I'm hoping that someone can put me on the right track here.

In the ASHRAE Handbook of Refrigeration 2006 SI Page 2.18 Table 19, they tabulate the minimum refrigeration capacity for oil entrainment up suction risers.

This might be useful if you are only using R22 or R134a but what would be more useful would be to know the basis of the table.

I would expect oil entrainment to be a function of gas velocity. So, given the cycle temperatures, I can back-calculate the equivalent suction gas velocity for each duty listed.

Now, I have a problem. The velocity is not constant!
But, there must be some reference condition that is used as a basis for generating this table.

Here is a sample of my calculated velocities.

Minimum velocity [m/s] for oil entrainment in suction risers
R22
te sh 12 15 18 22 28 35 42 54 67 79 105 130
-40 5 3.3 3.5 3.9 5.1 5.4 6.1 7.0 7.6 7.1 9.1 10.6 11.9
-40 15 3.2 3.4 3.7 4.8 5.1 5.8 6.6 7.3 8.1 8.6 10.1 11.3
-40 25 3.1 3.3 3.6 4.7 5.0 5.6 6.4 7.1 7.9 8.4 9.8 11.0

-20 5 2.2 2.4 2.6 3.4 3.6 4.1 4.7 5.1 5.7 6.1 7.1 7.9
-20 15 2.1 2.2 2.5 3.2 3.4 3.9 4.4 4.9 5.4 5.8 6.8 7.6
-20 25 2.0 2.2 2.4 3.1 3.3 3.8 4.3 4.7 5.3 5.6 6.6 7.3

-5 5 1.7 1.8 2.0 2.6 2.8 3.2 3.6 4.0 4.4 4.7 5.5 6.2
-5 15 1.6 1.7 1.9 2.5 2.7 3.0 3.4 3.8 4.2 4.5 5.3 5.9
-5 25 1.6 1.7 1.8 2.4 2.6 2.9 3.3 3.6 4.1 4.3 5.1 5.7

5 5 1.5 1.6 1.7 2.3 2.4 2.7 3.1 3.4 3.8 4.1 4.8 5.3
5 15 1.4 1.5 1.6 2.1 2.3 2.6 2.9 3.2 3.6 3.8 4.5 5.0
5 25 1.3 1.4 1.6 2.0 2.2 2.5 2.8 3.1 3.5 3.7 4.3 4.8

Do you have any ideas about this?