Ahmad Azari

In this work, the experimental heat transfer of metal oxide nanofluids in a plate heat exchanger was investigated. For this purpose, Al2O3
20 and 40 nm?water, TiO2
10–15 and 25 nm?water, and SiO2
20–30 nm?water nanofluids with 0.05, 0.1, and 0.2 wt%of nanoparticle concentration were used to investigate the increment of the heat transfer coefficient for each nanofluid against distilled water. Nanofluid characterization was conducted by dynamic light scattering analysis. Significant enhancements on the heat transfer coefficient in the present nanofluids were observed. The results clearly show that increasing the nanofluid Reynolds number and concentration results in an increase in their heat transfer coefficient. The maximum observed heat transfer enhancement for SiO2 was obtained at 0.2 wt%and Reynolds number  37, which is 2.82. Furthermore, the minimum heat transfer enhancement for Al2O3 (20 nm) was achieved at 0.1 wt%and Reynolds number  158 with 1.64. A new correlation was derived for Nusselt number based on the experimental data of the mentioned nanofluids with an average relative error percentage of 3.78%. Moreover, the variations of Nusselt number vs Peclet number, the overall heat transfer coefficient vs Reynolds number, and the nanofluid friction factor vs Reynolds number were considered, and interesting results were reported.