Thermal Conductivity of Ionic Liquid-Based Nanofluids Containing Magnesium Oxide and Aluminum Oxide Nanoparticles

A promising nanomaterial, magnesium oxide (MgO) and a commonly studied nanomaterial, aluminum oxide (Al2O3) were used to enhance the thermal conductivity of two ionic liquids, i.e., 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCa]) and 1-ethyl-3-methylimidazolium tricyanomethanide ([emim][TCM]) of potential as heat transfer medium. Effects of nanoparticle material, size, shape as well as mass concentration on thermal conductivity enhancement were investigated experimentally, along with stability analysis of the nanoparticle suspensions. The thermal conductivity of [emim][TCM] can be enhanced by up to 40% by adding 15 wt.% of polyhedral MgO nanoparticles. The thermal conductivity of Al2O3 ionanofluids does not vary much with nanoparticle size while that of MgO ionanofluids tends to increase as the nanoparticle size decreases. The Maxwell-Garnett model and the Hamilton–Crosser model could estimate the thermal conductivity of [emim][DCa]-based nanofluids containing Al2O3 and MgO nanoparticles, respectively, while under-prediction prevailed for [emim][TCM]-based nanofluids. Besides, challenges were encountered during zeta potential measurements created by the ionic liquids themselves. New methods need to be developed to correctly measure the zeta potential of ionic liquid-based nanofluids.