Enhancement of Nucleate Pool Boiling Heat Transfer on Titanium Oxide Thin Film Surface

This paper presents an experimental study of augmentation of pool boiling heat transfer characteristics of different nanoscale-coated thin film (TF) surfaces using water as boiling liquid at atmospheric pressure. The heating surfaces used for experiments are untreated, treated using emery grits no. 2000 and treated with TiO2 nanoscale coated having thicknesses of 100, 200 and 300 nm thin film surfaces. The thin films were grown on copper substrate by physical vapor deposition method. The surfaces were characterized with respect to contact angle (sessile droplet method), film thickness (thickness monitor) and surface roughness (surface profilometer). The experiments were conducted in a closed boiling vessel at atmospheric pressure. Heat flux was varied from 52.63 to 144.73 W/cm(2). The analysis of experimental data revealed that there is a reduction of about 40.3 % in the incipience superheat for the applied heat for thickest nanoscale coating surface over a untreated surface. It was observed that thin film surface is superior than the treated and untreated surfaces in view of boiling heat transfer coefficient. The maximum of 80.3, 60.2, 29.6, and 11.5 % enhancement in heat transfer coefficient were observed for TiO2 nanoscale-coated TF having thicknesses of 300, 200 and 100 nm and treated surfaces, respectively, compared to untreated surfaces. The highest enhancement of heat transfer coefficient in nanoscale-coated thin film surfaces was due to better liquid spreading, enhanced wettability and active nucleate site density. The maximum uncertainty in heat transfer coefficient was found in the range of +/- 2.69 %.