Chapt06

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Unformatted text preview: Flow in Noncircular Ducts 357 EXAMPLE 6.12 Work Moody’s problem, Example 6.6, backward to find the unknown (6 in) diameter if the flow rate Q 1.18 ft3/s is known. Recall L 200 ft, 0.0004 ft, and 1.1 E-5 ft2/s. Solution Write f, Red, and /d in terms of the diameter: gh f d 5 8 LQ2 (32.2 ft/s2)(4.5 ft)d5 8 (200 ft)(1.18 ft3/s)2 2 f 2 0.642d 5 4(1.18 ft3/s) (1.1 E-5 ft2/s) d Red d or d 1.093 f 1/5 136,600 d (1) (2) 0.0004 ft d (3) with everything in BG units, of course. Guess f ; compute d from (1), Red from (2), and /d from (3); and then compute a better f from the Moody chart. Repeat until convergence. The writer traditionally guesses an initial f 0.03: Table 6.2 Nominal and Actual Sizes of Schedule 40 WroughtSteel Pipe* Nominal size, in f 0.03 0.269 0.364 0.493 0.622 0.824 1.049 1.610 2.067 2.469 3.068 *Nominal size within 1 percent for 4 in or larger. 1.093(0.03)1/5 Red 136,600 0.542 252,000 fnew 0.0196 dnew Actual ID, in 11 8 11 4 13 8 11 2 13 4 13 4 11 2 23 4 21 2 33 4 d fbetter 0.0198 d 0.542 ft d 7.38 E-4 0.498...
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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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