Stability Suspension of Al2O3 and ZnO in Ethanol-Water Mixture with Dependence of Sonication Time

Nanofluids are being studied for many heat transfer application in the enhancement of thermal conductivity. The nanoparticles dispersed in the conventional base fluid tend to settle with time and it is one of the challenges for its stability as a heat transfer fluid. Sonication is one of the methods that have been used to increase the dispersion of nanoparticles and increase the nanofluids stability. In this study, stability suspension of alumina (Al2O3) and zinc oxide (ZnO) nanoparticles, of 50 nm and 40 nm respectively, in ethanol-water mixture are observed with dependence of sonication time of 10 minutes, 20 minutes and 30 minutes of probe sonication. Sedimentation method is used to study its stability based on sonication time and the concentration of both nanoparticles of 0.5 wt %, 1 wt % and 3 wt % in the ethanol-water mixture of 0%, 10%, 30%, 50%, 70%, 90% and 100% concentration. Sedimentation test of each sample has been critically checked and recorded. As per result, after 24 hours, nanofluids that has been sonicated for 30 minutes shows higher sedimentation ratio and better stability than samples with 20 minutes sonication. 10 minutes sonicated samples sediment immediately after sonication. At instantaneous time, 50 wt % of ethanol-water mixture is most stable than other range of concentration, and as the nanoparticles concentration increased, the suspension become more stable. However, in a longer period, different ethanol-water concentration exhibit most likely trend by means of stability. By comparison, alumina samples are more stable than ZnO samples. Therefore, the stability suspension of alumina and ZnO without surfactant is affected by sonication time, and the concentration of the nanofluids.