Pipe Flow: Neglecting Pipe Length

In summary, the conversation discusses a pipe with standard concrete that carries standard water from point A to point B. The issue at hand is finding the correct velocity at point B, given the long distance between the two points. The use of Bernoulli's equation is mentioned, but there is concern about neglecting the length of the pipe and the potential reduction of velocity due to heat and energy dissipation. It is noted that this topic is not commonly covered in introductory courses.
  • #1
joejoekelly1
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In the diagram attached I have a pipe (standard concrete) that is going from point A (Entrance) to point B (Exit). Standard water is the fluid within the pipe. Point A (entrance) has a constant uninterrupted supply of water at a velocity of 0.7m/s, how do I find the correct velocity at point B (Exit), given that the distance is between point A and Point B is very long? This problem is going around in my head for quite some time now. I have used Bernoulli’s equation to solve for V at point B but I am concerned about the length of the pipe and that neglecting it may be over simplifying the problem. Could it not reduce the velocity over a long distance?
 

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  • #2
Yes it could. Any fluid with finite viscosity moving past any kind of rough surface would generate heat and thus dissipate some of the kinetic energy of the fluid.

This subject is not typically covered in an introductory course.
 

1. What is pipe flow?

Pipe flow refers to the movement of fluid, typically a liquid or gas, through a pipe or conduit. It is an important concept in fluid mechanics and is used in various applications such as plumbing, chemical engineering, and hydraulics.

2. What does it mean to neglect pipe length in pipe flow?

Neglecting pipe length in pipe flow means assuming that the length of the pipe has no significant impact on the flow rate or pressure drop. This simplifies the calculations and analysis of the flow, but it is only applicable in certain situations where the pipe length is much greater than the diameter and the fluid properties remain unchanged throughout the length of the pipe.

3. Why is pipe length neglected in some cases?

Pipe length is often neglected in cases where it is significantly longer than the diameter of the pipe, as it has a minimal effect on the flow rate. It is also assumed to be negligible when analyzing laminar flow, where the fluid particles move in parallel layers with no disruption from the pipe walls.

4. What are the limitations of neglecting pipe length in pipe flow?

Neglecting pipe length can lead to inaccurate results in certain situations. For example, in turbulent flow, neglecting pipe length can underestimate the pressure drop and overestimate the flow rate. It is also not applicable when analyzing pressure variations along the length of the pipe, such as in a pump system.

5. How is pipe length accounted for in pipe flow calculations?

In cases where pipe length cannot be neglected, it is included in the calculations using the Darcy-Weisbach equation or other methods such as the Hazen-Williams equation. These equations take into account the length of the pipe, along with other factors such as diameter, roughness, and flow rate, to determine the pressure drop and flow rate.

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