Thermal conductivity and convection heat transfer characteristics of water-Al₂O₃-SDBS nanofluid with the elapse of time

Water-Al₂O₃ nanofluid was manufactured and its thermal conductivity and convection heat transfer characteristics were measured in this study. The measurement was performed at the volumetric concentration of 0.5% and 3% of 20 nm Al₂O₃ nano particles, and mass concentration of 0.1% of SDBS which was applied as a surfactant for the nano particles. An experimental test equipment using transient hot wire method was installed to measure nanofluid thermal conductivity and the measured results were confirmed by measuring pure water with measurement error of 0.92% at 20°C. Another test facility was installed to measure convection heat transfer characteristics. It was designed to simulate a heat sink for a component of electronics cooling system under high heat flux conditions. The thermal conductivity enhancement was up to 11% and convection heat transfer enhancement was up to 2.6% for particle size of 20 nm nanofluids at small time elapse after the nanofluid manufacturing. With the elapse of time after manufacturing nanofluid, thermal conductivity and convection heat transfer enhancement decreased significantly and this trend was measured under all of the measurement conditions. After 24 hours, the enhancement of thermal conductivity and convection heat transfer were less than 1%. After adding SDBS (Sodium DodecylBenzeneSulfonate), the decrease of thermal conductivity and convection heat transfer enhancement with the time elapse was reduced, but the surfactant could not eliminate the diminution.