Fluid Mechanics Theoretical Pipe Diameter

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SUMMARY

The discussion focuses on calculating the pipe diameter and mean velocity in fluid mechanics using the equation Mean velocity = 4Q/πD², where Q is the volumetric flow rate. The user provided parameters include Q = 0.01 m³/s, density = 960 kg/m³, viscosity = 0.081 Pa·s, and max velocity = 1.8 m/s. It was established that for laminar flow, the mean velocity is half of the maximum velocity, and the Reynolds number calculated was 1280, confirming laminar flow conditions. Proper unit representation and equation formatting were emphasized as critical for accurate calculations.

PREREQUISITES
  • Understanding of fluid mechanics principles
  • Familiarity with the Reynolds number and its significance
  • Proficiency in using the equation for mean velocity in pipe flow
  • Knowledge of laminar and turbulent flow characteristics
NEXT STEPS
  • Learn how to calculate the Reynolds number for different flow conditions
  • Study the effects of viscosity and density on fluid flow in pipes
  • Explore the transition criteria between laminar and turbulent flow
  • Investigate the impact of pipe diameter on flow rates and velocities
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Students and professionals in engineering, particularly those specializing in fluid mechanics, hydraulic engineers, and anyone involved in designing or analyzing pipe systems.

eastend111
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Homework Statement


I need to find the pipe diameter or mean velocity.
Q= 0.01m^3s
Density= 960kg m^3
Viscosity = 0.081 Pa s
Max Velocity = 1.8 m s

Homework Equations


Mean velocity= 4Q/pi.D^2

The Attempt at a Solution


I have two unknowns in this equation so I'm unable to find D or Mean Velocity. Am I right in thinking the mean velocity is max velocity/2? And does this work for laminar/Turbulent/transitional flow? Any help appreciated. Thanks
 
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eastend111 said:
Q= 0.01m^3s
Density= 960kg m^3
Viscosity = 0.081 Pa s
Max Velocity = 1.8 m s
Even I know that velocity does not have units of m s :eek:

Your first priority should be to show units correctly. Not only will it help discipline your thinking, but units correctly incorporated into equations allow an independent check of formulae.

Please fix all the units, and show them correctly in a follow-up post.
eastend111 said:

Homework Equations


Mean velocity= 4Q/pi.D^2
Another example of sloppiness. :mad: This desperately needs some parentheses to make it correct.
 
eastend111 said:

Homework Statement


I need to find the pipe diameter or mean velocity.
Q= 0.01m^3s
Density= 960kg m^3
Viscosity = 0.081 Pa s
Max Velocity = 1.8 m s

Homework Equations


Mean velocity= 4Q/pi.D^2

The Attempt at a Solution


I have two unknowns in this equation so I'm unable to find D or Mean Velocity. Am I right in thinking the mean velocity is max velocity/2? And does this work for laminar/Turbulent/transitional flow? Any help appreciated. Thanks
They must be referring to laminar flow, where the maximum velocity is twice the average velocity. In turbulent flow, the ratio is much closer to 1. As a check on this, once you find the diameter for laminar flow, you should calculate the Reynolds number to make sure that the laminar-turbulent transition hasn't been exceeded. If it has, then you need to start looking at the case of turbulent flow.
 
Thanks for your reply, much appreciated. I have divided by 2 to get the mean velocity. I've then plugged it into the Reynolds Number formula to get 1280. Which means it is laminar flow.
 

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