minimum fluid velocity in small refrigeration systems

[subjectin]

Considering a basic, relatively small (1/5 ton) condenser/txv/evaporator/compressor refrigeration system, does any standard for the minimum refrigerant fluid velocity for compressor oil return exist? The tubing would be copper with diameters less than 3/8" OD. I can locate the rule of thumb of 1200 feet per min for large industrial systems with large piping rises, but I have been unsuccessful in locating any such info for small systems.

I have posted this in the fluid forum as well. Thanks for any info.