Thermophysical properties of nanosilica-in-fluid dispersion (nanofluid) derived from rice hull ash.

The study aimed to find an alternative way of enhancing the thermal properties of heat transfer fluids, and utilizing agricultural by-products such as rice hull ash (RHA) which has been proven to be viable and low cost alternative source of nanosilica silica particles. Fluids with nano-scaled particles form a stable suspension and provide impressive improvements in the thermal properties of base fluids. Nanofluid was prepared by dispersing the nanosilica powder from rice hull ash into deionised water as base fluid. SEM analysis of the nanosilica powder gave a size range of 40 to 65 nm. The stability of the nanofluids based on sediment photography and UV-Vis spectrophotometry showed that nanofluids of 1, 2 and 3% volume concentration were stable and without significant sedimentation for 5 d compared to nanofiuids with 4 and 5% volume concentration which were stable for 2 d only. Measured density of the nanofluids did not vary much relative to the base fluid. An increase in dynamic viscosity was observed in nanosilica-in-fluid dispersion (nanofluids) by as much as 202%. Measured specific heat of the nanofluids formulated in five volume concentrations decreased by 3-25% compared to base fluid. The enhancement of thermal conductivity of water reached 50% after dispersing nanosilica powder at different volume concentrations measured at temperatures ranging 30-70 degrees C. The enhancement of thermophysical properties of nanosilica-in-fluid dispersion suggest the potential use of the nanofluids as a heat transfer fluid.