Rotating Cylinder - Understanding Gas Pressure and Density

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SUMMARY

The discussion focuses on calculating gas pressure and density within a rotating cylindrical container. The user is investigating two scenarios: a sealed cylinder with a fixed volume of gas and a cylinder with a hole at the axis allowing gas flow. Key parameters include a cylinder volume of 1 liter, a radius of 0.05 meters, and a rotational speed of 2000 RPM. The user seeks to adapt the formula P = dmw²r² for gas pressure calculations, considering the effects of centripetal force and varying density across the cylinder's radius.

PREREQUISITES
  • Understanding of centripetal force and its effects on gas behavior
  • Familiarity with gas laws and pressure calculations
  • Knowledge of rotational dynamics and fluid mechanics
  • Experience with mathematical modeling in physics
NEXT STEPS
  • Research the application of the ideal gas law in non-constant gravitational fields
  • Explore the effects of rotational speed on gas density distribution
  • Learn about fluid dynamics in rotating systems
  • Investigate the implications of vacuum conditions on gas pressure calculations
USEFUL FOR

This discussion is beneficial for engineers, physicists, and researchers involved in fluid dynamics, particularly those working with rotating systems and gas behavior under varying pressure conditions.

Johnsson
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Hi,

I have a cylindrical container of gas that is rotating about the axis (of symmetry).
I'm trying to understand and calculate what is happening to the atmosphere inside.

Obviously, as the cylinder accelerates up to speed, the gas will also accelerate and eventually get to the same speed as the container (I have baffles to help this) and the gas will be more compressed/dense against the inside surface and less dense at the axis.

I'm wanting to get some idea of the pressure and density of the air at various points (inside surface and axis).
I can't use standard formulas that relate to a constant gravity/density (Pres.=Density x g x height) due to the fact that the artificial gravity/centripetal force created by the rotation is not constant across the radius of the cylinder and therefore the density also changes.The two scenarios I am looking at are -

1) a sealed cylinder i.e. fixed volume of gas - Is there any effect on the calculation if the rotational speed is such that the axis is under vacuum?

2) a cylinder with a hole at the axis i.e. gas can flow into cylinder as it accelerates up to speed. - I guess we can assume that gas pressure at the axis is constant at 1 atmosphere (ambient)

rough parameters I'm working with are
Cylinder volume - 1 litre
Cylinder radius - 0.05m
Rot speed - 2000 rpm
Air is at standard room temp and pressure
 
Last edited:
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how about if I substitute F=mw^2r into the P=dgh formula.

P=dmw^2r^2

Can I use this for gas pressure calculation in this case.

Please not this is not a hypothetical question or an academic problem but rather a scenario in our work environment.
 

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