Comparison of Pipe Friction Factor Formulas

Since Chezy's mean-velocity equation was published. many researchers have tried to compute friction coefficient using the modified form of Chezy equation. But as the empirical parameters used in the equations are not clearly defined because they depends on engineer's experience and it is considerably difficult to estimate them accurately. serious mis-understandings may have been drawn in the computation of pipe friction factor Because of these reasons. the present study clarifys the limit and problems of the empirical equations by the comparison of these pipe friction coefficients, and it offers a guide line in the use of pipe friction factor equations and discusses the difference and similarity of friction factor equations of composite surface which Yoo (1995) and Barr (1975) proposed. On the other hand. this study re-analyzed the experimental data of Colebrook (1938) to estimate the equivalent roughness height and probability and confirmed the validation of two methods : mean zero velocity point and mean friction factor.