Contributed by the Fluids Engineering Division of THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS. Manuscript received by the Fluids Engineering Division September 14, 2000; revised manuscript received February 9, 2001. Associate Editor: D. R. Williams.

Many researchers have investigated the Fanning factors in circular ducts and proposed many correlating equations to calculate the Fanning factors. As to various noncircular ducts, the frictional pressure drops have rarely been investigated. So it has been common practice in the field of fluid mechanics to use the hydraulic or equivalent diameter in the Reynolds number in predicting turbulent pressure drops along duct lengths having noncircular cross section.

But, there is usually large deviation from the circular tube line by using the hydraulic diameter in the Reynolds number. And, therefore, some researchers have proposed various modifying methods to predict friction factors. In the case of rectangular ducts, for example, Jones...

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