Discussion: “Predicting the Colebrook–White Friction Factor in the Pipe Flow by New Explicit Correlations” (Azizi, N., Homayoon, R., and Hojjati, R. M., 2018, ASME J. Fluids Eng., 141(5), p. 051201)

Abstract

The present comment concerns some doubtful results included in the discussed paper. [DOI: 10.1115/1.4045614]The discussed publication [1] proposes two new explicit approximations of the Colebrook–White equation (CWE) [2], which is commonly used to estimate the Darcy–Weisbach friction factor for turbulent flows. While appreciating the work of the authors, the writer noticed issues that deserve attention.Equations proposed to substitute the CWE should consider multiple evaluation criteria, such as formula accuracy, computational efficiency, and compactness. The relative importance of these criteria depends on the intended use. For example, for manual calculations compactness (simplicity) is very important, accuracy is desirable, while computational efficiency has little meaning. Manual calculations are typical for introductory fluid mechanics/hydraulics courses (involving a large user base) because the use of programable calculators and computers is often prohibited.