Experimental study on alternating electromagnetic field effect on enhanced heat transfer and the flow analysis of nanofluid

Abstract

The flow characteristics of Fe<inf>3</inf>O<inf>4</inf> nanofluids under alternating electromagnetic fields were examined. Trials involved nanofluids with Reynolds numbers ranging from 5000 to 15,000 and concentrations between 0.5 vol% and 1.5 vol%. Experiments were conducted both with and without electromagnetic fields. The magnetic field of an alternating electromagnetic field enhances the heat transfer coefficient compared to non-electromagnetic cases. This improvement is due to disturbance in the boundary layer and greater local convective heat transfer. Consequently, a high Reynolds number is achieved, though it is reduced at lower Re. Regardless of magnetic field presence, increasing nanoparticle volume fraction improves heat transfer. Higher alternating frequency also enhances heat transfer, though the effect of frequency itself is minimal. A quadratic relationship is observed between magnetic field strength, volume fraction, and heat transfer efficiency. Higher volume fractions and frequencies increase pressure drop and friction factor. Initially, increased frequency and Reynolds number enhance heat transfer, but performance later declines. Magnetic nanoparticles tend to accumulate at the boundary layer, aiding heat transmission and reducing eddy currents. An evaluation index was used to assess overall heat transfer activity. This index rises with increasing Reynolds number and frequency at first but later falls as Reynolds number continues to rise.