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  eText 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 effectivelaminardiameter idea collapses all data for rectangular ducts of arbitrary heighttowidth 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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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.
 Spring '08
 Sakar

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