Heat transfer and friction in tubes with repeated-rib roughness

Heat transfer and friction correlations are developed for turbulent flow in tubes having a repeated-rib roughness. The friction correlation is based on law of the wall similarity and is the same method employed by Nikuradse for sand-grain roughness. The heat transfer correlation is based on application of a heat-momentum transfer analogy to flow over a rough surface, which was first used by Dipprey and Sabersky for sand-grain roughness. The correlations are verified with experimental data taken with 0.01 < e/D < 0.04 and 10 < p/e < 40 and covering the range 0.71 < Pr < 37.6. The correlations may be extended to a wider range of e/D by virtue of the law of the wall. The good results obtained in this study, supported by the prior work with sand-grain roughness, offer strong argument for application of the correlating methods to other roughness geometries. The success of the heat-momentum analogy correlation is compared with other methods frequently found in the literature.