For laminar flow in rectangles and triangles the wall

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Unformatted text preview: yet to be achieved, although numerical models are improving [36]. e-Text Main Menu | Textbook Table of Contents | Study Guide 366 Chapter 6 Viscous Flow in Ducts Midplane Fig. 6.16 Illustration of secondary turbulent flow in noncircular ducts: (a) axial mean-velocity contours; (b) secondary-flow cellular motions. (After J. Nikuradse, dissertation, Göttingen, 1926.) (a) (b) EXAMPLE 6.15 Air, with 0.00237 slug/ft3 and 0.000157 ft2/s, is forced through a horizontal square 3 9-by 9-in duct 100 ft long at 25 ft /s. Find the pressure drop if 0.0003 ft. Solution Compute the mean velocity and hydraulic diameter V Dh From Table 6.4, for b/a 25 ft3/s (0.75 ft)2 4A 9 in 0.75 ft 1.0, the effective diameter is Deff whence Reeff From the Moody chart, read f ghf gf or 64 Dh 56.91 VDeff Deff p 4(81 in2) 36 in 44.4 ft/s 0.843 ft 44.4(0.843) 0.000157 0.0003 0.843 239,000 0.000356 0.0177. Then the pressure drop is L V2 Dh 2g 0.00237(32.2) 0.0177 p 100 44.42 0.75 2(32.2) 5.5 lbf/ft2 Ans. | v v Pressure drop in air ducts is usually...
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.

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