الفهرس 
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Abstract
In the present work, the effects of constant, alternating and rotating magnetic fields on the laminar forced convective heat transfer of Fe3O4/water nanofluid (ferrofluid) in a uniformly heated copper tube are investigated experimentally. The local convective heat transfer coefficient is measured in the hydrodynamically fully developed region. A quadrupole magnetic field system has been designed and constructed to generate the constant, alternating and rotating magnetic fields. Different operation modes for the magnetic field system were also examined and the most efficient mode is obtained. The experiments are conducted using ferrofluid with three different mass concentrations of (0.1, 1 and 2.5%) and Reynolds number range of (800 ≤ Re ≤ 2000). Moreover, wide range of parameters such as magnetic field strength (65-950 Gauss), alternating magnetic field frequency (2-40 Hz) and rotating magnetic field speed (60-1200 rpm) were also studied. The primary experiments showed that the Uni-pole magnetic field system provides the maximum heat transfer enhancement. A significant enhancement in the local convective heat transfer of ferrofluid was observed by application of constant magnetic field. Moreover, the results showed that the heat transfer enhancement has a direct relation with the magnetic field intensity, ferrofluid mass concentration and Reynolds number. It was observed that the constant magnetic field has provided a maximum local heat transfer enhancement of 60.2% compared to DI water for ferrofluid with 2.5% mass concentration at Re = 2000. This value is decreased to 51% and 43% by application of rotating and alternating magnetic fields, respectively. Additionally, increasing the alternating magnetic field frequency and the rotating magnetic field speed adversely affects the heat transfer enhancement. For the first time, the magnetic nanofluid bulk flow in a glass tube was recorded under the effect of constant, alternating and rotating magnetic fields. For this purpose, a visualization system was designed and constructed.