Liquid/surface interaction during pool boiling of DI-water on nanocoated heating surfaces

Abstract

This study focuses on the effect of the nanostructured heating surface on the heat transfer coefficient (HTC) considering the nanofluid concentration used for coating surfaces and the heating surface morphology. Copper blocks with roughness values of Ra = 0.05 μm (smooth surface) and Ra = 0.23 μm (rough surface) were used as heating surfaces, and deionized water (DI-water) at atmospheric pressure and saturation temperature was used as the working fluid. Nanostructured surfaces were obtained by boiling process of Al2O3–DI-water-based nanofluid for different volumetric concentrations 0.0007 vol% and 0.007 vol% (corresponding to low and high nanofluid concentration, respectively) to analyze the interaction between the heating surface and the working fluid. With this purpose, six different copper surfaces were submitted to metallographic, roughness, wettability, and thermal image analysis. The experimental results showed that the enhancement or deterioration of boiling heat transfer is strongly affected by the nanofluid concentration—used to nanocoat the heating surface—and the original heating surface morphology. The nanocoating process increases the surface roughness and changes the surface wettability. Moreover, as the nanofluid concentration increases, the wettability and nanolayer thickness also increase. The wall temperature distribution, obtained by thermal image analysis, agrees with the HTC behavior. For the coated rough surfaces, it is observed deterioration of the HTC regardless of nanofluid concentration. The increase in the surface temperature and the consequent degradation of the HTC are more pronounced for higher nanoparticle concentrations.