SINOPSIS

Experiments with DI-water and two nanofluids having different TiO₂-concentrations have been carried out in pipe flow with inserted twisted tape. No anomalous enhancement of heat transfer was found. It is shown that heat transfer in this specific nanofluid flow is caused by the change of properties alone. With respect to scaling experimental results of nanofluid flow it is argued that evaluation based on Reynolds number alone is misleading. In any case the appropriate Prandtl number representing the actual thermophysical properties has to be considered.