What does resistance of a fluid flow depend on?

1 Answer
May 27, 2018

see below

Explanation:

the resistences to the flow of a fluid can be continuous or localized.
Continuous resistence are due by the viscosity of the same fluid, by the rugosity of the pipe, by the geometry of pipe, and by the velocity of the fluid in the pipe.

one possible relationship is:
R= f xx (L+L_(eq))/d xx v^2/2gR=f×L+Leqd×v22g
where
-L is the lenght of the pipe,
-d is its diameter,
-Leq is the equivalent Lenght, a factor that considers all the obstacles to the movement as curves, narrowings, enlargements, valves (opened or partially closed) and so on.
-v is the velocity
-g is the gravity acceleration (so R is in meters)

viscosity is hidden in the friction coefficient f that is determined in function of Reynolds adimensional number (Re) according with the attached Moody's diagram
Re= (d xx rho xx v)/muRe=d×ρ×vμ
Where:
d is the diameter
rhoρ the fluid density
muμ the fluid viscosity
v the velocity
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