Heat Transfer Enhancement Using Different SiO₂ Nanofluid Mixing Conditions on a Downward-Facing Heating Surface

This paper discusses the estimation of heat transfer characteristics using different SiO₂ nanofluid conditions on a downward-facing heating surface. Two sizes of SiO₂ nanoparticles (20 and 50 nm) were selected for the nanofluids. The influence of the critical heat flux (CHF) for different nanofluid concentrations was also compared and investigated. We observed that the CHF changed with the concentration of nanofluids, which reached the maximum enhancement at 0.1 g/L but decreased at 0.12 g/L. Compared with reverse osmosis water, the 50- and 20-nm SiO₂ nanofluids exhibited enhancements of approximately 43% and 49%, respectively. The heating surface was characterized and the deposition of nanoparticles was observed. After pool boiling, the wettability of the heating block and the roughness changed. As the concentration increased, the CHF decreased after attaining the maximum value, which was due to the characteristics of the downward-facing heating surface and the decrease in the nucleation points on the heating block surface.