Stability and sedimentation characteristics of water based Al2O3 and TiO2 nanofluids

Nanofluids are regarded as promising heat transfer fluid due to their ultrafast cooling capability. However, stability analysis of nanofluids is very critical before its application in heat transfer .The present paper reports about an investigation on the stability of water-based Al2O3 and TiO2 nanofluids at ambient temperature. Nanoparticles, namely Al2O3 and TiO2 at different concentrations of 1, 0.5, 0.1, 0.05, and 0.01 wt.% respectively were directly dispersed in water without adding any dispersant and placed in a static container to observe gravitation settling. Change of sedimentation height with respect to time was measured using the sedimentation photograph capturing method. DLS (Dynamic Light Scattering) and zeta potential analysis were also executed to examine the stability of nanofluids. The results show that the visualization method, DLS and zeta potential analysis are in good correspondence to each other. Sedimentation velocity increases with an increase in nanoparticle concentration and aging. Brownian motion of nanoparticles resist the sedimentation in nanofluids. It is observed that TiO2nanofluid is more stable as compared to Al2O3 nanofluid due to its smaller particle size. Finally authors recommend smaller particle size, optimized sonication time, low nanoparticle concentration and use of surfactant to obtain better dispersion stability of nanofluids