Thermal performance of Fe3O4/water nanofluid flow in a newly designed dimpled tube under the influence of non-uniform magnetic field

The effects of alternating and constant magnetic fields on heat transfer characteristics of nanofluid flow in a dimpled tube have not been investigated either numerically or experimentally. In this context, the hydrothermal performance of Fe3O4/water (1.0 vol%) ferronanofluid flow in the dimpled tube (P/d = 3.75 and 11.25) has been examined under laminar flow regime (1131 <= Re <= 2102) in this experimental study. While the magnitudes of magnetic fields are 0.16 T, the alternating magnetic field is utilized with square wave type at frequencies of 1, 2, 5 Hz. It is concluded that the dimpled tube causes up to 78.4% increase in Nusselt number compared to the smooth tube, while up to 118.9% increase in Darcy friction factor. The constant magnetic field enhances the Nusselt number up to 4.04% compared to the absence of a magnetic field using ferronanofluid as a working fluid. Higher frequencies of the alternating magnetic field results in higher thermal performance. Alternating magnetic field effect with f = 5 Hz offers 37.3% Nusselt number enhancement compared to the constant magnetic field effect in all tube geometries. It was also seen that P/d = 11.25 gives the highest Performance Evaluation Criteria while the magnetic field effect decreases it in all tube geometries.