Amirkabir University of Technology AUT Journal of Mechanical Engineering 2588-2937 5 3 2021 09 01 Experimental investigation on laminar convective heat transfer of nano ferrofluids under constant and alternating magnetic field 477 494 4158 10.22060/ajme.2020.18628.5908 EN Matin Ghadiri Department of Mechanical Engineering, Shahrood University of Technology, Shahrood, Iran Omid Haghani Department of Mechanical Engineering, Khayyam University, Mashhad, Iran Erfan Emam-jomeh Department of Mechanical Engineering, Khayyam University, Mashhad, Iran Ebrahim Barati Department of Mechanical Engineering, Khayyam University, Mashhad, Iran Journal Article 2020 06 23 Due to unique characteristic behavior of ferrofluids, their rheological and thermophysical properties will be able to change in the external magnetic field. In this paper, the effects of constant and alternating magnetic field on the convective heat transfer coefficient of ferrofluids in a heated circular tube under laminar flow regimes (200≤<em>Re</em>≤1600) are investigated experimentally. The fluids considered in the experiment are distilled water and a Fe₃O₄/water nanofluid with 1% and 3% concentrations by weight (wt%). The obtained results are validated and a good agreement between the experimental data and predicted results is observed. In the absence of a magnetic field, the results illustrate the significant improvement of convective heat transfer for 3 wt% ferrofluid, compared to that of the distilled water as a working fluid. The heat transfer enhancement varies by changing the Reynolds number as well as ferrofluid concentration and the type of applied magnetic field. The results also show that with application of alternating magnetic field with frequency of 50 Hz, the maximum of 5% enhancement in the convective heat transfer coefficient is obtained compared to the case with no magnetic field. https://ajme.aut.ac.ir/article_4158_3e3aa687770f55c704ca997c3be81634.pdf