Friction factor unsteady-state flow
Friction factor unsteady-state flow
(OP)
Hello everybody,
I trying to collect some informations for what is concering the friction factor behavior in unsteady-state flow of water in fittings, such as elbows, reducers and so on, because the friction factor is defined for steady-state flow and i'm developing a model for an hydraulic closed loop and i would like to study it also in unsteady-state . Is anyone of you so kind that could give me some information or at least tell me where a can find anything on this matter?
Thank you in advance i'd really appreciate
Luca
I trying to collect some informations for what is concering the friction factor behavior in unsteady-state flow of water in fittings, such as elbows, reducers and so on, because the friction factor is defined for steady-state flow and i'm developing a model for an hydraulic closed loop and i would like to study it also in unsteady-state . Is anyone of you so kind that could give me some information or at least tell me where a can find anything on this matter?
Thank you in advance i'd really appreciate
Luca





RE: Friction factor unsteady-state flow
"If stupidity got us into this mess, then why can't it get us out?" - Will Rogers (1879-1935) ***************
http://virtualpipeline.spaces.live.com/
RE: Friction factor unsteady-state flow
Have a look in the FAQ section of this forum for the article by quark which discusses the analytical expressions for friction factor. This will make it easy to generate an algebraic expression to include in your analysis.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Friction factor unsteady-state flow
pg 47
"From this brief review, it becomes apparent that friction effects in nonsteay flow depend not only on the instantaneous flow conditions but also on the history of the flow."
Regards
RE: Friction factor unsteady-state flow
"If stupidity got us into this mess, then why can't it get us out?" - Will Rogers (1879-1935) ***************
http://virtualpipeline.spaces.live.com/
RE: Friction factor unsteady-state flow
RE: Friction factor unsteady-state flow
"If stupidity got us into this mess, then why can't it get us out?" - Will Rogers (1879-1935) ***************
http://virtualpipeline.spaces.live.com/
RE: Friction factor unsteady-state flow
Yup! :)
RE: Friction factor unsteady-state flow
But:
In steady incompressible flow, the local friction factor is constant when the velocity profile is fully developed (and not changing).
For a short pipe, say L/D< about 60, with turbulence, the velociy profile is not fully developed. Hence, use of a Moody chart will not give a reliable friction factor.
For very long pipes, the effect of the length to obtain fully developed flow is generally neglected.
Further, if the flow is compressible, the velocity profile is changing, along with the local friction factor.
Regards