Oil draining port position?(HFC,HCFC)

[sagittarius]

Dear all,
This is an old question. BUt it is puzzling me now. I want to know the position of oil draining in the flooded evaporator.
R717 with mineral oil, the oil draining port set on the bottom; R22 with mineral oil , the ports set on the upper liquid level.'Cause the mineral oil and R22/R717 is immiscible.
But to R507 with miscible oil, R23 with miscible oil, where is the position to set in the flooded evaporater?I met this matter in the R507/R23 cascade system. High temperature stage condensing temp. is 40C, evaporate temp.is -25C. Low stage running condition is -20C(condensing)/-75C (evaporating).

kindly regards,

sagittarius

[CanadianIce]

From what I've seen, if the refrigerant and oil are miscible, then you would set your oil drains at operating level. We set lines at 3 different levels, all slightly overlapping vertically to allow for surging of liquid. These are piped back to the oil still.

[sagittarius]

I'm confused about that. It's the reason I bring up the question.
Miscible oil will blend with refrigeration at any liquid level. Whether you set the oil drain ports at the operation level or the bottom of vessle,the oil can't be drained mainly. THis is my puzzle.