The microchannel combined hydrophobic nanostructure for enhancing boiling heat transfer

Abstract

Abstract The boiling heat transfer performance of hydrophobic nanostructure decorated microchannel was investigated experimentally to reveal the subtle balancing issues of bubble nucleation sites increase and bubble coalescence delay. Meanwhile the bubble behaviors including bubble nucleation, growth and departure were also studied by high-speed visualization. Microchannel, nanostructure and micro-nano structure were fabricated on pure nickel substrates through the UV-LIGA and electrodeposition techniques. The incipience temperature at the onset of nucleate boiling for smooth surface, microchannel, nanostructure and micro-nano structure were 6.7K, 3.5K, 3.5K and 3.0 K, respectively. Micro-nano structure and smooth surface exhibited the minimum and maximum bubble departure diameter of 1mm and 2.25mm at heat flux of 4 W/cm2. To sum up, nanostructure significantly increased the bubble nucleation sites by reducing the energy barrier of the phase change at low heat flux, while microchannel decreased bubble growth time, and delayed bubble coalescence due to capillary pressure at high heat flux. The utilization of micro-nano structure resulted in to the combined effects of active nucleation sites improvements and bubble coalescence delay, achieving better heat transfer performance.