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Unformatted text preview: ulent friction is predicted most accurately when we use an effective diameter Deff equal to 0.64 times the hydraulic diameter. The effect on f itself is much less, about 10 percent at most. We can compare with Eq. (6.83) for laminar flow, which predicted 64 2 Parallel plates: Deff Dh Dh (6.88) 96 3 This close resemblance (0.64Dh versus 0.667Dh) occurs so often in noncircular duct flow that we take it to be a general rule for computing turbulent friction in ducts: Deff | v v 360 | e-Text Main Menu | Dh 4A reasonable accuracy Textbook Table of Contents | Study Guide 6.6 Flow in Noncircular Ducts Deff(laminar theory) extreme accuracy 361 (6.89) Jones [10] shows that the effective-laminar-diameter idea collapses all data for rectangular ducts of arbitrary height-to-width ratio onto the Moody chart for pipe flow. We recommend this idea for all noncircular ducts. EXAMPLE 6.13 Fluid flows at an average velocity of 6 ft/s between horizontal parallel plates a distance of 2.4 in apart. Find the head loss and pressure drop for each 100 ft of...
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