Pipe Flow/Friction Factor Calculations II: ( S.I. units )

Calculation of pipe diameter, D, for given flow rate, Q, pipe length, L,

(NOTE: This is an iterative calculation. An assumed value of D will be used to start.)

Inputs Calculations

6 m 80 mm

0.15 mm 0.0800 m

30 m 0.02300

0.017 0.0050

1000 3.4 m/s

0.0013 208,005

2. Check on whether the given flow is "completely turbulent flow"

(Calculate f with the transition region equation and see if differs from the one calculated above.)

Transistion Region Friction Factor, f: f = 0.0239

Repeat calc of f using new value of f: f = 0.0239

pipe roughness, e, head loss, hL, and fluid properties, r & m.

1. Determine Friction Factor, f, assuming completely turbulent flow [ f = 1.14 + 2 log10(D/e)-2 ]

Allowable Head Loss, hL = Assumed Pipe Diam, D* =

Pipe Roughness, e = Pipe Diameter, D =

Pipe Length, L = Friction Factor, f =

Pipe Flow Rate, Q = m3/s Cross-Sect. Area, A = m2

Fluid Density, r = kg/m3 Ave. Velocity, V =

Fluid Viscosity, m = N-s/m2 Reynolds number, Re =

[ f = {-2*log10[((e/D)/3.7)+(2.51/(Re*(f1/2))]}-2 ]

Repeat again if necessary: f = 0.0239

3. Calculate pipe diameter, D using the final value for f calculated in step 2

0.070 m = 70 mm

NOTE: This iterative procedure doesn't converge smoothly to a solution. If the calculated pipe diameter

in this step is larger than the assumed pipe diameter above, then replace the assumed pipe diameter

value with the next larger standard pipe size. Repeat until you find the smallest standard pipe diameter

that gives a smaller calculated required pipe diameter. That is your solution.

With the example values given here, an assumed pipe diameter of 65 mm gives a calculated pipe

diameter requirement of 167 mm, increasing the assumed pipe diameter to the next standard pipe size

( 80 mm ) gives a calculated pipe diameter requirement of 70 mm, so an 80 mm size is the minimum

standard pipe diameter that will do the job.

*Standard pipe diameters in mm:

6, 8, 10, 15, 20, 25, 32, 40, 50, 65, 80, 90, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500, 600, 750,

900, 1050, 1200, 1350, 1750, 1600, 1700, 1800, 1900, 2000

[ D = f(L/hL)(V2/2g) ]

Pipe Diameter, D =