×
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

Capilar design

Capilar design

Capilar design

(OP)
Hello everybody,

I am driving nuts with a very easy problem ...In fact i would like to control my flow rate using the concept of capilarity. My flow rate is 15.8 lpm, my tubing is 3/16in so i ve calculated my maximum speed inside the tubing. Then i've found the desired capilar diameter for a desired flow rate of 1.78 lpm...I've found 0.063 in...(Q=V*A)
Unfortunatly this design its not controlling nothing...Where is my mistake?? What sould i do instead of that?
I really apreciate your answer here
Greg

RE: Capilar design

If the unit "lpm" means a liter per minute then you are in a range of an usual rotameter or a turbine flow meter (~400$). If you still insist to use a capillary tube then you should measure a delta P across the tube and this will be in correlation to your flow.
Your mistake is that you do not measure anything that correlates and changes with flow.
m777182

RE: Capilar design

You did not define what is limiting the maximum speed.

There might be 3 cases to limiting the max speed in a capillary tube:

acoustically choked - for a compressible fluid ,the speed of sound would limit the velocity. In the case of a very short capillary ( L/d <3) then line friction could be ignored, but line geometry may cause oblique shick waves to form and this would limit the flow.

frictionally choked, compressible flow- for an L/d > 3 ( and usually in the range of 3- 100) one would have frictionally choked curves, usually approximated as adiatic flow, using the Fanno curves and its definining equations for a perfect gas

frictionally choked, incompressible or 2-phase flow- coventional pressure drop equations can predict the choke flowrate.

RE: Capilar design

(OP)
Thank you for your answers.

What is limiting my maximum speed here is in fact my pump (15.8 liter per minute, vacuum at 15 in of mercury, size of 3/16 in I.D). I am pumping ambient air. Regarding my problem, could you give me more precision about :

frictionally choked, compressible flow- for an L/d > 3 ( and usually in the range of 3- 100) one would have frictionally choked curves, usually approximated as adiatic flow, using the Fanno curves and its definining equations for a perfect gas.

Best regards and thanks again,

Greg

RE: Capilar design

For typical frictionally choked flow in a pipeline with compressible fluid, see thread 378-6648.

For a short pipe which behaves as an orifice, see thread 798-51260, or se A.J. Ward-Smith Int J Heat Fluid V1 no 3 pp123-132 1979

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