Turbulent newtonian flow in annuli

In recent years there have been quite a few experimental studies on turbulent flow in annuli. In this paper a Prandtl mixing‐length approach is applied to give a friction factor vs. Reynolds number expression for annuli [see Equation (22) and Table 1]; this expression describes tube flow and slit flow as special cases. No new adjustable constants appear in the final result other than those determined earlier for tube flow. The final expression is found to predict friction factors within the accuracy of the existing experimental data. The mixing‐length friction‐factor expression is thus substantially more accurate than the usual hydraulic‐radius procedure and of comparable accuracy to other recent annulus friction‐factor treatments.