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Journal of Enhanced Heat Transfer
Facteur d'impact: 0.562 Facteur d'impact sur 5 ans: 0.605 SJR: 0.211 SNIP: 0.361 CiteScore™: 0.33

ISSN Imprimer: 1065-5131
ISSN En ligne: 1026-5511

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Journal of Enhanced Heat Transfer

DOI: 10.1615/JEnhHeatTransf.v1.i1.50
pages 53-64

Influence of Roughness Shape and Spacing on the Performance of Three-Dimensional Helically Dimpled Tubes

Thomas J. Rabas
Energy Systems Division, Argonne National Laboratory, Argonne, IL USA 60439-4815; Consultant, 1015 Claremont Drive. Downers Grove, IL 60516
Ralph L. Webb
Department of Mechanical Engineering The Pennsylvania State University, University Park, PA 16802, USA
Specialist in enhanced heat transfer and heat exchanger design
Petur Thors
Wolverine Tube, Inc., 2100 Market Street N.E., Decatur, Alabama 35602, USA
N.-K. Kim
Kum-Oh National Institute of Technology, Kumi-City Kyungbuk-Korea


A comparison of measured and predicted heat-transfer and friction-factor values is first presented for two newly developed doubly enhanced tubes. The internal enhancement consists of three-dimensional roughness elements that are essentially spherical segments and are formed by externally dimpling the outside surface. Very good agreement was obtained with these experimental data and the heat-transfer and friction-factor values obtained with prediction methods developed by Taylor and Hodge (1992a, 1992b) for three-dimensional roughened tubes. These prediction methods were then used to determine the variations of the inside heat-transfer enhancement level and the efficiency index (heat-transfer enhancement divided by the friction-factor increase) for different spherical shapes and spacings. This analysis revealed the following: significant performance improvements are possible with a greater roughness curvature and closer roughness spacings. The maximum enhancement level and efficiency-index value of 3.5 and 1.7, respectively, were obtained for water with touching half-spheres. These predicted values exceed all previously published values for passive enhancement geometries. However, these values are obtained for roughness geometries that are very different from those used for validation of the prediction algorithms developed by Taylor and Hodge (1992a, 1992b).

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