Speed of water flowing through pipe

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SUMMARY

The discussion focuses on calculating the volume flow rate of water in a piping system with a 4-inch diameter section, where the speed of water is given as 3.0 ft/s. The volume flow rate can be determined using the formula Q = A x V, where A is the cross-sectional area of the pipe and V is the velocity of the water. The area is calculated using the formula A = πr², and the flow rate remains constant throughout the system due to the principle of conservation of mass. The discussion also addresses the relationship between pipe diameter and water velocity, confirming that as the diameter decreases, the velocity increases while maintaining the same flow rate.

PREREQUISITES
  • Understanding of fluid dynamics principles
  • Familiarity with the formula for cross-sectional area (A = πr²)
  • Knowledge of the conservation of mass in fluid flow
  • Basic algebra for solving equations
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  • Calculate flow rate using the formula Q = A x V for different pipe diameters
  • Explore the implications of incompressible flow in fluid dynamics
  • Learn about the continuity equation in fluid mechanics
  • Investigate how changes in pipe diameter affect flow velocity
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Students studying fluid mechanics, engineers working with piping systems, and anyone involved in hydraulic design or analysis.

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Homework Statement


The speed of water flowing through the "influent" 4-inch diameter section of the piping system below is 3.0 ft/s. What is the volume flow rate of water in the piping system? Express the volume flow rate in ft^3/s


Homework Equations





The Attempt at a Solution


I really don't know what to do. I know pi*r^2 comes into play here, but I need help. Just tell me how to start and guide me through it please.
2012-11-07%252021.12.49.jpg
 
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Flow rate = area of the pipe multiplied by the velocity.

You have everything but the flow rate. The area of the pipe is pi*r^2 as you said. Since you're not given a second density we can assume the flow is incompressible, and due to the conservation of mass, the flow rate in the 3 in dimater pipe will be the same. Q1 = Q2. I can't give you anymore without solving it for you.
 
Given that the fluid is water, it's safe to assume that the fluid is incompressible.
 
Vadar2012 said:
... the flow rate in the 3 in dimater pipe will be the same. Q1 = Q2.
Can the speed of the water be different even though the flow rate is the same? Part two says to find the speed of the water in the 3-inch diameter section in ft/s
 
Yes.
 
thatshowifeel said:
Can the speed of the water be different even though the flow rate is the same? Part two says to find the speed of the water in the 3-inch diameter section in ft/s

Yes, this is connected to the equation given by vadar2012: flow rate = area x velocity.
The flow rates are the same everywhere in the pipe (it must be, the water doesn't disappear). Therefore, if the area of the pipe increases, the velocity decreases.

So:
step 1: calculate flow rate = area x velocity or Q1=A1 x V1
step 2: use Q1 = Q2 to calculate V2
 

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