This paper experimentally investigates the effects of constant magnetic field on the average Nusselt number variation when the water-based ferrofluid with 1 mass% Fe3O4 nanoparticles flows through a helically coiled pipe with constant wall temperature in various Reynolds numbers. The two-step method has been utilized for ferrofluid preparation. In order to increase the heat transfer coefficient of the system, both active and passive methods are employed simultaneously. Changing the pipe shape to a helical configuration and adding magnetic nanoparticles in the fluid flow are two passive methods, while the active method is the exertion of a magnetic field. The convective heat transfer coefficient and pressure drop are two basic criteria in the evaluation of the results, and the main geometrical parameters are curvature and torsion ratios. The effects of fluid flow rate and the strength of the magnetic fields are also investigated. Applying a 600 G constant magnetic field, the results show the average Nusselt number augmentation of nearly 7%. In constant Reynolds number, the stronger magnetic field of 900 G yields a higher average Nusselt number.

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