How to calculate the wetted perimeter

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SUMMARY

The wetted perimeter is defined as the perimeter in contact with the fluid, which is crucial for calculating flow characteristics in fluid dynamics. In the context of internal forced convection in a thick-walled pipe, the correct wetted perimeter is not simply 2πr, where r is the inner radius. Instead, for axial flow in an annular channel formed by two concentric cylinders, the wetted perimeter must account for both the inner and outer surfaces of the annulus, leading to a different calculation.

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  • Understanding of fluid dynamics principles
  • Familiarity with annular flow concepts
  • Knowledge of cylindrical geometry
  • Basic calculus for perimeter calculations
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theBEAST
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So I have been taught that the wetted perimeter is the perimeter in which the surface is wet. So in the case for internal forced convection of a thick wall pipe I would have thought the perimeter would be 2*pi*r where r is the inner radius of the pipe. However, doing a bit of googling, this answer is clearly wrong as shown in the image below:
zyObkrl.png


Does anyone know why?
 
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Yes. This is not a thick walled pipe calculation. It is a calculation of axial flow along an annular channel (between two concentric cylinders).

Chet
 

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