Experimental Investigation into Natural Convection of Zinc Oxide/Water Nanofluids in a Square Cavity

The public domain is inundated with discrepancies in numerical and experimental findings on the natural convection heat transfer performance of nanofluids in a cavity. This paper presents the experimental investigation of the natural convection of deionized water (DIW)-based zinc oxide (ZnO) nanofluid in a rectangular cavity. The ZnO nanoparticles (20 nm) were dispersed in DIW to formulate nanofluids at various volume concentrations (0.10, 0.18, 0.36, 0.50 and 1.0 vol.%). The spectrophotometer and zeta potential were used to verify the stability of ZnO/DIW nanofluid at various temperatures and concentrations. ZnO/DIW nanofluids and DIW were charged into a rectangular cavity with the opposite vertical walls under varying temperature differences. The natural convection of ZnO/DIW nanofluid was performed at Rayleigh number range of 7.45 × 107 and 9.20 × 108. Zeta potential values revealed stable nanofluids with no sedimentation of nanoparticles observed within 24 h. At 0.10 vol.% and temperature difference of 32 °C, the ZnO/DIW nanofluid was observed to enhance the heat transfer coefficient by 9.14% relative to DIW. Further increase in volume concentration resulted in the attenuation of heat transfer. Additionally, the Nusselt number and heat transfer rate were augmented by 8.42% and 6.75% at 0.10 vol.%, respectively.