Nanofluids and helical coils are two different techniques to enhance thermal performance of high efficient heat exchangers. By combining these techniques together energy efficiency of equipment could be increased dramatically. In the present work, the forced convective heat transfer and the pressure drop of nanofluid inside helical coils with a constant wall heat flux are studied experimentally. Distilled water was used as a host fluid and Nanofluids of aqueous Al2O3 nanoparticles (35 nm) suspensions were prepared in various volume concentrations of 0.25 ~1.0%. Nanofluids at all concentrations showed much higher heat transfer rate and pressure drop in comparison with distilled water, which is due to the nanoparticles present in the fluid. In addition, due to curvature of coils, significant enhancement was observed in heat transfer rate as well as pressure drop when helical coils utilize instead of straight one. Moreover, the heat transfer rate improved with the increase of pitch coils and decrease of curvature ratio.

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