Calculating the force air has on an object

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Discussion Overview

The discussion revolves around calculating the force exerted by compressed air on bottles being transported along a production line. Participants explore different approaches to determine this force, considering factors such as air velocity, pressure, and the area of contact between the air and the bottles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests using the equation of quantity of motion (F=rho*Q*deltaV) to calculate the force, noting that they have not observed a change in air speed along the trajectory.
  • Another participant questions how compressed air applies force to the bottles, specifically asking about the area of application and confirming that the air pushes from the base of the bottles.
  • A clarification is made that the bottles are transported through guides and propelled by air flowing around their tips, with a need to calculate the horizontal force exerted by the air.
  • One participant proposes calculating the fall in pressure of the compressed air as it exits the compressor, suggesting that this pressure drop can be used to determine the force acting on the bottles based on pressure and area.
  • Another participant explains that the force can be calculated as pressure times area, referencing Bernoulli's equation to relate total pressure, static pressure, and dynamic pressure, while noting the conditions under which this applies.
  • One participant suggests using the drag equation as an alternative approach, indicating that the bottles are pushed by an air current.

Areas of Agreement / Disagreement

Participants express various viewpoints on how to approach the calculation of force, with no consensus reached on a single method. Some propose using Bernoulli's equation, while others suggest the drag equation, indicating a lack of agreement on the best approach.

Contextual Notes

Participants mention different sources of air (compressor vs. storage tank) and the conditions under which the equations may apply, highlighting the complexity of the scenario and the need for clarity on definitions and assumptions.

krlss26
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I am trying to calculate the force that compressed air has on a cylinder.

These cylinders are pushed in a production line for transportation using air. I would like to calculate the force such air puts on the cylinder.

I have the velocity of the air, the área of the cylinder.

Will using the equation of quantity of motion (F=rho*Q*deltaV) work? I have not seem to find a difference in the speed of air in any part of the trajectory.

Please, help, and thank you for your time.
 
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krlss26 said:
I am trying to calculate the force that compressed air has on a cylinder.

These cylinders are pushed in a production line for transportation using air. I would like to calculate the force such air puts on the cylinder.

I have the velocity of the air, the área of the cylinder.

Will using the equation of quantity of motion (F=rho*Q*deltaV) work? I have not seem to find a difference in the speed of air in any part of the trajectory.

Please, help, and thank you for your time.
Exactly how does the compressed air apply a force on the cylinder? As in on which area? If I understood right, the cylinders are pushed in by the air, so the air would have to act on the base of the cylinder
 
siddharth23 said:
Exactly how does the compressed air apply a force on the cylinder? As in on which area? If I understood right, the cylinders are pushed in by the air, so the air would have to act on the base of the cylinder

They are actually bottles, that are transpoted from one area to another through guides and propulsed by air. Air flows around the tip of these bottles and it pushes them forward. I need to calculate the force that air, which comes horizontally and pushes them horizontally too. There are guides that avoid that these bottles fall.
 
krlss26 said:
They are actually bottles, that are transpoted from one area to another through guides and propulsed by air. Air flows around the tip of these bottles and it pushes them forward. I need to calculate the force that air, which comes horizontally and pushes them horizontally too. There are guides that avoid that these bottles fall.
Ok. I'm not too sure, but as I see it, the pressure energy of the compressed air will be converted to kinetic energy when the air comes out of the storage tank. This will lead to a fall in pressure, which will depend on the velocity. Calculate the fall in pressure an in turn, the pressure acting on the bottles. Knowing the pressure and area, you will get the force.
 
siddharth23 said:
Ok. I'm not too sure, but as I see it, the pressure energy of the compressed air will be converted to kinetic energy when the air comes out of the storage tank. This will lead to a fall in pressure, which will depend on the velocity. Calculate the fall in pressure an in turn, the pressure acting on the bottles. Knowing the pressure and area, you will get the force.

I am sorry if I did not explain myself very well. I am not a native English speaker.

The air does not come from a storage tank. It comes from a compressor which sends air through some vanes. The air flows along a guide and through that guide, cylinders travel. They are pushed by air that flows from the walls of this guide. I can determine the velocity of such air, and I have the área of the cylinder that is in touch with the air.
 
The force you can get is the pressure times the area.

Your compressor can produce a known maximum total pressure P0 (for example, when you are filling tank). Total means that the velocity is zero.

If that fluid starts moving at a certain velocity v, the pressure will drop to a value P. According to Bernoulli's equation, the following relation will be true:

P0 = P +½ρv²

Where ρ is the density of the fluid.

What you need to find out is that total pressure P0 and multiply this value by the area to find out the force. This will represents the effect of the static pressure (P) plus the effect of the dynamic pressure (½ρv²).

The previous equation can be used with compressible fluid as long as the velocity is below Mach 0.3. Otherwise, the compression of the fluid has to be considered.

More info on Wikipedia.
 
Thank you, guys. You have been really helpful.
 

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