×
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

Flow rate inside concentric tubes

Flow rate inside concentric tubes

Flow rate inside concentric tubes

(OP)
I have a problem dealing with concentric tubes. Technically, the internal one is a solid rod, and the flow is flowing between the inside of the large diameter tube and the outside of the rod (of course). Current flow rate is 9 gal/min. The inside rod is 10 mm, and outside tube is 15 mm (internal dia). We are going to a 6 mm inside rod, and want to keep flow rate at 9 gal/min. Now, I know the flow rate equation is

Q=A*Velocity

So I solved for velocity, with Q/A.

Q = 9 gal/min = 567,823.3 mm^3/s
A = pi/2*(15^2-10^2) = 196.35 mm^2

So, V = 2891.9 mm/s

Now, I don't think I want to change the velocity (unless anyone knows of a reason that I don't), so basically I just need the area's to remain the same...

pi/2*(15^2-10^2) = pi/2(x^2 - 6^2)
x = 9.43 mm

Correct? Seems simple enough, but just looking for a confirmation that I dont need to change the velocity for any reason....Just wanted to check, though.

RE: Flow rate inside concentric tubes

I'm not huge into piping but my work has recently had me going through piping systems.  So I can't speak with 100% authority on the subject, but I can give you my opinion on what I would do.  

The only concern you should have with the velocity is pressure drop.  Obviously higher velocities lead to higher pressure losses.  Now the flow, flow area and the velocity may be the same but from what I remember your hydraulic diameter will be different (your new concentric tube has a smaller hydraulic diameter).  So you will want to look at the frictional losses to make sure that they haven't increased.

RE: Flow rate inside concentric tubes

Not exactly.  See Chapter 5 of this doc,

http://txspace.tamu.edu/bitstream/handle/1969.1/4334/etd-tamu-2006B-PETE-viloria.pdf?sequence=1

**********************
"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic  (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Flow rate inside concentric tubes

In the calculation of circular area you need to use pi/4 when using diameters^2.  r = d/2   r^2 = (d^2)/4

A = pi*(D^2-d^2)/4 = pi*(R^2-r^2)

Ted

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