The efficacy of magnetic field on the thermal behavior of MnFe₂O₄ nanofluid as a functional fluid through an open-cell metal foam tube

Highlights: • Experiments are performed with MnFe₂O₄ nanofluid through an open-cell metal foam tube. • Effects of concentration, Reynolds number and magnetic field on the nanofluid thermal behavior are examined. • Heat transfer is enhanced in attendance of constant and alternating magnetic fields. - Abstract: In the present experimental study, the influence of permanent and alternating magnetic fields on the flow and thermal behavior of MnFe₂O₄ magnetic nanofluid flowing through a circular open-cell metal foam tube is investigated under homogeneous heat flux conditions. The experiments are performed at various nanoparticle concentrations, Reynolds numbers and magnetic fields with different strengths and frequencies. According to the observations, the heat transfer rate enhances directly relative to nanoparticle concentration and Reynolds number in attendance of magnetic field, whereas its maximum value of 16.4% is found for 2 wt% nanoparticles at Re = 200 under alternating field with 400 G strength and 20 Hz frequency. Moreover, it is observed that the influence of strength and frequency of magnetic field is insignificant for the pressure drop. Hydrothermal efficiency as the ratio of the Nusselt number to the ratio of the pressure drop is defined in order to evaluate the privilege of using MnFe₂O₄ nanofluids in practical applications. The maximum efficiency of 1.25 is observed at 2 wt% under magnetic field with 400 G and 20 Hz at Re = 1000.