Volume Flow Rate in a Pipe for Viscous Fluid

  • Thread starter jde23
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  • #1
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Homework Statement



Hi, my first post here! I have a Thermodynamics resit over the summer and I'm trying to get my head around viscous flow, I'm stuck at a question and need help! Thanks :)

Glycerine discharges to the atmosphere through a circular pipe 100mm in diameter. The gauge pressure 50m from the exit is 458 kPa. Data for glycerine: ρ=1260 kg/m^3, μ=0.9 kg/ms.

Determine the volume flow rate Q for the following cases:
(i) a horizontal pipe (verify the flow is laminar!) (Ans: 25 litres/s)
(ii) a pipe inclined upwards by 20° (Ans: 13.5 litres/s)
(iii) a pipe inclined downwards by 20° (Ans: 36.5 litres/s)

Homework Equations



I thought this equation was the right one to use but my answer is totally wrong when I plug the numbers in, it's not a units thing either...

Q = (∏d^4 / 128μ) * (ΔPloss / length)

The Attempt at a Solution



I assumed the gauge pressure at the pipe exit is equal to atm pressure, so 100kPa - is this correct? The rest is just plugging numbers in. Am I missing something obvious here...?
 

Answers and Replies

  • #2
rock.freak667
Homework Helper
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Have you tried using Bernoulli's equation?
 
  • #3
1,198
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Your formula works. I get 25 for part i. Are you mixing gauge pressure and absolute pressure?
 
  • #4
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Hi LawrenceC, yes I think I am! Embarrassing moment, whoops...

Thanks!
 

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