RE: Required pipeline water velocity to flush air from line

Hi Steve,

The buoyant force (Archimede's Principle) says: Fb=Rho.V.g where: (vertical pipe)

Rho = density of the fluid

V = Volume of submerged object

g= gravitational acceleration.

If the inclination of the pipe is alpha, then FB = Rho.V.g.tg alpha

The drag force is: Fd = Cf.S.v , where:

Cf= coefficient : = 0.45 for a sphere

S= section of the object

V: velocity of the fluid.

To sweep the air along with the fluid Fd should be greater then Fb

I hope this helps,

Erik

Van: PipingDesign@yahoogroups.com [mailto:PipingDesign@yahoogroups.com] Namens Steve McKenzie
Verzonden: Friday, February 22, 2008 9:54 PM Aan: PipingDesign@yahoogroups.com
Onderwerp: [PipingDesign] Required pipeline water velocity to flush air from line

Gents
With a water pipeline containing air, it is common practice to install air eliminators at the high points. However it should be possible to use the water to sweep the air along with it if the water velocity is sufficiently high. I could have a shot at calculating the velocity, but the assumptions would have to be on the simplistic side. The essential problem is to find the water velocity in a pipe of given downwards inclination, where the buoyancy force of the air bubbles equals the downwards drag force of the water on the air. The major independent variables would appear to be; pipe diameter, roughness, inclination, effective water depth in the pipe, air viscosity and density/pressure. Any help of referrals would be appreciated.

Cheers

Steve Mckenzie

<http://1232432.sigclick.mailinfo.com/sigclick/05030104/0505034D/054D0014126 161.jpg>

[Non-text portions of this message have been removed] Received on Sun Feb 24 05:48:00 2008