Green Synthesis of Al2O3 Nanoparticles for Heat Transfer Nanofluid Utilizing Lemon Extract

To develop new cooling fluids, Al2O3 nanoparticles have been synthesized by environmentally friendly methods (green synthesis). The precursor used was Al(OH)3 extracted from local bauxite. The lemon extract was used as a chelating agent. Al(OH)3 powder was dissolved in water, and then lemon extract was added to it. The mixture solution was heated at 100ºC until the solution forms a gel. The gel was calcined at 1100°C for 1 hour. The calcined product was then crushed to obtain Al2O3 nanoparticles. The powder of Al2O3 nanoparticles was analyzed using X-ray diffraction (XRD) and surface area meter. Nanofluids were prepared from these Al2O3 nanoparticles with a concentration of 1-5g/L. Crystallite size of alpha phase was 37 nm and that of gamma phase was 8 nm. The surface area of Al2O3 nanoparticles was 94.4 m2/g. As calculated from the surface area data, particle size of the nanoparticles was 16 nm. Zeta potential of the nanofluids was -26 to -33 mV. From the results of heat transfer coefficients measurements, it was known that the heat transfer coefficients of the nanofluids were greater than the water one. The increase of the heat transfer coefficient were 17%, 23%, and 27 % for concentrations of 1g / L, 3g / L, and 5g / L, respectively.