Enhancing the onset of pool boiling by wettability modification on nanometrically smooth surfaces

Pool boiling experiments are performed with degassed water on highly smooth surfaces of two different wettabilities: hydrophilic and hydrophobic cases. Boiling curves and visual observations on the boiling have been performed. The onset of nucleate boiling (ONB) has been measured and the influence of the wettability has been quantified. As the inherent mean roughness of the glass substrates was lower than one nanometer it was possible to show the sole effect of the wettability. No hysteresis in the boiling curve was observed for both cases. The ONB was observed after 3.5°C superheat on the hydrophobic case and the heat transfer coefficient (HTC) changed suddenly from the one of a convection regime (1.5kW/m²K) to the one of a nucleate boiling regime (4kW/m²K). On the contrary for the hydrophilic case, despite superheat above 37°C and presence of boiling, the HTC was kept as the one of the convection regime.