Blended Refrigerants & Oil carryover

[Mark II]

Guys,

In my short membership of this site i have noticed a significant amount of issues relating to Oil carryover..
I just wanted to share my experiance with this issue in retrofitted & dedicated blended systems..
At the time of phase out, i was doing a significant amount of trawler work All Bitzers (Bitzer crap purchased @ auctions & made to work somehow). There were 8 new gasses & 3 new oils coming out everyday.. Because of this chaos, we didn't retrofit anything until we had no option..
We did however work on a significant number of migratory boats that had been retrofitted & weren't performing.
High Discharge temps & pressures / High Oil carryover / Burned Oil.
In the space of 1 month i looked at 3 systems with broken discharge valves .. All 3 had water cooled heads (small Head volume)
This indicated that the expansion of blended refrigerants in the compression phase was far more severe than it was with *****s.
From that point i upgraded every discharge valve, discharge line, oil seprator ( Equal size to Suction) right through to the condensor, ( approx 50 boats..)

This by itself ..
Eliminated Oil Carryover. Reduced Discharge pressure to the point that condensor flows required regulating to maintain pressure drop. Oil would come out looking clean. Refig performance 100% improvement, in most cases better than they ran on *****
I'm not convinced that manufacturers are designing Blend friendly systems to this day..

Hope this helps someone..

[monkey spanners]

Interesting post Mark.

Cheers Jon

[jcook1982]

So upgrading the line size helped slow down the velocity of the refrigerant which in turn allowed the system to not carry the oil to the parts of the system that shouldn't have oil?

[NoNickName]

I don't get the whole posting. What do you mean by: "the expansion of blended refrigerants in the compression phase was far more severe than it was with *****s"?

And what did you exactly upgrade? You mean you oversized?

[Mark II]

I don't get the whole posting. What do you mean by: "the expansion of blended refrigerants in the compression phase was far more severe than it was with *****s"?

And what did you exactly upgrade? You mean you oversized?

Nick,

I mean if it had a 3/4" discharge service valve, I;d fit a 7/8" & bring that up to a 1"1/8 oil sep, Most of the marine stuff here had Northside Condensers that had an 1"1/8 connection that had been reduced back down.. I'd run the whole line in 1"1/8..

With ***** if you ran a nice low superheat you could run a nice steady oil temp..You could see oil in the oil return line not foam.. I have found with blends,,As soon as you get the superheat down to where it should be the compressors/ oil & discharge all heat up.. How many MOP valves were we fitting to ***** systems ??

[NoNickName]

I can't follow you.
First, pipe size should not be a guess or a trial and error game. There are gazillions of pages about how to size the three refrigeration lines properly. I'm not ready to take the advice about increasing pipe sizes just based on experience.

Secondly I can't follow you on the oil to foam thing. Are you saying that blends are more prone to foaming? What refrigerants, what oil?

Thirdly, why on earth a low superheat in a blended refrigerant causes high discharge temperature, while the opposite is the case with single-component refrigerants?

[Mark II]

I can't follow you.
First, pipe size should not be a guess or a trial and error game. There are gazillions of pages about how to size the three refrigeration lines properly. I'm not ready to take the advice about increasing pipe sizes just based on experience.

Secondly I can't follow you on the oil to foam thing. Are you saying that blends are more prone to foaming? What refrigerants, what oil?

Thirdly, why on earth a low superheat in a blended refrigerant causes high discharge temperature, while the opposite is the case with single-component refrigerants?

Nick,

FIRST: You don't have to take my advice.
The discharge line is the shortest run in the system. On a condensing unit ,1?2? meters ? Trawler 3? 4 meters ?.. You're old enough to remember that retrofitting was a trial & error game..Key Note Speakers @ trade nights would tell us that: "A sight glass, is no longer a sight Glass You will never clear them.. T/X valves do run on flash gas after all"..
Synthetic Oil was being sold in Plastic containers & spoiling on the shelf..& Every new Refrigerant on the market was better than every other refigerant on the market..

Second: 507 EAL32.. 404 EAL32.. This may disturb you greatly Nick,, but i inherited a fleet off a Fridgie who moved up to Cooktown to replace the one who blew himself up pressure testing with Oxy..(30 years exp).
All his boats were on 507 & 3GS.. Oil came out Clear everytime.. These things get a Hot Start every trip.. Tonnes of salt water pumped into the deckboxes as they steam out. They endure prolonged periods of high load.. If there is a high flow of foaming oil pissing though the return line the sump will get hotter & hotter..

Third: If a retrofitted system is stuggling with Oil Carryover.. Lowering the superheat will not decrease the sump temp at all..

[desA]

Very interesting thread, indeed, Mark II.

If you could perhaps take dimensions of a few examples you've mentioned - including compressor details, operating pressures, temps - we could have a look at what exactly is going on in the system both before (on R22) & after (blends). We can then check the line sizes properly, & all learn from your valuable experiences.

An ounce of hands-on learning is worth 1000 tonnes of guestimating. Your practical experiences are extremely valuable.

[Mark II]

Des,

I stopped doing Trawlers about 8 years ago.. These days i'm based at an industrial chemicals complex / Explosives plant doing mainly Ammonia work..

The basis of this thread is:There is higher veocity in the discharge phase of blended systems. Creating volume helps to slow it all down.. Allows oil to settle in the seperator & be retuned as oil without heating up the sump..

[harrykica84]

ya the oil will mes **** up

[NoNickName]

Nick,
"A sight glass, is no longer a sight Glass You will never clear them.. T/X valves do run on flash gas after all"..
Synthetic Oil was being sold in Plastic containers & spoiling on the shelf..& Every new Refrigerant on the market was better than every other refigerant on the market..

Now I follow you.

If there is a high flow of foaming oil pissing though the return line the sump will get hotter & hotter..

507 and 3GS do not like each other. MO and HFC should not be together in a circuit.

Third: If a retrofitted system is stuggling with Oil Carryover.. Lowering the superheat will not decrease the sump temp at all..

No, in fact increasing the superheat should decrease carry over and sump temperature.