016 at 05:04 AM.
I'm not completely understanding the idea but any more details would be greatly appreciated.
@aenigma
As far as I'm aware you shouldn't have to pay shipping if you're willing to wait long enough. I have no association with Airgas other than work purchases, but based on that the area rep should be able to get one sent at no cost to one of their regular stops assuming the rep can find a cyl with the right part number to shuffle around. At work we get direct shipments of the regular stuff (nitrogen, oxygen, argon, etc), but a normal stop would also be a local welding shop.
By "pure" I'm guessing they quoted CP grade (chemically pure).
That's very interesting you have a static offline pressure of 150psi. That would mean your system has enough refrigerant to operate but isn't completely 'saturated' (I'm sure there's a more correct term). If you were to keep pumping n2o into it, it should saturate at around 700psi and then some of it would turn to liquid at some place within the system. That wouldn't happen with ethylene at room temp. I can see the advantage of having a buffer tank so that a minor +/- in refrigerant charge doesn't make as much of a difference and makes the whole system less sensitive to a slight over/undercharge.
Thinking about it some more, are you referring to a self-regulating system where a surplus of extra refrigerant is stored in a high pressure container and an over-charge situation automatically pumps refrigerant from the system into the container, and an undercharge situation automatically releases some refrigerant into the system?
Yeah like that. Extract the surplus to keep the pressure low in the system. store it in the high pressure vessel and block it off with stop valves or solenoid valves.
Like when you pump down a normal refrigeration system by closing the receiver exit valve and bypass the low pressure safety switch.
Yeah I believe it was 99.5% purity and chemical grade, it was a specialty gas so it would be drop shipped to me. I just got the quote by e-mailing them. Even without shipping it would be too much money to be worth it.
In an autocascade or cascade you need much less high pressure gas than you might think. If you start off by base charging the high pressure gas first when it is vacuumed you will only get about 25-50psi with a system that has quite a bit of volume. If static pressure was 700psi it would be wayyyyy overcharged. If I add any more my running high side pressure would just rise and increase the compression ratio eventually raising the evap temperature. A little goes a long way. The buffer tank is only used to keep static and startup pressures safe, it doesn't really make much of a difference when charging. Startup high side pressures before the high pressure starts condensing can easily get over 400psi without adequate storage volume which isn't good for the compressor.
My static pressure today was only 125psi since it is only 57f in the shop. Earlier in the heat of the summer when it was 90-100f in the shop it was around 200 I believe.
<edit> I forgot to mention it only has 100pm sulfur dioxide so it's not that big of a deal, it's the non-condensables such as air that it may have in it that I don't like. I don't know if it has much, but being automotive grade I wouldn't be surprised. Yup, sulfur dioxide used to be used as a refrigerant long ago, it's not a big deal at such low concentrations. They only add it so people don't huff it to get high. Also I think the reason my static pressure was only 125psi this morning is because my rotolock receiver valve must have started leaking again overnight as it was undercharged. Such is the way of the road when using old junk haha.
Last edited by aenigma; 10-07-2016 at 11:10 AM. Reason: Forgot to mention the sulfur dioxide.
couldn't you buy a 2 stage lab freezer ie. Cold trap with r1150 in it and extract the gas? last saturday I went to a refrigeration scrapyard to look around for interesting stuff and the guy told me he had some lab freezers a while back with an ethylene filled second stage. too bad he didn't have more units.
Aenigma did you get a quote from linde gas ? I can purchase here. don't know about America. If you want, I could give it a shot.
Last edited by Raziel; 10-10-2016 at 12:57 AM.
Yeah that would work, but I don't know of anywhere around here that would have anything like that. I live in a pretty small town. I didn't get a quote from linde but I am sure it would be expensive too. Ethylene is pricey stuff.
I checked at work just hypothetically if it were a work assignment (not just self educational), and it turned out to be affordable. All they had on file is a CP grade 300CF cyl but it was reasonable for even that, and I have to assume a PGR grade 80CF cyl should be even quite a bit less. I still need to call a local weld shop on my own to see what it would actually cost me personally as opposed to being a work assignment. They have a zip code dealer finder on their website.
Not sure if I'm following this. Not contesting, just not seeing the full picture I guess. Specifically not exactly following where the 25-50psi limit would come into play. I'm picturing a static system being charged to a static pressure then powered up to see if it all works as calculated. Seems the system should take as much refrigerant as you would like to insert into it until the inserted gas either liquefies somewhere in the system or makes the system pop a leak. Again not contesting, just trying to understand the bigger picture.
Ah, sorry. It is not a limit, I was just saying for a system with an ideal amount of volume; such as receivers, accumulators and/or expansion tanks, it only takes 25-50psi of the n2o when added after a vacuum. It really depends on the total system volume of course. If you have enough volume it could be only 15psi and if you have no volume it may be almost 100psi. My point was you will never have hundreds of pounds of pressure from a 2nd stage static/base charge in a system.
You could charge the 1st stage refrigerant then add the 2nd stage refrigerant until it is working properly and shut it off, let it equalize and warm up then check static pressures and they still wouldn't be that much higher than the sst/sct of the high temperature refrigerant.
My skype is Vibrophil if you want me to explain this further.
Thanks for the clarification, that makes sense.
My imaginary concern was that the system needs to drop down below the critical temp before the low temp refrigerant even becomes useful. At that point the system needs a certain amount of liquid/vapor refrigerant for the low temp section to function correctly. Once the system is unplugged from wall power that same amount of liquid has nowhere to go other than to turn back into very high pressure gas (which is different than n2o where it could max out at ~700 psi without popping the system and stay in the system partially as a liquid).
Sounds like I'm imagining way too large of a charge though and your clarification again makes sense. Thanks. Everything I've played with up to this point has had max pressures under 400psi or so, but again this is a learning experiment/challenge for me more than anything else. Just an experiment to see if I understand the math and see how far I can stretch it via the cascade/autocascade process without involving any other processes.
One of the systems at work requires about 45lbs of liquid r22 refrigerant for a 5 ton compressor. Liebert calls it "lee-temp" in order to make sure the system still functions correctly during the cold winter months, still needing A/C indoors with ambient outdoor condenser temps well below zero C. There's no way that 45lbs of liquid r22 would stay anywhere within the system without popping it if the critical temperature and vapor pressure at outdoor summer temps and static offline pressures didn't line up with allowing it to remain mostly a liquid.
Wow 45lbs, that would be an expensive unit to fill haha. I am guessing it also uses a head pressure fan controller so the condenser fans only operate when needed.
These autocascade are much smaller, we are only talking about ounces of refrigerant and an autocascade always takes more 1st stage gas than the lower stage gasses. When the system is off then the low temp refrigerants will turn back into vapor and just increase the base static pressure of the liquid 1st stage refrigerant. This is why you want the expansion tank depending on how much low stage refrigerant(s) you add. Especially when it is more than 2 stages.
On my autocascade if I close the 2nd stage discharge line valve the head pressure can get up over 300psi since it isn't condensing the nitrous, just compressing it and storing it in the receiver without entering the interstage heat exchanger. When I have it running normally, like I do right now, high side pressure is only 195psi and my evap is -102c, but it is very cool in the shop at about 14c.
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