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Post by Travis on Aug 30, 2020 15:39:12 GMT
You can buy SO2, but it’s very expensive. The last time I priced it, it was $700 for a 30 lb cylinder plus cylinder rental. The cost, the difficulty of getting it and the issues of having a leak is why everyone here searched for an alternative.
It’s also next to impossible to rewind a motor using materials that are compatible with SO2 in today’s world. I’m unaware of a source of real cotton insulated wire.
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Post by ChrisJ on Aug 30, 2020 21:27:17 GMT
You can buy SO2, but it’s very expensive. The last time I priced it, it was $700 for a 30 lb cylinder plus cylinder rental. The cost, the difficulty of getting it and the issues of having a leak is why everyone here searched for an alternative. It’s also next to impossible to rewind a motor using materials that are compatible with SO2 in today’s world. I’m unaware of a source of real cotton insulated wire. PTFE windings are compatible no? |
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Post by turbokinetic on Aug 30, 2020 22:52:47 GMT
Your reply has escaped my notice until now. Thanks. I guess I have not yet learned how to navigate on these forums. I have no access to r227, and based on my figures I don't want to be the guinea pig. One would need 24 degrees F of superheat at the compressor inlet to keep from dumping liquid refrigerant into the dome, so I don't want to try this. I brought up the topic because I know that some people are using it for an SO2 replacement in monitor tops. I even saw a You-tube video of someone doing this. My figures raised some alarm bells, and I was wondering if my thinking is wrong. If not, then anyone considering r227 should be warned. Aren't you the same guy who does videos on replacing SO2 in monitor tops with r152a? I learned a lot from these videos, and r152a is also one of my refrigerants of choice. However, Coldspaces here has had mixed results with his experiments with r152a. Have you seen his posts? Have you had trouble with rattling or stuck float valves? I'd really rather use the factory recommended refrigerant, if I can get it anywhere. I would probably keep the refrigerator on the porch anyway, so I'm not so worried about a sulfur dioxide leak. Perry Hahn Hi Perry. You're correct; I'm the one who has done several videos on using R152A in monitor tops and other fridges. When it comes to the float valve, there have been some issues. The liquid phase of R152A is about 1/3 less dense than that of SO2. This means the float chamber has to operate at a higher level to reach the same level of float lift. As a result, there is less room above the float for noncondensable gases to collect before they impair the float operation. It's been my experience that the CK machines (where the compressor discharge goes "directly" through the condenser to the float) do not have any trouble with R152A. The DR machines (where the compressor housing provides a large volume in the high side, between the compressor outlet and condenser) are very sensitive to NCG in the system. GE even mentions this in the manual as a possibility. With the lower density of the R152A, this becomes even more important. I've charged 2 DR's successfully with R152A. Both of them required several NCG purges from the top of the float chamber right after charging, and for the first few operating hours. After that had been done, they have been operating successfully. Gill and I have talked about his R152A experiments. He can add more I'm sure; but IIRC; at the time he needed to get the units going and had a heavier refrigerant, R124, available and used it instead of spending more time with R152A. The reason I prefer to avoid R124 is due to its being a phase-out refrigerant. I take exception to politicians getting involved in engineering; and the resulting taxation and money game it leads to. For that reason I would prefer to avoid phase-out refrigerants unless there is nothing else suitable. Again this is purely my feelings on the situation and I don't have bad feelings about anyone else choosing any other refrigerant. I've been testing R1234ZE in the older R114 Frigidaires as well. That is a new HFO gas that's a little hard to get in the States, but it will probably become more available in the future. There are 3 units using it as far as I know; with all of them performing very well. It has a pressure/temperature chart in between SO2 and R152A. I would love to see the R277 experiments! Could you please post a link to the videos? You can buy SO2, but it’s very expensive. The last time I priced it, it was $700 for a 30 lb cylinder plus cylinder rental. The cost, the difficulty of getting it and the issues of having a leak is why everyone here searched for an alternative. It’s also next to impossible to rewind a motor using materials that are compatible with SO2 in today’s world. I’m unaware of a source of real cotton insulated wire. PTFE windings are compatible no? I know that one rebuilt unit with PTFE windings had a failure with SO2. it appeared to be the slot liner (ground wall) insulation which deteriorated, and allowed the winding to touch the iron laminations and ground fault. I have doubts that the slot liners were PTFE based on how they deteriorated. There is just not much reason to stay with SO2, now that we have much safer, less costly, and less harmful refrigerants available. The engineers built these machines around the properties of SO2 because it was easily manufactured and was almost the only low-pressure refrigerant they had in the early days. Unless pure nostalgia is why you want to recahrge with SO2, there isn't any real benefit. But if you want it for nostalgic reasons, that is very cool and I would love to see how it goes, obtaining it and adapting the tanks etc. Sincerely, David |
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Post by ChrisJ on Aug 31, 2020 0:37:04 GMT
I'm confused as to why you had NCG with 152 if you pulled a good vacuum down to 250 microns or less?
How did NCG get in the system?
I'd be happy with any gas as long as it performed as well as SO2 in the system.
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Post by turbokinetic on Aug 31, 2020 3:48:14 GMT
I'm confused as to why you had NCG with 152 if you pulled a good vacuum down to 250 microns or less? How did NCG get in the system? I'd be happy with any gas as long as it performed as well as SO2 in the system. Hi Chris. There are a number of ways NCG could be in the system. I have a theory that there are void spaces in the compressor which may trap air and release it once the compressor is operated. Alternatively, there could have been a leak on my gauges, or an error when I punctured the cans and allowed air in; or there could have been air in the can from the factory. I doubt the air from factory theory because the same cans are used on all my projects and this issue has been unique to the DR's only. I'm with you as well, not partial to any gas as long as it works! I'm all about trying new things which may open up more possibilities. Sincerely, David |
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Post by Travis on Aug 31, 2020 15:00:59 GMT
Chris J,
The PTFE wire was very expensive and doubled the cost of the stator rewind. I’m sure someone could rebuild and use SO2, but it seems unnecessarily expensive and complicated.
I suspect David is correct that NCGs come from compressor voids, leaks in the can tap and possibly in production. It’s not like they’re intending this type of canned air to be used as refrigerant.
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Post by perryhahn on Sept 1, 2020 15:07:18 GMT
Your reply has escaped my notice until now. Thanks. I guess I have not yet learned how to navigate on these forums. I have no access to r227, and based on my figures I don't want to be the guinea pig. One would need 24 degrees F of superheat at the compressor inlet to keep from dumping liquid refrigerant into the dome, so I don't want to try this. I brought up the topic because I know that some people are using it for an SO2 replacement in monitor tops. I even saw a You-tube video of someone doing this. My figures raised some alarm bells, and I was wondering if my thinking is wrong. If not, then anyone considering r227 should be warned. Aren't you the same guy who does videos on replacing SO2 in monitor tops with r152a? I learned a lot from these videos, and r152a is also one of my refrigerants of choice. However, Coldspaces here has had mixed results with his experiments with r152a. Have you seen his posts? Have you had trouble with rattling or stuck float valves? I'd really rather use the factory recommended refrigerant, if I can get it anywhere. I would probably keep the refrigerator on the porch anyway, so I'm not so worried about a sulfur dioxide leak. Perry Hahn Hi Perry. You're correct; I'm the one who has done several videos on using R152A in monitor tops and other fridges. When it comes to the float valve, there have been some issues. The liquid phase of R152A is about 1/3 less dense than that of SO2. This means the float chamber has to operate at a higher level to reach the same level of float lift. As a result, there is less room above the float for noncondensable gases to collect before they impair the float operation. It's been my experience that the CK machines (where the compressor discharge goes "directly" through the condenser to the float) do not have any trouble with R152A. The DR machines (where the compressor housing provides a large volume in the high side, between the compressor outlet and condenser) are very sensitive to NCG in the system. GE even mentions this in the manual as a possibility. With the lower density of the R152A, this becomes even more important. I've charged 2 DR's successfully with R152A. Both of them required several NCG purges from the top of the float chamber right after charging, and for the first few operating hours. After that had been done, they have been operating successfully. Gill and I have talked about his R152A experiments. He can add more I'm sure; but IIRC; at the time he needed to get the units going and had a heavier refrigerant, R124, available and used it instead of spending more time with R152A. The reason I prefer to avoid R124 is due to its being a phase-out refrigerant. I take exception to politicians getting involved in engineering; and the resulting taxation and money game it leads to. For that reason I would prefer to avoid phase-out refrigerants unless there is nothing else suitable. Again this is purely my feelings on the situation and I don't have bad feelings about anyone else choosing any other refrigerant. I've been testing R1234ZE in the older R114 Frigidaires as well. That is a new HFO gas that's a little hard to get in the States, but it will probably become more available in the future. There are 3 units using it as far as I know; with all of them performing very well. It has a pressure/temperature chart in between SO2 and R152A. I would love to see the R277 experiments! Could you please post a link to the videos? PTFE windings are compatible no? I know that one rebuilt unit with PTFE windings had a failure with SO2. it appeared to be the slot liner (ground wall) insulation which deteriorated, and allowed the winding to touch the iron laminations and ground fault. I have doubts that the slot liners were PTFE based on how they deteriorated. There is just not much reason to stay with SO2, now that we have much safer, less costly, and less harmful refrigerants available. The engineers built these machines around the properties of SO2 because it was easily manufactured and was almost the only low-pressure refrigerant they had in the early days. Unless pure nostalgia is why you want to recahrge with SO2, there isn't any real benefit. But if you want it for nostalgic reasons, that is very cool and I would love to see how it goes, obtaining it and adapting the tanks etc. Sincerely, David |
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Post by perryhahn on Sept 1, 2020 16:29:28 GMT
I guess that I still haven't figured out to navigate in this forum. I managed to reply to a message without posting anything. Last night, I looked for that video about the experiment with r227ea, and I couldn't find it. From my recollection, however, it was not really an experiment. Someone simply repaired a sulfur dioxide monitor top, and filled it with r227ea. There was nothing about how well it worked, but apparently he had been using this refrigerant before. I did find a similar video about someone filling a sulfur dioxide monitor top with propane. Propane has a density of about 500kg/m3, or about a third of the density of liquid sulfur dioxide, so I am highly skeptical that it can lift the float valve, especially since people are having trouble with r152a. Liquid propane is so light that it will float on top of the refrigerant oil. At 100 degrees F, saturated propane has a pressure of 1.3MPa, or two and a half times the saturated pressure of SO2. It is totally miscible with mineral oil, so it will lower the viscosity considerably. Just consider the fire hazard when you have a compressor dome filled with hot propane at pressures close to the test pressure of the dome. I have all kinds of objections to propane, and the fact that people are already using it is not reassuring. We don't know what happened after he turned the camera off. This video can be seen at www.youtube.com/watch?v=a5syN06WjpYOne of the commenters after that video insists that propane will dissolve the varnish in the cotton cloth insulation around the motor windings, eventually causing arcing. I don't know if this is true, but it is quite plausible. It also gives me pause when considering other refrigerants, most of which make excellent solvents. The more important lesson from this is that there are so many things like this that we don't even think about when we make our calculations. In the final analysis, we really won't know if a substitute refrigerant is as reliable as the original SO2 until another 90 years have passed. There is a lot to be said for SO2 as a refrigerant. I have been corresponding with Birkie, and according to his calculations, it still has by far the best COP of the potential substitute refrigerants. There are no unknowns as to its reliability. It runs at a low pressure. It is an excellent refrigerant for a refrigerator that you keep on your screen porch, where there is enough ventilation so that a potential leak is not dangerous. Unlike most of the other refrigerants, there is absolutely no fire hazard. Perry Hahn |
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Post by Travis on Sept 1, 2020 17:07:24 GMT
Perry,
Why would we want to keep our refrigerators on the porch? I’m not saying that SO2 is bad, but the negatives outweigh the positives.
If someone needs to recharge their unit, do we just tell them to buy some SO2. There’s already enough fear about it to advocate for an inexperienced person to use it.
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Post by turbokinetic on Sept 2, 2020 1:43:23 GMT
I guess that I still haven't figured out to navigate in this forum. I managed to reply to a message without posting anything. Last night, I looked for that video about the experiment with r227ea, and I couldn't find it. From my recollection, however, it was not really an experiment. Someone simply repaired a sulfur dioxide monitor top, and filled it with r227ea. There was nothing about how well it worked, but apparently he had been using this refrigerant before. I did find a similar video about someone filling a sulfur dioxide monitor top with propane. Propane has a density of about 500kg/m3, or about a third of the density of liquid sulfur dioxide, so I am highly skeptical that it can lift the float valve, especially since people are having trouble with r152a. Liquid propane is so light that it will float on top of the refrigerant oil. At 100 degrees F, saturated propane has a pressure of 1.3MPa, or two and a half times the saturated pressure of SO2. It is totally miscible with mineral oil, so it will lower the viscosity considerably. Just consider the fire hazard when you have a compressor dome filled with hot propane at pressures close to the test pressure of the dome. I have all kinds of objections to propane, and the fact that people are already using it is not reassuring. We don't know what happened after he turned the camera off. This video can be seen at www.youtube.com/watch?v=a5syN06WjpYOne of the commenters after that video insists that propane will dissolve the varnish in the cotton cloth insulation around the motor windings, eventually causing arcing. I don't know if this is true, but it is quite plausible. It also gives me pause when considering other refrigerants, most of which make excellent solvents. The more important lesson from this is that there are so many things like this that we don't even think about when we make our calculations. In the final analysis, we really won't know if a substitute refrigerant is as reliable as the original SO2 until another 90 years have passed. There is a lot to be said for SO2 as a refrigerant. I have been corresponding with Birkie, and according to his calculations, it still has by far the best COP of the potential substitute refrigerants. There are no unknowns as to its reliability. It runs at a low pressure. It is an excellent refrigerant for a refrigerator that you keep on your screen porch, where there is enough ventilation so that a potential leak is not dangerous. Unlike most of the other refrigerants, there is absolutely no fire hazard. Perry Hahn Hi Perry. It's OK if you couldn't find that video. No hard feelings. The Internet is a strange place where things come and go. I'm guilty of removal of some videos which became controversial or where I was not able to complete the project. The video of the CK with propane is by one of our members. He goes by a different screen name here than his YouTube handle. I think I remember when this was posted. Can't remember if he says so in the video, or if it was in a post here; but the propane charge was a test to see if the unit was viable and worth more work since he obtained it with a broken line. I've been a vocal opponent of HC refrigerants as alternatives for a multitude of reasons. As you mentioned, the pressure/temperature relationship of propane is far and above the design limits of a SO2 or R12 machine. If the unit is shut down and left in a hot place, the vapor pressure will dramatically exceed the test pressure for which the unit was designed. Propane is extremely flammable, in a wide range of concentrations in air. There are people who pop up often advocating this and claiming it works for them, but you never see any longterm success stories. They also sell HC based blends for automotive R12 replacement. Those are known to be a poor choice in flooded evaporator designs, as well. The higher pressure component will boil off first, in the flooded evaporator; "distilling" the material and allowing only the higher pressure part to circulate with its associated elevated condensing pressure. As for the cotton windings, there is no varnish on the magnet wire. The oiled cotton its self is the only insulation. Frigidaire used cotton insulated winding in their first hermetic unit, the early 1930's Meter-Miser. They used R114 with this. The R114 is fully miscible in oil and dissolves most oils and greases. Frigidaire had to go through extra cleaning processes to remove all traces of grease and oil from the parts. Otherwise, the R114 would dissolve them, carry them throughout the system, and clog / contaminate the metering device. I expect propane would have similar effects. A couple years ago, I had a good visit with someone who worked in the industry when these fridges were still in common daily use. We talked at length about refrigerants, oils, and the changing and obsolescence of different gases. When R114 came out, it was touted as an SO2 replacement. The pressure / pressure is similar; but the oil miscibility is very different. He told me how it was about a 50/50 shot of things going south, when a SO2 unit was recharged with R114. The older and dirtier the system, the greater the chance of a failure. The SO2 doesn't really dissolve and carry things around the system. Therefore, they build up as hard deposits. Once a highly solvent-like refrigerant is introduced, much of the deposits are dissolved and circulate, with harmful effects. When rebuilding the old Frigidiare systems, I find they often have very significant deposits in them. I can sure see how that would be a problem if it were suddenly to start circulating! |
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Post by perryhahn on Sept 2, 2020 6:24:21 GMT
Have you tested the r1234ze in the monitor tops as a substitute for SO2? I am interested in that refrigerant because they are phasing out r124. In some ways, r1234ze is much closer to r124 than it is to r152a. Both refrigerants have a high miscibility with mineral oil, whereas mineral oil will only contain about 16% dissolved r152a under compressor dome conditions. Under adiabatic compression, (which, of course, never really happens,) from the saturated vapor state, both refrigerants stay in the saturated state instead of going into superheat. Both are less likely to have float valve issues. I am willing to bet that both of these refrigerants require a bigger sump heater cartridge of unknown wattage. Aaron (Birkie) says that you sometimes use a potentiometer or dimmer switch in series with the heater cartridge, in order to determine the optimum wattage. This might make a good permanent feature, as we may want to have a different heater setting during the winter. I would still rather use SO2 if I can find it. In answer to Travis' question, I can't think of any better place to drink beer than on the front porch or in the car port. Once you go inside into the air conditioning, you aren't nearly as thirsty. It would make an excellent conversation piece there while one is engaging in projects with one's redneck friends, especially if it contains beer. And we all know that some of the best ideas in history have been alcohol inspired. This forum appears to be a rather close knit group, and I may have inadvertently committed a major faux pas by raising my reservations about a video made by one of the members. I have a tendency to think out loud too much. I'm hoping that David is right, and the propane video was just to test the machine with an inexpensive gas. This would make me look like the idiot instead of the fellow who made the video, so that I'm not really stepping on anyone's toes. For the record, though, if anyone wants to trash any of my ideas, don't even hesitate. Birkie can testify that I don't have a fragile ego at all. Getting off of the topic a bit, here is a very, very depressing video. I have so many objections, I don't even know where to start: www.youtube.com/watch?v=Mj276nXttrgPerry Hahn |
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Post by turbokinetic on Sept 2, 2020 7:32:41 GMT
Have you tested the r1234ze in the monitor tops as a substitute for SO2? I am interested in that refrigerant because they are phasing out r124. In some ways, r1234ze is much closer to r124 than it is to r152a. Both refrigerants have a high miscibility with mineral oil, whereas mineral oil will only contain about 16% dissolved r152a under compressor dome conditions. Under adiabatic compression, (which, of course, never really happens,) from the saturated vapor state, both refrigerants stay in the saturated state instead of going into superheat. Both are less likely to have float valve issues. I am willing to bet that both of these refrigerants require a bigger sump heater cartridge of unknown wattage. Aaron (Birkie) says that you sometimes use a potentiometer or dimmer switch in series with the heater cartridge, in order to determine the optimum wattage. This might make a good permanent feature, as we may want to have a different heater setting during the winter. I would still rather use SO2 if I can find it. I haven't, personally, tried anything other than R152A in a Monitor Top with a high-side dome design. I have one DR-D2 with original SO2 charge, and the DR1 with R152A. They are different size machines so it's not an apples-to-apples comparison. The DR1 is quieter and the evaporator gets cold / condenser gets hot quicker than the DR-D2; and the DR1 is quieter. As for the heater, In the DR1, it has a 20W heater; which is what I had on-hand from a group buy. The DR1 has worked very reliably and quietly in cool and hot weather. It's in my non heated and non airconditioned workshop. We also did a DR3 and increased its heater quite a lot. It had a heat increase from 18W factory to 60W; in order to eliminate rattle. Gill has used R124 and also increased the heater to (if I remember) 40W to get a quiet operating machine. The heater choice in my case was based upon what I had on hand. I did first ramp up the wattage using a Variac, and it seemed that between 40 and 50W all rattle disappeared. The only heater value I had close to that for permanent installation was a 60W. I do plan to try R1234ZE in a monitor top. I'm curious where you were able to get detailed info about R1234ZE oil miscibility. Honeywell does say it is "more soluble" in mineral oil than HFC and gases, but they don't say by how much. I may have said already but the R1234ZE is working well in at least 3 Frigidaire hermetic units, which have high side dome configuration. They don't have float valves, though. The Frigidaire which got the R1234ZE was one I had already majorly worked on and it was not someone else's property I was taking a risk with. I had already cut open and rewelded the compressor once, and we have pictures of how it looked. So if it fails, we can compare and see if any strange wear or corrosion happened. That one has continued to work without issue; and two more have had this gas used in them since that. As for my DR1; it got R152A because at that time I was out of the R1234ZE; and it presented an opportunity to learn. There had been so much discussion of R152A not working in DR's that I wanted to get to the bottom of why others had been unsuccessful. Next one I'll try the R1234ZE. This thread is so long now I can't remember if I posted it or not. Did you see the R1234ZE video, in the Frigidaire? Your comments on the propane video were made out of legitimate concern, very understandable without the context of what was going on. No harm no foul! I feel as if this is a pretty close-knit group. Several of us are in-real-life friends as well as Internet friends. One of the good things about the forum is the differing ideas we share. We have people from all different professions here, with knowledge shared from different angles. Many people come here for advice and are helped, because that gives satisfaction. There are fewer who come to discuss the science and materials behind our hobby; as you have. That is good for all of us! The R1234ZE idea was not originally mine; but I was possibly the first to locate a supplier of it in small cans and actually charge a vintage unit with it. Someone was talking on an automotive forum about the new automotive R1234YF and the different isomers were mentioned. That got me looking into it and found the data sheet on the Solstice ZE product. The Solstice ZE is not yet officially approved in the trade circles in the States; so it is not easy to get in larger containers; unless you special order it and pay accordingly. I was able to track down a company who sells it in cans, for a medical / electronics freeze spray. It's not cheap that way but it is at least possible to get it. Look up MG Chemicals Super Cold 403C if you need it. Awe yeah! I saw that! There is some discussion of it elsewhere, and I think it was discovered that the utility company has it on display now. Or at least they did when it was last discussed. I always hate to hear about those buy-back programs. It pisses me off only slightly less than the cash-for-clunkers fiasco. |
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Post by joneske on Sept 2, 2020 17:13:44 GMT
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Post by perryhahn on Sept 3, 2020 4:06:20 GMT
I got the miscibility data for r1234ze with mineral oil from pdfs.semanticscholar.org/aa77/26b6a8118546b6f3f23f67d7b66018c57bd4.pdfI got the miscibility for most of the other potential SO2 replacements in mineral oil from www.ahrinet.org/App_Content/ahri/files/RESEARCH/Technical%20Results/MCLR-Program/Miscibility%20of%20Lubricants%20with%20Refrigerants-Pate-Zoz-and%20Berkenbosch-1993-DOE-CE-23810-18.pdfFinally Aaron (Birkie) showed me relevant miscibility data for SO2 from the reference section for this forum. That was the first time I had seen any miscibility data for SO2, and it was an eye opener for me. Until then, I had been under the impression that SO2 was practically immiscible in mineral oil. I knew that just a little bit of dissolved refrigerant lowers the viscosity of oil by quite a bit, so I thought that it was necessary to find another refrigerant with very low miscibility in order to achieve the oil viscosity for which the machine was designed. As it turned out, there is quite a bit of dissolved SO2 in the oil, and the good engineers at GE no doubt took that into account when they designed journal bearing tolerances and selected the oil used. Birkie totally trashed all of my ideas about this, and I'm happy that he did. Ranking refrigerants by miscibility in mineral oil, from least to most, we get r132a, r152a, SO2, r124, and finally r1234ze. However, under the running conditions of the compressor dome in a monitor top, my data says that both r124 and r1234ze should be totally miscible in the oil. Birkie has another source which indicates a definite limit in the level of miscibility for r124 under those conditions. There are a number of types of mineral oil that will give different test results for the various refrigerants. Do we know exactly what kind of mineral oil is in the monitor tops? Perry Hahn |
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Post by turbokinetic on Sept 3, 2020 4:22:44 GMT
I got the miscibility data for r1234ze with mineral oil from pdfs.semanticscholar.org/aa77/26b6a8118546b6f3f23f67d7b66018c57bd4.pdfI got the miscibility for most of the other potential SO2 replacements in mineral oil from www.ahrinet.org/App_Content/ahri/files/RESEARCH/Technical%20Results/MCLR-Program/Miscibility%20of%20Lubricants%20with%20Refrigerants-Pate-Zoz-and%20Berkenbosch-1993-DOE-CE-23810-18.pdfFinally Aaron (Birkie) showed me relevant miscibility data for SO2 from the reference section for this forum. That was the first time I had seen any miscibility data for SO2, and it was an eye opener for me. Until then, I had been under the impression that SO2 was practically immiscible in mineral oil. I knew that just a little bit of dissolved refrigerant lowers the viscosity of oil by quite a bit, so I thought that it was necessary to find another refrigerant with very low miscibility in order to achieve the oil viscosity for which the machine was designed. As it turned out, there is quite a bit of dissolved SO2 in the oil, and the good engineers at GE no doubt took that into account when they designed journal bearing tolerances and selected the oil used. Birkie totally trashed all of my ideas about this, and I'm happy that he did. Ranking refrigerants by miscibility in mineral oil, from least to most, we get r132a, r152a, SO2, r124, and finally r1234ze. However, under the running conditions of the compressor dome in a monitor top, my data says that both r124 and r1234ze should be totally miscible in the oil. Birkie has another source which indicates a definite limit in the level of miscibility for r124 under those conditions. There are a number of types of mineral oil that will give different test results for the various refrigerants. Do we know exactly what kind of mineral oil is in the monitor tops? Perry Hahn Thanks for the links! Yes, Aaron and I have also previously talked about the miscibility. Frigidaire took advantage of the change in SO2 miscibility based on temperature, to allow for their low-side-float oil return system to work! I think we generally have found out that GE considered the oil to be their "secret sauce" and they didn't really let out the formula, although some have figured out the basics. One thing to remember about in-sump oil dilution is that there are two designs at play with these compressors. One has the sump under pressure from the high side, thus greatly increasing any oil dilution and requiring a heater to assist in keeping the oil refrigerant free. Then there are the low-side housing designs, where the suction side of the compressor is drawing through the compressor housing, thus greatly minimizing any dissolved refrigerant. The early DR machines are high-side dome; while the newer CK are low-side dome. I've been using Natioinal Refrigerants brand 150 vis. alkylbenzene oil and R152A in my Frigidaire projects. There is apparently a significant solubility of R152A in the oil, based on "observed" effects. Several times, while learning the ins and outs of these; I had to shut down a unit and take the evaporator apart for float adjustments. There is often a quite a bit of trapped oil in the evaporator header. It continues to "fizz" and offgas refrigerant for quite a while, even to the extent that I have taken the evaporator apart, made repairs, and put it back together.... and then when connecting the vacuum pump there is a lot of loud popping and boiling where the oil releases dissolved refrigerant! That surprised me the first time. Also, the Frigidaire belt-drive reciprocating compressors are oil-sealed and meter a constant moderate amount of oil out with the hot gas. This oil goes through the condenser and receiver. The mixture passing the sight glass is as clear as water; indicating to me that the amount of oil passing the compressor is low enough that it is able to fully mix with the liquid refrigerant. I was expecting to see some sort of beading of oil, or a cloudy emulsion but that's just not what it does. Some day I want to get a glass cylinder test apparatus where we can mix oils and refrigerants and really observe what happens. That would be very interesting! EDIT: One more thing I want to mention about non-Monitor Top systems; specifically other vintage low HP refrigerating systems. The vast majority of them are low-side dome designs. The standard design for decades has been the low-side dome compressor, with a capillary tube metering system and heat exchanger on the return line. The warm liquid from the condenser passes through a copper capillary tube soldered to the side of the cool vapor return from the evaporator. The compressor never sees any liquid returning. The charge volume and the amount of superheat in the returning gas (as a result of the heat exchanger) ensures that only dry vapor returns. Any oil pumped out by the compressor flows along the walls of the tubing, in a film, and drips back into the compressor with the return gas. The sump temperature is very hot on these designs. There should be no liquid and very little refrigerant dissolving in the oil, because of the very hot temperature and low pressure. The only time oil miscibility is a factor for the compressor is in the event of a flooded start. In general, the ratio of liquid refrigerant to oil is low enough that the flooded start will pass without damage. Sometimes you can hear this, if the system has been stopped a long time. There will be a popping or crackling sound from the sump as the sudden lowering of pressure causes the refrigerant to boil out of the oil! The CK Monitor Top is famous for this. |
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