Annular flow

JWilliams

I have flow in an annulus. The flow enters perpendicular to the annulus and exits perpendicular also. The behavior I am seeing is when I vary the nozzle size, 2",4",6", I am obtaining counter-intuitive results. With the larger diameter nozzles at the entrance and exit, I am receiving larger pressure drops. It would make sense that the smaller the diameter, the higher the pressure drop. I've tested both constant velocities and constant volumetric flow rates through the various size nozzles. I have also obtained k-values (minor loss coefficients), and can accurately predict the pressure drop varying flowrates, but again still counter-intuitive with respect to nozzle diameters.

Is there some anomaly with annular flow that causes this or is something inherently wrong with my models?

If anyone has any insight, it would greatly be appreciated.

Thanks.