PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.A.2 Hydraulic designThe pressure (∆h) drop in a pipeline can generally be described by the formula :22L v v ∆ρ∆ h = f ⋅ + k ⋅ + ⋅ yD 2 ⋅ g∑A.2-1)2 ⋅ g ρof = coefficient of friction (see diagram fig. A.2.1.1)L = length of pipe (m)D = internal diameter (m)v = velocity in pipe (m/s)g = acceleration of gravity (= 9.81 m/s 2 )Σk = sum of coefficients for singular head losses∆ρ = density difference between water inside the pipe and water in recipient (kg/m 3 )ρ o = density of water inside the pipe (kg/m 3 )y = water depth at outlet point in recipientA.2.1Coefficient of frictionThe friction coefficient (f) is dependent of Reynolds number (R e ) :v = velocityD = internal diameter (m)ν = viscosity of water (m 2 /s)The viscosity of water depends on the temperature.T = 20ºC ν = 1.0 ⋅ 10 –6 m 2 /sT = 10ºC ν = 1.3 ⋅ 10 –6 m 2 /sWe recommend applying the value for 10ºC.v ⋅ DR e =A.2-2)νThe velocity (v) can be calculated by the formula :Q = flow (m 3 /s)4 ⋅ Qv = A.2-3)2πDAs we see, the Reynolds number can be calculated if we know the flow and the internal diameter.Example 1Destine Reynolds number for a flow of 100 l/s in a pipe with internal diameter 327.2 mm. T = 10ºCSolution :First we calculate the velocity, v, from A.2-3)Reynolds number is found from A.2-2)4 ⋅ 0,100v =π ⋅ 0,32722m / s= 1,19 m / s1,19 ⋅ 0,3272R e == 2,09⋅10−61,31⋅105When we know the Reynolds number, the friction coefficient can be found from the Moody chart, fig.A.2.1.1.Side 18 av 84