Nanofluids Flow in Laminar to Turbulent Transition Region

Nanofluids (NFs) are considered promising heat transfer carriers for refrigeration and heat power systems. Nanoparticles (NPs) in liquids significantly affect their thermophysical properties. Moreover, the presence of the NPs in the liquid contributes to the increase in both pressure loss and heat transfer coefficients during liquid flow, which cannot be explained by only variation in the NFs’ thermophysical properties. For today, the effect of NPs concentration in liquids on the critical Reynolds number ($\mathrm{Re}_{\mathrm{cr}}$) corresponding to the laminar-turbulent transition has not been examined adequately. Here we demonstrate that there are contradictory experimental results in published studies on the effect of NPs concentration on Re cr corresponding to the laminar-turbulent transition during the liquids flow in channels. There are a number of studies that have experimentally confirmed the acceleration of the laminar-turbulent transition for various NFs with NPs mass fraction increasing. At the same time, there are studies where the laminar-turbulent transition is unchanged or even retarded. In the presented study, the own experimental data on friction factor during flow the NF tetralin/C60 with NPs (C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</inf>) content up to 0.655 mass. % is analysed. It was shown a decrease in the Recr vs. C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</inf> concentration increase. Various hypotheses of the effect of the NPs in the flow liquid on the variation of the $\mathrm{Re}_{\mathrm{cr}}$ are discussed. The obtained results will contribute to improving the understanding of the momentum and heat transport phenomena in nanofluids.