Refrigerant / oil seperation in low velocity flow - suction accumulator

Hello,

The little self contained water chiller I am building needs a suction accumulator.

Ideally the suction line will be 3/8" OD, however the most appropriate suction accumulator I have found (going from the manufacturers tables for refrigeration capacity, pressure drop, oil return rate) has 5/8" connections (and presumably 5/8" internal U-tube).

This would give a much lower vapour velocity than the suction line.
My question is:

- Is seperation of the oil from the refrigerant a problem in very short lengths of vertical line (i.e. a few inches) or is it only a problem in longer pipes?


Cheers All,

James.

I may have answered my own question. This Refrigeration Research datasheet:

http://www.refresearch.com/Portals/26/PDF/54.pdf

states:
"SELECTION OF SUCTION ACCUMULATOR – The suction accumulator should not necessarily be selected to have the same size inlet and outlet as the compressor suction line. It is more important to select the suction accumulator well within the limits of (1) pressure drop, (2) oil return as shown on the following page and (3) total amount of charge to be held"

But I'd still like to know how long a section of pipe needs to be before you need to apply strict sizing for flow velocity / oil return. What is the general feeling on this?

Thanks for any help,

James.