The heat transfer in a channel with its lower wall mounted with streamwise V-shaped riblets is investigated numerically using a LES approach. Both laminar and turbulent flows are considered. At the riblet wall the turbulent drag is reduced by 6% in comparison to the smooth wall, whereas for laminar flow the riblets lead to a significant drag increase. The effect of riblets on heat transfer is investigated explicitly for small Prandtl numbers Pr and an appropriate correlation is derived. This correlation indicates that the Reynolds analogy is not violated in case of Pr = 1 despite the extraordinary turbulent drag reducing mechanism. The numerical results for drag reduction are in good agreement with available experimental and numerical data, and the results are faced with corresponding heat transfer results found in the literature.

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