In the present work the influence of curvature ratio and coil pitch for Al2O3/water nanofluid laminar flow on heat transfer behavior and pressure drop through helical coils were investigated experimentally. These experiments were performed for coils with curvature ratio 10 and 20 plus coil pitch 24 and 42. The volume fractions of nanoparticles were 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. Also, the Nusselt numbers fornanofluid flow inside coils was correlated with Helical number, Prandtl number and volume concentration of nanofluid.

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