PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.0,25Hence : r r = = 0,0008327,2Knowing R e and r r we take f from fig. A.2.1.1 as indicated in the diagram with dotted lines andarrows.The result is : f ≈ 0.02For rough estimates without any Moody chart in hand, it is often usual to use f = 0.02 as an averagevalue.Knowing f, we can calculate the friction pressure drop (∆h f ) for the pipeline from part one informula A.2-1)2L v∆ h f = f ⋅ ⋅A.2-5)D 2 ⋅ gExample 3Calculate the friction pressure drop for the pipeline described in example 1 and 2 if the lengthis 2500 m.Solution :Formula A.2-5) gives the result in the unit mwc (meter water column) :∆ h2f =2500 1,19= 0,02 ⋅ ⋅ mwc0,3272 2 ⋅ 9,8111,03 mwcTo convert this unit to Pa (N/m 2 ) we introduce the relationship :p = ρ ⋅ g ⋅ h A.2-6)p = pressure (N/m 2 = Pa)ρ = density of water (1000 kg/m 3 )g = acceleration of gravity (9.81 m/s 2 )This gives : p = 1000 ⋅ 9.81⋅ 11.03 Pa = 108204 PaIf we divide this figure with 10 5 we get the unit (bar), and if we divide it with 10 6 we havethe unit Mpa.108204108204p = bar = 1.08 barp = MPa = 0.108 MPa1000001000000A.2.2Coefficient for singular head lossesPart two of formula A.2-1) represent the singular pressure drops (∆h s ) :2v∆hs = ∑ k ⋅A.2-7)2 ⋅ gThe expression Σk means a sum of discrete head losses.Head losses arise for instance in bends, in diameter changes, in inlet and outlet of pipe, in beads,in valves, in screens, in water meters and in diffusers.Side 20 av 84