A new explicit equation for accurate friction factor calculation of smooth pipes

Calculation of friction factor for smooth pipes in fully developed flow is important for heat transfer applications. Many different coefficients in the Prandtl equation (Prandtl, L., 1949. Führer durch die Strömungslehre. F. Vieweg & S, Braunschweig.), or PKN correlation [Kakac, S., Shah, R.K., Aung, W., 1987. Handbook of Single-Phase Convective Heat Transfer. John Wiley & Sons; Rohsenow, W.M., Hartnett, J.P., Cho, Y.I., 1998. Handbook of Heat Transfer. McGraw-Hill Professional.], are cited in the literature. This report reviews these coefficients and presents the original Prandtl equation based on the Fanning friction factor. In addition, a new explicit equation is presented to approximate the PKN correlation. This equation yields a more accurate approximation than the existing ones.