Effect of magnetic field on laminar convective heat transfer of magnetite nanofluids

The effect of an external magnetic field on the convective heat transfer and pressure drop of magnetite nanofluids under laminar flow regime conditions (Re < 830) is investigated. Specifically, the influence of magnetic field strength and uniformity on the convective heat transfer coefficient is examined through experiments and supporting simulations of the magnetic flux density distribution and magnetic force acting on nanoparticles. The data show that large enhancement in the local heat transfer coefficient can be achieved by increasing the magnetic field strength and gradient. The convective heat transfer enhancement becomes more pronounced at higher Reynolds numbers, with a four-fold enhancement (i.e., relative to the case with no magnetic field) obtained at Re = 745 and magnetic field gradient of 32.5 mT/mm. The effect of the magnetic field on the pressure drop is not as significant. The pressure drop increases only by up to 7.5% when magnetic field intensity of 430 mT and gradients between 8.6 and 32.5 mT/mm are applied. Based on the simulation results of magnetic field and magnetic force distribution, the mechanisms for heat transfer enhancement are postulated to be accumulation of particles near the magnets (leading to higher thermal conductivity locally), and formation of aggregates acting enhancing momentum and energy transfer in the flow. (C) 2013 Elsevier Ltd. All rights reserved.