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Calculating Friction Loss for Column Pipe When a Line Shaft is Present

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  131594356,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: http://dx.doi.org/10.13031/aim.20131594356) @2013
Authors:   Joseph C. Henggeler, Allen L. Thompson
Keywords:   Manning Equation annulus n value

Abstract. Because of the presence of a lineshaft inside of it, column pipe flow represents flow of an annulus. Effective cross-sectional area, wetted perimeter, and hydraulic radius differ from that of regular pipe of the same diameter. The Manning equation, which uses all of those parameters, was used to calculate Hf for various combinations of column pipe/lineshaft size. The results of each column pipe/lineshaft configuration were graphed alongside of regressed curves from charts for the same configuration. The Manning friction factor, n, was manipulated until the Manning curve best described the regressed chart curve. This then was the best fit n value for that combination. Twenty-nine separate combinations were so treated.

The average n value was 0.012 and ranged from 0.010 to 0.020 (regular steel pipe is 0.014). Generally, the n value decreased with larger size column pipe. The parameter that best described the fluctuating nature of n was diameter of column pipe/diameter of line shaft (D/d). When n was correlated to D/d for large (20-24 inch), medium (10-18 inch), and small (3-10 inch) column pipe the R2 was 0.92, 0.30, and 0.79, respectively. The study showed that the Manning equation can accurately predict Hf in column pipe and that its accuracy will be enhanced by adjusting n using D/d in a quadratic equation describing n. The parameters for the adjusting equation differ based on general column pipe size (small, medium, or large).

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