Effect of Axial and Lateral Magnetic Field Configurations on Heat Transfer in Mixed Convection Ferrofluid Flow

This study investigates the effects of magnetic field orientation and axial extent on convective heat transfer in a laminar flow of water-based ferrofluid through a heated horizontal tube. Experiments were conducted at Reynolds numbers of 109, 150, and 164 using two field configurations: lateral fields, with magnets positioned on opposite sides of the tube with varying polarities, and axial fields, with one to three magnets arranged sequentially underneath the tube to vary the magnetic interaction length. In lateral configurations, the impact on the local Nusselt number was negligible or slightly negative depending on magnet orientation. In contrast, axial configurations demonstrated a clear relationship between the magnetic field interaction length and heat transfer enhancement. The local Nusselt number increased progressively with the number of magnets, reaching a maximum of 28.0% for the triple-magnet configuration at Re = 109. The average improvements in the magnetically influenced region were 6.8%, 10.3%, and 14.7% for the single, double, and triple magnet configurations, respectively. These values resulted from the combined effect of magnetic field geometry and Reynolds number, emphasizing the importance of both interaction length and flow conditions in shaping convective heat transfer in ferronanofluid systems.