Critical Heat Flux Enhancement Through Improved Surface Wettability With Surface Oxides and Nanofluids

Surface wetting characteristics have been shown to affect the critical heat flux (CHF) observed during boiling. Surface oxidation is known to improve the ability of the fluid to wet the surface thus enhancing CHF. Nanofluids have also shown potential to enhance CHF, but the mechanisms are poorly understood. This study is targeted towards investigating whether or not nanofluids improve CHF by altering the surface energy. The surface energy of a heater was altered by oxidizing the surface to varying degrees or depositing metal onto the surface, and was characterized by measuring the advancing three-phase contact angle. Boiling curves were determined for water and ethanol based nanofluids with aluminum oxide nanoparticle concentrations from 0.001 g/l to 0.5 g/l as well as pure fluids on surfaces of varying surface energy. A 2.7 cm² copper heater (polished or oxidized) was used for the water-based measurements. A 1.1 cm² thick-film heater coated with glass and/or gold was used for the ethanol-based measurements. Boiling curves obtained using these fluid/surface combinations are discussed.