Since flow data is usually given in gallons per minute and pipe

diameters in inches, it is more convenient to express the Darcy

Weisbach equation as:

Where:

Hf = friction head loss, in ft

f = dimensionless friction factor based on the Rn and the inside

roughness of pipe

L = length of pipe, in ft

Q = flow, in GPM

d = inside diameter of the pipe, in inches

0.031 = Constant

Hf = 0.031xfLxQ,,

d5

Example: Calculate frictional head loss, given the following information

and using the following equation.

Pipe size = 8.415 inches.

Fuel = DF-2 at 50F.

V = 4 ft/sec

Length of pipe = 4000 ft.

Hf = fxLxV,,

2gxD

Calculate Reynolds number

K = 4.9 = 0.0000527

Y = 92900

R = VD = 4 x .701 = 53206.8317(52307) or 5.3 x 10

.0000527

R = 3.160 xQ

dxK

To obtain Kinematic viscosity in centistokes, use Figure 1-1; move up the

scale to DF-2, move to the left and read 4.9.

Locate 5.36 x 10, move up the chart to 8 inch pipe, move to the left and

read .0216 or .022.

Hf = fxLxV,,

2gxD

2g = 2x32.2 = 64.4

Diameter of pipe in ft. = .701

Hf = .0216x4000x16 = 1382.4

64.4 x .701

45.14

12-14

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