Support
In practice , it is difficult to find out how much oil is circulating with the refrigerant . On larger equipment , you can observe the oil level in the crankcase . However , if oil has been added , the crankcase level may not indicate the correct oil charge .
A loss of capacity might indicate excess oil in the evaporator . When there is oil in the evaporator , several factors determine whether or not it remains or is circulated by the refrigerant returning the oil to the compressor :
• The geometry of the piping ( line sizing , bends , elbows , restrictions , vertical risers , slope ).
• The velocity of the refrigerant gas .
• The viscosity or fluidity of the oil . Oil itself is quite fluid and has a relatively low viscosity at ordinary temperatures . At lower temperatures , the oil becomes more viscous ( more difficult to pour ). Whether refrigerant vapour can push oil out of the evaporator depends on how fluid or viscous the oil is . Remember that refrigerant itself has very low viscosity . Solutions of oil and refrigerant have a viscosity between that of the oil and that of the refrigerant . As more oil dissolves in the refrigerant , the solution becomes more viscous .
As a matter of interest , you might assume that oil is most difficult to move in the coldest part of the evaporator , but viscosity measurements show that this is not so . Refrigerant is more soluble in oil at low temperatures than at high temperatures at the same pressure .
So , Gordon , in summing up , remember that the compressor may not be properly lubricated if too much oil circulates with the refrigerant . In solving the issue : install oil separators , make sure your refrigerant line sizing is correct and correctly installed , make sure that the necessary P-traps are installed correctly , check that the system components have been correctly selected and finally check that you have used the correct oil for the system in question .
REFERENCE :
1 . ACRA
Thank you for all your questions . Send your problems ( and sometimes your creative solutions ) to acra @ netactive . co . za with ‘ Solutions Page ’ in the subject line . You may include pictures . RACA
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RACA Journal I October 2021 www . hvacronline . co . za