Commonly, heat transfer performance of a nanofluid is enhanced by increasing the mass fraction of nanoparticles due to an improvement of the thermo-physical properties. However, increasing the number of nanoparticles in the base fluid will result in an increase of the nanofluid viscosity. This research aims to investigate natural convective heat transfer for an electric heater filled with various Al 2 O 3-water nanofluids. The effects of various mass fractions of the nanofluid (0.1-2.0 wt.%) on the heating efficiency of the electric heater were analyzed over time, and results indicate that the electric heater with the 1.0% Al 2 O 3-water nanofluid has the highest heating efficiency of the external environment.

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