Investigation on the optical and thermal conductivity characteristics of nanofluid

A renewable power source such as solar energy is one of the possible solutions that could be used to solve the problem of global warming caused by fossil fuels which contributed to a high carbon dioxide emissions. Solar energy is naturally available as it derived from the sun that can be transformed into thermal energy which can be used by human using a device such as solar collector. Conventional heat transfer fluid such as water and ethylene glycol are regarded as poor solar absorber and affect the efficiency of the solar thermal system. Addition of nanoparticles into these fluids can enhance its optical and thermal conductivity. This new generation of heat transfer fluid known as nanofluids. The aims of this study are to investigate theoretically and experimentally the optical and thermal conductivity characteristics of titanium dioxide and aluminium oxide based nanofluids. These two particles were selected due to the availability in market and the classical model of Rayleigh Approach (RA) for optical properties can be applied as their sizes are very small. Effects of surfactant (Gum Arabic, Sodium dodecylbenzenesulfonate; polyvinylpyrrolidone, particle size (<13nm, <21nm and <50 nm), volume percentages of nanoparticles (0.002, 0.004, 0.006, 0.008 and 0.010 vol. %) and pH (3, 5 and 9) on optical properties of nanofluids have also been investigated. Apart from that, the stability of nanofluids was measured through zeta potential measurement and observation. KD2-Pro thermal properties analyzer and UV-Vis spectrophotometer were used to measure the thermal conductivity and optical properties of the samples, respectively. In stability measurement using zeta potential, SDBS surfactant exhibited highest zeta potential compared to other surfactants for both titanium dioxide and aluminium oxide nanofluids. Based on the observation method, titanium dioxide is poor in stability in most of conditions at 0.01% of volume percentages compared to aluminium oxide nanofluids The analytical results based on Rayleigh approach showed that the bigger size (<50nm) of nanoparticles and the larger the volume percentages of nanoparticles (0.010 vol. %) lead to a higher extinction coefficient of both nanofluids. The comparison of extinction coefficient between theoretical and experimental was successfully calculated in this study. All types of nanofluid showed better thermal conductivity compared to distilled water. Titanium dioxide gave the highest enhancement (28.17%) of thermal conductivity compared to base fluid. Finally, titanium dioxide with addition of Gum Arabic surfactant was selected to study the effect of elapse time on nanofluid due to a good stability, optical and thermal conductivity. From this study, thermal conductivity and optical properties of this nanofluid decreased with time within 1 month.