Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm Experimental study on viscosity of spinel-type manganese ferrite nanofluid in attendance of magnetic field Mohammad Amani a , Pouria Amani b , Alibakhsh Kasaeian c, ⁎ , Omid Mahian d , Fazel Kasaeian e , Somchai Wongwises f a Mechanical and Energy Engineering Department, Shahid Beheshti University, Tehran, Iran b Department of Chemical Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran c Department of Renewable Energies, Faculty of New Science & Technologies, University of Tehran, Tehran, Iran d Young Researchers and Elite Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran e Faculty of Material Science and Engineering, Sharif University of Technology, Tehran, Iran f Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Lab (FUTURE), Department of Mechanical Engineering, Faculty of Engineering, King Mongkut's University of Technology Thonburi (KMUTT), Bangmod, Bangkok, Thailand ARTICLE INFO Keywords: Viscosity MnFe 2 O 4 /water nanofluid Magnetic field Nanoparticle volume fraction ABSTRACT In this paper, an experimental evaluation on the viscosity of water-based manganese ferrite nanofluid with and without magnetic field with 100, 200, 300, and 400 G intensities has been conducted. The Brookfield DV-I PRIME viscometer is implemented to measure the MnFe 2 O 4 /water nanofluid viscosity and to evaluate the influence of different volume concentrations (from 0.25% to 3%) and various temperatures (from 20 to 60 °C) on the viscosity. According to the measurements, viscosity incrementally increases with the augmentation of nanoparticles concentration while it remarkably decreases at higher temperatures under absence and attendance of magnetic field. The maximum viscosity ratio of 1.14 is achieved at 3 vol% of nanoparticles and 20 °C under no magnetic field, whereas it increments to maximum viscosity ratio of 1.75 at 3 vol% of nanoparticles and 40 °C under 400 G magnetic field. Furthermore, new correlation is proposed for determina- tion of viscosity of MnFe 2 O 4 /water nanofluids in terms of magnetic field intensity, volume concentration and temperature. 1. Introduction Nowadays, the incrementing demand of heat transfer fluids has led to development of a fluid with desirable properties, while most of conventional fluids have their deficiencies. To provide superior heat transfer in different applications, Choi [1] introduced such a fluid by stabilizing the colloidal nanosuspension of particles including Al, Al 2 O 3 , CuO, SiO 2 , ZnO, and carbon nanotubes in conventional base fluid including engine oil, ethylene glycol, water, etc. Nanofluids have become the most desirable cooling and heating fluids due to their small dimension and consequently huge ratio of surface to volume which have led to long-term stability, high heat transfer rate, less clogging in flow channel and therefore higher thermal conductivity. The knowledge of thermophysical properties of nanofluids (i.e., thermal conductivity, density, viscosity, and heat capacity) is required before designing a thermal system with the working fluid consisting of nanoparticles. Viscosity is one of the substantial properties since it demonstrates the fluid's resistance and directly influences the convec- tion heat transfer, pressure loss for laminar and turbulent flows, and pumping power. In the literature, numerous investigations have been implemented on analysis of the viscosity of nanofluids to determine the rheological behavior of heat transfer fluids and there is various work on studying the influence of parameters including temperature, volume concentration, particle shape and dimension on the viscosity of nanofluids [2,3]. Magnetic nanofluids—widely known as ferrofluids—are a type of nanofluids that has recently gained significant attention of many researchers [4–6]. Ferrofluids comprise of colloidal magnetic nano- particles prepared in diverse diameters and morphologies from ferro- magnetic materials (i.e., iron, cobalt, nickel etc.) and their oxides (i.e., spinel-type ferrites, magnetite [Fe 3 O 4 ], etc.) and dispersed inside a base fluid, which can be affected under magnetic field. Regarding the measurement of viscosity of ferrofluid, various studies have been conducted [7,8]. An experimental evaluation of viscosity along with http://dx.doi.org/10.1016/j.jmmm.2016.12.129 Received 5 November 2016; Received in revised form 24 December 2016; Accepted 28 December 2016 ⁎ Corresponding author. E-mail addresses: m_amani@sbu.ac.ir (M. Amani), pouria.amani@ut.ac.ir (P. Amani), akasa@ut.ac.ir (A. Kasaeian), omid.mahian@mshdiau.ac.ir (O. Mahian), f.kasa92@student.sharif.edu (F. Kasaeian), somchai.won@kmutt.ac.th (S. Wongwises). Journal of Magnetism and Magnetic Materials 428 (2017) 457–463 Available online 30 December 2016 0304-8853/ © 2016 Elsevier B.V. All rights reserved. MARK