Effect of surfactants and pH values on stability of γ-Al2O3 nanofluids

Abstract

To greatly improve the thermal performance and critical heat flux of heat transfer, nanofluids are widely used as heat transfer medium in many engineering applications. However, the main challenge is to establish well dispersed nanoparticle systems in base fluids. Therefore, the objective of this study is to evaluate the nanoparticle dispersion in different surfactant modification and pH value. In detail, pure γ-alumina(γ-Al2O3) nanofluids were produced by dispersing γ-Al2O3 nanoparticles in deionized water using a two-step method. Three surfactants (nonionic Tween 60, cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl benzene sulfonate (SBDS)) were respectively selected as an agent for nanofluid quality stabilization. Based on a visual inspection, ζ potential and spectral absorbance analysis, the optimal surfactant concentration and pH value were observed. The results show that the dispersion of γ-Al2O3 nanofluids depends strongly on type and amount of dispersant, the absolute value of ζ potential and the absorbency of γ-Al2O3 nanofluids with CTAB dispersion are highest at the critical micelle concentration. The stability behavior of the nanofluids with different dispersant are also investigated at different pH by the techniques of ζ potential. It was observed that when the pH value is lower than the point of zero charge (PZC), γ-Al2O3 particles are positively charged, and the electrostatic repulsive force between particles is enough to prevent the attraction and collision between particles, ζ potential is at a high level.