Fluid force at the end of a pipe

In summary: From freshman physics, when you do a force balance on object A, you don't include the force object A exerts on object B. You only include the force object B exerts on object A. Didn't they teach you that when they covered Newton's law of action-reaction?In summary, pressure is exerted on the control volume by atmosphere (or the surrounding fluid) and you are trying to find out what is the magnitude and direction of this pressure.
  • #1
Sat D
11
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Consider the very standard pipe problem used to calculate the force required to hold a pipe with a bend that has some fluid flowing through it, as shown in the image. We use Newton's second law of motion to calculate the external force required. However, why is there pressure acting into the control volume at the right end of the pipe? How do you explain this?
Shouldn't the fluid flowing out generate a pressure (force) acting outward?
 

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Remember pressure in a fluid acts in all directions.
Unless the pressure at the outlet is zero, then the pressure there acts outward on the fluid moving into the next section of pipe, tank, or whatever, AND it acts inwards against the fluid behind it. And it also acts sideways on the walls of the pipe in all directions, though it may not be the same on all sides of the pipe if there is a pressure gradient perpendicular to the flow here.
 
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  • #3
Merlin3189 said:
Remember pressure in a fluid acts in all directions.
Unless the pressure at the outlet is zero, then the pressure there acts outward on the fluid moving into the next section of pipe, tank, or whatever, AND it acts inwards against the fluid behind it. And it also acts sideways on the walls of the pipe in all directions, though it may not be the same on all sides of the pipe if there is a pressure gradient perpendicular to the flow here.
So why don't we consider the pressure that is pointing outwards while writing out the force balance equations for the pipe?
 
  • #4
Sat D said:
So why don't we consider the pressure that is pointing outwards while writing out the force balance equations for the pipe?
From freshman physics, when you do a force balance on object A, you don't include the force object A exerts on object B. You only include the force object B exerts on object A. Didn't they teach you that when they covered Newton's law of action-reaction?
 
  • #5
In this you considered a control volume and you are trying to calculate what are the forces that are acting on the fluid in the control volume. On the right side the pressure is exerted on the control volume by atmosphere (or the surrounding fluid)
 

1. What is fluid force at the end of a pipe?

The fluid force at the end of a pipe refers to the pressure exerted by a moving fluid against the end of a closed pipe. This force is caused by the fluid's momentum and can have both magnitude and direction.

2. How is fluid force at the end of a pipe calculated?

The fluid force at the end of a pipe can be calculated using the equation F = ρAv², where F is the force, ρ is the density of the fluid, A is the cross-sectional area of the pipe, and v is the velocity of the fluid. The direction of the force can be determined by the direction of the fluid flow.

3. What factors affect the fluid force at the end of a pipe?

The fluid force at the end of a pipe can be affected by various factors such as the velocity of the fluid, the density of the fluid, the cross-sectional area of the pipe, and the shape of the pipe. Other external factors such as obstacles or changes in the fluid's properties can also impact the force.

4. How does the fluid force at the end of a pipe impact the pipe itself?

The fluid force at the end of a pipe can have a significant impact on the pipe itself. If the force is too strong, it can cause the pipe to burst or deform. This is why it is important to consider the fluid force when designing pipes and other structures that come into contact with moving fluids.

5. Can the fluid force at the end of a pipe be controlled?

Yes, the fluid force at the end of a pipe can be controlled to some extent. By adjusting the properties of the fluid, such as its velocity or density, or by changing the shape of the pipe, the magnitude and direction of the force can be altered. Additionally, using certain materials or reinforcing techniques can help to better withstand the force and prevent damage to the pipe.

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