Chapt06

75 80 pressure drop p lbfft2 60 40 laminar flow p v 20

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Unformatted text preview: 40 Laminar flow ∆p α V 20 Transition | v v Fig. 6.4 Experimental evidence of transition for water flow in a 1 -in 4 smooth pipe 10 ft long. | 0 0 e-Text Main Menu 0.5 | 1.0 1.5 Average velocity V, ft/s Textbook Table of Contents 2.0 | 2.5 Study Guide 330 Chapter 6 Viscous Flow in Ducts streak into a pipe flow, Reynolds could observe transition and turbulence. His sketches of the flow behavior are shown in Fig. 6.5. If we examine Hagen’s data and compute the Reynolds number at V 1.1 ft/s, we obtain Red 2100. The flow became fully turbulent, V 2.2 ft/s, at Red 4200. The accepted design value for pipe-flow transition is now taken to be Dye filament Needle Tank (a) Red,crit 2300 (6.2) This is accurate for commercial pipes (Fig. 6.13), although with special care in providing a rounded entrance, smooth walls, and a steady inlet stream, Red,crit can be delayed until much higher values. Transition also occurs in external flows around bodies such as the sphere and cylinder in Fig. 5.3. Ludwig Prandtl, a German engineering professor, showed in 1914 that the thin boundary layer surrounding the body was undergoin...
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