The Alaska pipeline is a 4 feet (1.22m) in diameter. Crude oil (S.G. = 0.90) flo

Question

The Alaska pipeline is a 4 feet (1.22m) in diameter. Crude oil (S.G. = 0.90) flows through it at a rate of 3.3 m^3/s. The viscosity of the oil is very temperature dependent but appears to be around n = 10 mPa s. The inlet to the pipe is at an elevation of 45m and the pressure at the inlet is 8.25 MPa. At the outlet, the pressure is 350 kPa (gauge) with an elevation of 115 m. (a) Calculate the approximate Reynolds number in the pipe, (b) Calculate the head loss in this section of the pipe, (c) What percentage of the pressure drop is due friction?

Explanation / Answer

Answer (a)

Calculate Reynolds number in the pipe.

Here Q = 3.3 m3/s = v x A =v x 0.785 x d2

v = (3.3 m3/s ) / (0.785 x (1.22 m)2)

v = 2.82 m/s

Now Reynold number Re = Dv / = ( 1.22 m x 2.82 m/s x 900 kg/m3) / (0.01 kg/ms )

                                   Re = 309636 so the flow is turbulant

(b)

Total suction head calculation

1. The suction side of the system shows a minimum static head of 147.6 feet (45 m) above suction centerline. Therefore, the static suction head is:

hss = 147.6 feet

2. Using the first conversion formula, the suction surface pressure is:

hps = -20 Hg x 1.133/ 0.900 = -23.17 feet gauge

3. The suction friction head, hfs, equals the sum of all the friction losses in the suction line. Friction loss in 6" pipe at 1000 gpm from table 15 of the Hydraulic Institute Engineering Data Book, is 6.17 feet per 100 feet of pipe.

in 4 feet of pipe friction loss = 4/100 x 6.17 = 0.3 feet

The total suction head then becomes:

hs = hss + hps - hfs = 147.6 + (-23.12) - 0.3 = 124.18 feet, gauge at 1000 gpm.

so for 15306 gpm ( 3.3 m3/s) = (15306/1000) x 124.18 = 1900 feet

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