roughness pipe friction

roughness pipe friction - VD Reynolds number ll: - [37]-l...

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Unformatted text preview: VD Reynolds number ll: - [37]-l EFFECT OF SURFACE ROUGHNESS Table 11-10 Roughness of Commercial Pipes __________________’——-———-—-— Pipe Type e (roughness), in. ________________————————- Drawn tubing 6 X 10—5 Brass, lead, glass, spun cement 3 X 10" Commercial steel, wrought iron 1.8 X 10‘3 Cast iron (asphalt dipped) 4.8 X 10‘3 Galvanized iron 6 X 10’3 Wood stave 0.72—3.6 x 10—2 Cast iron (uncoated) 1.02 X 10'2 Concrete 1.2-«12 X 10'2 Riveted steel 3.6{36 X 10—2 —_——__——_———————'——l——-—— 493 [36] glued uniformly sized sand grains as close together as possible on the inside of round pipes and made extensive measurements. Measurements on pipes with commercial roughnesses are summarized by Moody [37] in the Moody diagram in Fig. 11-6. The average height of a roughness element is denoted by e, some typical values of which are given in Table 11-10, but it is seen in Fig. 11-6 that the relative roughness e/D [is of greatest significance. Thus a small-diameter pipe can be relatively rougher than a large-diameter pipe even though both are manufactured by the same process and from the same material. For commercially rough pipes the correlation of Colebrook [38] 71-72- — 1.74 210810(2D + ReDfl/Z) can be used in the turbulent range. For sand-roughened pipes the correlation given by Nedderman and Shearer [39] 1 _- e 28.3 —f1—/5 -— 1.74 210g10(2D EeDfl/Z) with Re D (e / D )( f / 8)‘/ 2 > 12 is required since commercial roughness does not Show the dip in the transition region exhibited by sand roughnesses. An easily programmable relationship between the friction factor f for pressure drop is given by Round [82] for turbulent flow as 1 —1810 ——————1—-————‘ .fI/z“ ' g“) 0.135e/D+6.5/ReD: ),- 4OOOSReD Another such relationship valid for both laminar and turbulent flow is given 7 muuinol aman 0.”.05 mm s Reynolds 684 (1944) II I IIIII IIII “I !!L!!!! tIIlllll ‘ A Illllllllllll --H---- I _. .-M-r~.«-._ Innu- II )A p for pipe flow versu Transact. ASME 66, 671- 2 v a U A A Reynolds number it: -A 1.2 A ll== ll'l-YII un ‘lfllllth/l Illlmummm lllllllllllWMllm llllllll Imull Il'nllllll. IIIEII lillll UavD/v. [From L. F. Moody, . ,, 19,41 Ill-AI’I'I‘III- In W -6 Friction factor f = (D / L)(2/ p I- -'-l lrl$:\\\V\\\XS'. .\\\\Is\\\“ ‘ @- number Re D [371-] Figure 11 EFFECT OF SURFACE ROUi Table 11-10 i Pipe Type ______.J Drawn tubin Brass, lead, g Commercial Cast iron (as Galvanized i Wood stave Cast iron (ui Concrete Riveted stee [36] glued uniformly si inside of round pipes . pipes with commercial Moody diagram in Fi denoted by e, some ty seen in Fig. 11-6 that Thus a small-diameter I pipe even though both same material. For com with ReD (e/D)(f/8)l show the dip in the tr An easily progr pressure drop is given 1 fl/Z = 1.81 Another such rel atior‘ ...
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roughness pipe friction - VD Reynolds number ll: - [37]-l...

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