View Full Version : Gas velocity in vertical risers to ensure proper oil return

07-03-2012, 08:28 AM

I'm about to size a vertical riser on a CO2 suction line. But Iím 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 Iíve been thinking about trying, to use Bernoulliís equation for pressure (and thereby force acting on a particle). But this doesnít 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.

12-03-2012, 06:48 AM
Are you sizing a transcritical or cascade system?

12-03-2012, 06:55 AM
The IIAR have a cascade Ammonia/CO2 book which includes a section on pipe sizing. You could also take a look on the BOC website.

20-03-2012, 05:05 PM

The Danish Research Institute
The Industrial Refrigeration Consortium at the University of Wisconsin, Madison, Mr. Todd Jekyl

The magic names for the math and the experimentation include:

John c Chan
And a host of others...The Russian work was the earliest definitive. The Web Address gives a flock of algebra derived from separate work by certain of these parties.