A Method for Measuring Contact Angle and the Influence of Surface-Fluid Parameters on the Boiling Heat Transfer Performance

An experimental apparatus and a computational routine were developed and implemented in order to obtain the sessile drop images and the contact angle measurement for different fluids and surface conditions. Moreover, experimental results of heat transfer coefficients (HTCs) during pool boiling of de-ionized water (DI water), Al2O3-DI water- and Fe2O3-DI water-based nanofluids are presented in this paper. Based on these results, the effect of surface roughness and nanofluid concentration on the surface wettability, contact angle, and the heat transfer coefficient was analyzed. The experiments were performed on copper heating surfaces with different roughness values (corresponding to a smooth surface or a rough surface). The coated surfaces were produced by the nanofluid pool boiling process at two different volumetric concentrations. All surfaces were subjected to metallographic, wettability and roughness tests. For smooth surfaces, in comparison to DI water, heat transfer enhancement up to 60% is observed for both nanofluids at low concentrations. As the concentration of the nanofluid increases, the surface roughness increases and the contact angle decreases, characterizing a hydrophilic behavior. The analyses indicate that the boiling process of nanofluid leads to the deposition of a coating layer on the surface, which influences the heat transfer performance in two-phase systems.