Hi

I'm about to size a vertical riser on a CO2 suction line. But I’m finding it very difficult to obtain some proper design guideline.

If I look in my ASHRAE Handbook (2010 edition - the one with a CO2 chapter), they simply refer to riser sizing in the halocarbon section. The halocarbon section has a lot of tables for different refrigerants but none for CO2 (as far as I can see).

So what method do you guys use to ensure proper annular flow in your CO2 risers?

One method I’ve been thinking about trying, to use Bernoulli’s equation for pressure (and thereby force acting on a particle). But this doesn’t really apply to the annular flow profile.

I've also been thinking about scaling one of the known tables from ASHRAE with the difference in density. But once again, density most relates to buoyancy and less to the friction forces driving the oil up the tube walls.

Any ideas are much appreciated. I know that most of our design guidelines are made from good old experience and trial-and-error, but if you got any sources/documents to include i would be perfect.