Deriving Velocity Profiles for Flow of Oil Down Glass Rod

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SUMMARY

The discussion focuses on deriving velocity profiles for the flow of oil down a vertical glass rod, specifically with oil density at 900 kg/m³ and viscosity at 120 mPa·s. The key steps include utilizing the Navier-Stokes equations in cylindrical coordinates while making assumptions such as steady, two-dimensional flow in the r-z plane, gravitational force driving the flow, negligible shear forces at the oil-air interface, and zero velocity components in the r and θ directions. Integration of the equations is necessary to complete the derivation.

PREREQUISITES
  • Understanding of Navier-Stokes equations in fluid dynamics
  • Familiarity with cylindrical coordinate systems
  • Knowledge of fluid properties such as density and viscosity
  • Basic calculus for integration techniques
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Fluid dynamics students, mechanical engineers, and researchers working on oil flow problems or similar fluid behavior in cylindrical geometries.

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I am having a huge problem with understanding the derivation of velocity profiles for these type of problems. The one i am having the most difficulty is the flow of oil going down vertically along the surface of a glass rod. Where p=900 kg/m^3 and u=120 mPa's. How do I start this problem?
 
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here is the key

Start by writing Navier-stokes equations in cylindrical coordinates.And make reasonable assumptions to simplify the equations. Like, 1 The flow is steady and two dimensional in r-z plane. Here z is the coordinate pointing downwards.You can also chose it to be pointing upwards. In both cases you should pay attention to the signs in the equations. 2 The flow is driven by gravational forces. 3 The shear forces on interface of oil and air are negligible. 4 The flow is in only z direction. Thus the r and θ velocities component go to zero.
Now you need to do some integrations. I am leaving the rest to you...
Good luck!
 

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