ORIGINAL Experimental investigation on forced convection heat transfer of ferrofluid between two-parallel plates Milad Valitabar 1 & Masoud Rahimi 2 & Neda Azimi 1 Received: 22 November 2018 /Accepted: 1 July 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract This study presents an experimental investigation on forced convection heat transfer of ferrofluid between two parallel-plates in the presence of a static magnetic field (SMF). The heat transfer between two parallel-aluminum plates is studied, which heat source with a constant heat flux is applied on the bottom plate. The process of heat transfer is examined for DI-water and ferrofluid in the absence and the presence of the magnetic field. The heat transfer characteristics at the different flow rates, magnet distance from the test section (d = 2–80 mm) and nanoparticle volume fractions (ϕ = 0.25–2%wt) are compared to those of pure water. The results depicted that the heat transfer coefficient (h) and Nusselt number (Nu) of ferrofluid are higher than DI-water. In addition, the results show that applying SMF could enhance the convective heat transfer rate and it decreased by an increase in d that means the decrease in the magnetic field strength. The increase in the nanoparticle volume fraction leads to higher heat transfer enhancement. The maximum value of the heat transfer coefficient and Nusselt number are achieved for SMF with d = 2 mm and ϕ = 1% wt. Nomenclatures B Magnetic field induction (mT) C p Specific heat (J/kg.°C) D h Hydraulic diameter of the microchannel (m) h Convective heat transfer coefficient (W/m 2 . °C) K Thermal conductivity of fluid (W/m.°C) Nu Nusselt number (-) Q Total heat power (W) q” Heat flux based on thermal power (W/m 2 ) T Temperature (°C) m ˙ The mass flow rate of fluid flow (kg/s) U Fluid velocity (m/s) Greek letters ϕ Volume fraction of nanoparticles (-) μ f Viscosity of based-fluid (Pa s) μ ff Viscosity of ferrofluid (Pa s) ρ f Density of based-fluid (kg/m 3 ) ρ ff Density of ferrofluid (kg/m 3 ) ρ p Density of Fe 3 O 4 nanoparticles (kg/m 3 ) Subscripts Ave Average value b Bulk f Fluid ff Ferrofluid p Particles Acronyms MNPs Magnetic nanoparticles SMF Static magnetic field 1 Introduction Nanofluids are utilized in the vast majority of modern in- dustries due to the high heat transfer rate since they have a better thermal performance compared to base liquids. Ferrofluid (magnetic nanofluids) is a suspension of solid magnetic nanoparticles (MNPs) in a carrier liquid such as water or kerosene [1–5]. The high surface area to volume ratio of nanoparticles (NPs) provides efficient contact sur- face area for conductive heat transfer between the base fluid and NPs, which acts to boost the effective conductiv- ity of the nanofluid [6, 7]. Unlike the nanofluids, when a ferrofluid exposed to an external magnetic field, it is mag- netized as MNPs align with the magnetic field. The behav- ior of ferrofluid flow and the temperature distribution could be controlled by applying an external magnetic field * Neda Azimi neda.azimi66@yahoo.com; n.azimi@iauksh.ac.ir 1 Department of Chemical Engineering, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran 2 CFD research Center, Chemical Engineering Department, Razi University, Kermanshah, Iran Heat and Mass Transfer https://doi.org/10.1007/s00231-019-02689-9