Calculation of absorbed R-134a in compressor oil

[desA]

I have been developing a refrigerant charge calculation procedure for a heat-pump circuit.

The part that currently needs some work is that for an estimate of the mass of R-134a refrigerant absorbed by the compressor POE oil.

If anyone has links to a suitable reference article, or link, I would be most grateful.

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Practical test:
During a vacuum pump-down of my lab heat-pump, prior to re-gassing, I listened to the compressor (scroll) as the vacuum pump began pulling. The sound of gas bubbling was very evident. As the vacuum level increased, the base of the compressor became cold (sweat) & reduced in temperature off atmospheric, by around 15'C. The sweat line was some 70% of the distance from base to suction inlet. The de-gassing phase took quite some time to complete.

[Chef]

I have a couple of pdf with some good info but cant find the link. Send me a PM with your email and I will send it to you.

Chef

[Gary]

Practical test:
During a vacuum pump-down of my lab heat-pump, prior to re-gassing, I listened to the compressor (scroll) as the vacuum pump began pulling. The sound of gas bubbling was very evident. As the vacuum level increased, the base of the compressor became cold (sweat) & reduced in temperature off atmospheric, by around 15'C. The sweat line was some 70% of the distance from base to suction inlet. The de-gassing phase took quite some time to complete.

I'm guessing the entire charge found its way to the compressor while the system was off.

[desA]

I have a couple of pdf with some good info but cant find the link. Send me a PM with your email and I will send it to you.

Chef

Thanks, Chef.

PM sent, including e-mail address.

[Chef]

The pdf's are sent. you may also like to look at this

http://findarticles.com/p/articles/m...g=content;col1

It has all the calculations you need but is a bit hard to follow.

Chef

[desA]

The pdf's are sent. you may also like to look at this

http://findarticles.com/p/articles/m...g=content;col1

It has all the calculations you need but is a bit hard to follow.

Chef

Thanks so much for the articles. I'll continue per e-mail on the specifics.

[desA]

I'm guessing the entire charge found its way to the compressor while the system was off.

I tend to agree with you. The unit had stood for some time & was de-gassed directly off this storage position.

The off-gassing sounded like fluid flowing inside the compressor shell, at first. The give-away was the temperature drop in the shell as the refrigerant gassed off.

All very interesting & got me thinking about how much gas is actually generally entrained in the compressor oil during operating conditions. The main reservoir is estimated to be in the compressor shell (scroll-type), due to its 'accumulator-type' design.

[Gary]

When a system is off, the refrigerant will migrate to the coolest point, which is usually the evaporator.

If the suction line is a straight run downwards to the compressor, the refrigerant will be delivered by gravity to the compressor.

For this reason it is good practice to have the suction line go up to the top of the evaporator and then down to the compressor. This traps the liquid in the evaporator.

But if the compressor should become the coolest part of the system the trap won't stop the refrigerant from migrating to the compressor.

If this is a possibility then a crankcase heater is added to prevent the compressor from becoming the coolest part of the system.