Condensation is an important research topic that ensures increased energy efficiency. Our researchers aimed to optimize heat transfer in industrial heat exchanger tubes through surface modification. We first succeeded in fabricating superhydrophilic and superhydrophobic tubes using surface modification. We observed the condensation phenomenon on the outside of the tube and evaluated the heat transfer performance through a condensation experimental facility. As a result, we found that the condensation heat transfer efficiency of superhydrophobic tubes is superior to that of conventional tubes. However, the heat transfer efficiency of the superhydrophobic tube reduced with an increase in saturation. To improve performance degradation, superhydrophilic and superhydrophobic hybrid tubes were fabricated and evaluated for their potential to improve heat transfer efficiency. As a result, we found that the liquid film generated by filmwise condensation on the superhydrophilic surface swept past the residual droplets generated by dropwise condensation on the superhydrophobic surface, resulting in the best heat transfer performance. Our results break the stereotypes of previous studies and provide a new paradigm for achieving optimal heat transfer performance on large-area curved surfaces. This research is expected to be widely applied in a variety of industries where energy efficiency is critical.

In a pilot natural super-hydrophobic surfaces study, a super-hydrophobic surface was made by coating, etching, laser ablation, chemical vapor deposition and lithography. In this study, cone-shaped periodic micro and nano-structures were constructed on a silica surface with femtosecond and picosecond laser, and the period of micro-structures between cone shape patterns was increased with 10 μm intervals. The contact angle and image of the super-hydrophobic surface were analysed and the cone (Aspect-ratio 1.27) shape model with micro-protrusion structure similar to the surface of the lotus leaf was made to measure the contact angle. To analyse the differences in the contact angles between the cone shapes and heights of the micro-protrusion, different samples with cone (Aspect-ratio 1.27), sphere (Aspect-ratio 1.00) shapes were made through laser micro-machining technology. To mimick the natural lotus leaves, the optimum condition was a cone shape. Samples of PDMS with different shapes and mixed micro/nano-structures were fabricated with a PDMS mold insert. The largest contact angle was measured at 170.42° which is similar to the contact angle of the lotus leaf. This mold insert could be used repeatedly. The molding process is advantageous for large areas and mass production.