Water Skin Effect in Plastic Pipe

[DeereAdam]

I need to Calculate the Skin Effect of water in a tube of X Diameter or Surface Area... The length of the Flow in the pipe would be 200 mm. I know that is short but it matters in this instance. The pressure of the water would be around 15 bar. I will post the flow rate through the pipe as soon as possible. The Diameter of the tube will change so I am looking for a calculation that I can input the flow rate and diameter and output the force from skin effect. The pipe is very smooth something similar to pvc. thanks for the help

 

[anorlunda]

ping @jrmichler

 

[jrmichler]

I think the OP is asking about friction stress between the fluid and the tube wall. Fluid enters a pipe with equal velocity across the pipe entrance. Friction between the fluid and pipe changes the velocity profile to parabolic if the flow is laminar, and to a more complex velocity profile if the flow is turbulent. That transition occurs over a length of (typically) 10 to 20 tube diameters. Or more, or less, depending.

A 200 mm long tube is a short tube if the tube diameter of 10 to 20 mm or more. The flow in the entire length of the tube will be in transition from the flat velocity profile at the entrance to the fully developed velocity profile. Search fluid flow entrance length for procedures and equations. Note that laminar and turbulent flow are handled differently.

If a 200 mm long tube is, say 2 mm diameter or less, the entrance length will be a small fraction of the tube length. Then it can be analyzed as if the entire length is fully developed flow with minor error. Search Moody chart for the friction factor, the equation, and how to use the equation. This chart works for both laminar and turbulent flow.

Tube diameter between these ranges are a challenge, mostly because of the difficulty in accurately calculating the entrance length. You need to calculate the entrance length. Friction in the entrance length and friction in the fully developed flow are calculated separately.