ABSTRACT
Many investigators such as Pak and Cho (1998) conducted forced convection experiments using nanofluids and reported abnormal convective heat transfer enhancement (namely, anomalous heat transfer enhancement), in which the measured heat transfer coefficient exceeds the level expected from the increase in the effective thermal properties of nanofluids. This claim has led to a controversial issue, namely, whether or not the anomalous convective heat transfer enhancement is possible in nanofluid convective heat transfer. Prabhat et al. (2012) carried out a detailed analysis examining the database reported in 12 nanofluid papers and found that in nanofluid laminar flows, in fact, there seems to be anomalous heat transfer enhancement in the entrance region. However, the turbulent flow data basically follow Dittus-Boelter’s correlation, once the temperature dependence of viscosity was included in the prediction of the Reynolds number. However, all these findings are not conclusive, because most papers do not report information about the temperature dependence of the viscosity for their nanofluids. Excellent reviews on nanofluid heat transfer investigations for the past decade may be found elsewhere (Ding et al., 2007; Wang and Mujumdar, 2007).
