Prediction of wall friction factor in horizontal annular flow using the asymptotic method

Highlights: • Prediction of wall friction factor in horizontal annular flow using the asymptotic method is presented. • The asymptotic method is simple, explicit and has only one unknown parameter (the fitting or "blending" parameter (n)). • Comparison of the asymptotic model with the solution available in the literature is presented. - Abstract: In this study, wall friction factor (fw) in horizontal annular flow is predicted using the asymptotic method. There are two asymptotes for wall friction factor (fw) in horizontal annular flow. The first asymptote corresponds to small value of liquid Reynolds number (Rel) in laminar flow. The second asymptote corresponds to high value of liquid Reynolds number (Rel) in turbulent flow. Using the methods discussed by Churchill and Usagi (1972), the fitting parameter in the proposed model can be determined. The asymptotic solution agrees well with the integral analysis in both laminar and turbulent flow and has the additional advantage of including the "transition" region. Comparison of the asymptotic model with the solution available in the literature is presented