×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Head loss in partially-full pipe?

Head loss in partially-full pipe?

Head loss in partially-full pipe?

(OP)
Ok here is a dumb gear head (mechanical engineer) question for you sewer rats .  

I am trying to estimate head loss in a partially full pipe.  Good old Round Pipe, NOT a trapezoidal or rectangular channel or wood flume or etc.  I have looked in all my references (Crane, Cameron, Marks, Lindeberg, Streeter & Wylie, etc.) but none _definitively_ say whether the Darcy equation, modified for hydraulic radius, is correctly applied to circular cross-sections, i.e. a pipe.  

I assume the procedure is to calculate the velocity using Manning, and then use that in the Darcy equation with the correct hydraulic radius for my flowrate and pipe size - yes?   

By the way, this is for design work for a new combined oily water/storm water/fire water sewer in a process plant.  I am dropping 60' in elevation from my source (tank diked area) to my collection point (below-grade sump tank, 1200' away) so I am working on line sizes, head loss, estimating the potential for hammer events, etc.  Thanks for your help!

Thanks!
Pete

RE: Head loss in partially-full pipe?

This really sounds more like a gravity sewer. No head loss. Use Manning's to get your Q.

Richard A. Cornelius, P.E.
WWW.amlinereast.com

RE: Head loss in partially-full pipe?

(OP)
Thanks Dick.  Yes this is a gravity sewer.

But... I don't understand why I don't need to consider friction loss.  It seems to me that the motive force supplied by sloping the pipe is offset by friction loss.  Why do I not need to consider that?  Isn't the theoretical Q predicted by Manning reduced by the amount of head lost due to friction, as would be the case for a full pipe?  Thanks!

Thanks!
Pete

RE: Head loss in partially-full pipe?

Isn't friction loss only a consideration when you have to size a pump & motor?  Why do you care?  Just point it down hill @ appropriate slope.

Also, why are worried about water hammer?

RE: Head loss in partially-full pipe?

Friction losses are taken into account by the 'n' value of the pipe.

Richard A. Cornelius, P.E.
WWW.amlinereast.com

RE: Head loss in partially-full pipe?

bio:
Friction decreases the capacity of the pipe.  Insufficient capacity could overtop the diked with oily water.

74:
Just run Manning's for full flow, as dick said.  It isn't going to change much for partial flow.  At 5% you should be fine, and velocity shouldn't get excessive.  But with 60' of head, plus however deep your diked volume is, you might get a reduced diameter using Hazen-Williams or Darcys.  If the oil content is high, use Darcy's to accurately account for density.  Finally, again due to the potentially huge difference between headwater and tailwater, run a culvert check, for type of control, with conservative inlet loss and minimum tailwater.  You don't want to design too close and flood that dike.

Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve

RE: Head loss in partially-full pipe?

Download flowpro2 freeware for gravity line simulation

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources