Usefulness of adding magnetic nano-powders to water: Introducing novel criteria for assessing heat transfer applications

Abstract In this study, the usefulness of adding Fe3O4 nanoparticles to water was considered, taking into account the energy demand management. Based on experimental measurements, an increase of 90% and 130% in thermal conductivity and viscosity has been experienced owing to loading Fe3O4. The nanofluid advantage over base fluid is assessed by evaluating the figure of merit (FOM) proposed by various researchers. Taking into account the Prasher, Garj, Lee and Timofeeva criterion, the use of Fe3O4/water nanofluid is acceptable. According to Tesfai criterion, up to 1 vol%, utilizing Fe3O4/water nanofluid has priority over the base fluid. A novel criterion was derived for assessing the heat transfer potential in a smooth tube subjected to constant surface temperature. It was found that the heat transfer potential depends on the number of transfer units (NTU). For NTU > 5, loading nanoparticles decreased the heat transfer potential up to 11% owing to a decrease in specific heat.