Hi, I am a little beat confused with Re Number. I have an inlet pipe with a D diameter. This pipe is connected with a valve, in which moves a piston. Now my question. Should I evaluate my Re number with inlet pipe (eg. with D diameter), or should I take into account the piston opening? In the last case, Re number is fully dependant of piston opening, and describe much more the flow characteristics. Any Advice? Thanks a lot.

Hi mAx

i feel that the concept of wetted area would be very much appicable for this case

for estimating the Re of an annulus we need to used piston in the pipe

i think mean hydraulic diameter should be used for estimation of Re in the above case

bye Ravi Kiran

Hi Ravi, Thanks four your reply. This is what I was thiking too.