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Unformatted text preview: e problem of head loss in pipe flow. Functionally, we can assume that
w  v v where  F( , V, , d, ) is the wallroughness height. Then dimensional analysis tells us that eText Main Menu  Textbook Table of Contents  Study Guide (6.28) 340 Chapter 6 Viscous Flow in Ducts 8w
V2 f F Red, (6.29) d The dimensionless parameter f is called the Darcy friction factor, after Henry Darcy
(1803 – 1858), a French engineer whose pipeflow experiments in 1857 first established
the effect of roughness on pipe resistance.
Combining Eqs. (6.27) and (6.29), we obtain the desired expression for finding pipehead loss
hf f L V2
d 2g (6.30) This is the DarcyWeisbach equation, valid for duct flows of any cross section and for
laminar and turbulent flow. It was proposed by Julius Weisbach, a German professor
who in 1850 published the first modern textbook on hydrodynamics.
Our only remaining problem is to find the form of the function F in Eq. (6.29) and
plot it in the Moody chart of Fig. 6.13. Equations of Motion For eithe...
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 Spring '08
 Sakar

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