Experimental Research on Stability and Natural Convection of TiO2-Water Nanofluid in Enclosures with Different Rotation Angles

The stability and natural convection heat transfer characteristics of TiO2-water nanofluid in enclosures with different rotation angles (α = -45°, α = 0°, α = 45°, and α = 90°) are experimentally investigated. The effects of different pH values and doses (m) of dispersant agent on the stability of TiO2-water nanofluid are investigated. It is found that TiO2-water nanofluid with m = 6 wt% and pH = 8 has the lowest transmittance and has the best stability. The effects of different rotation angles (α = -45°, α = 0°, α = 45°, and α = 90°), nanoparticle mass fractions (wt% = 0.1%, wt% = 0.3%, and wt% = 0.5%) and heating powers (Q = 1 W, Q = 5 W, Q = 10 W, Q = 15 W, and Q = 20 W) on the natural convection heat transfer characteristics are also studied. It is found that the enclosure with rotation angle α = 0° has the highest Nusselt number, followed by the enclosure with rotation angles α = 45° and α = 90°, the enclosure with rotation angle α = -45° has the lowest Nusselt number. It is also found that natural convection heat transfer performance increases with the nanoparticle mass fraction and heating power, but the enhancement ratio decreases with the heating power.