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Fully developed turbulent flow through three concentric annuli was investigated experimentally for a Reynolds-number rangeRe= 2 × 104−2 × 105. Measurements were made of the pressure drop, the positions of zero shear stress and maximum velocity, and the velocity distribution in annuli of radius ratios α = 0.02, 0.04 and 0.1, respectively. The results for the key problem in the flow through annuli, the position of zero shear stress, showed that this position is not coincident with the position of maximum velocity. Furthermore, the investigation showed the strong influence of spacers on the velocity and shear-stress distributions. The numerous theoretical and experimental results in the literature which are based on the coincidence of the positions of zero shear stress and maximum velocity are not in agreement with reality.

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Abstract-On the basis of friction factor relationships of a simple model a method is developed which allows the prediction of friction factors for turbulent flow in non-circular channels if only the geometry factor of the pressure drop relationship for laminar flow is known. The proposed method of calculation is tested with numerous experimental results from the literature with respect to non-circular channels such as triangular shaped ducts, eccentric annuli and rod bundles in hexagonal and square arrays in circular tubes, hexagonal and square channels. It turns out that the proposed method provides an excellent description of all the experimental data at hand.channel wall and rods; annular zone parameter; wall distance; dimensionless wall distance y+ =