Effect of stabilizing heat treatment on condensation heat transfer performance of laser micro-/nano-textured copper surface

Abstract

The surface reforming method of metal superhydrophobic surface usually utilizes organic matter, which has the problems of serious environmental pollution, high thermal resistance, low processing efficiency, as well as easy to fall off. According to the application requirements of steam condensation heat transfer on copper surface, a laser micro-/nano-texturing technology assisted by green post-processing method is proposed in this study. In this technology, a nano-second laser was used to texture the surface of pure copper, which will undergo heat treatment to prepare a superhydrophobic surface with micro-/nano-level structures. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze the microstructure changes. A contact angle tester was used to measure the wettability of the surfaces and surface Gibbs energy. Furthermore, steam condensation system was set up to assess surface heat transfer performance. The results show that the laser micro-/nano-textured copper surface has a superhydrophilic contact angle of 4°; after heat treatment, it reaches 161° and became a superhydrophobic surface. As the heat treatment promotes fully oxidation of the textured copper surface, the surface energy is greatly reduced. Due to the formation of nanoscale CuO “clusters” transferred from laser-textured Cu2O by heat treatment, the superhydrophobic surface blocks the growth of condensate droplets and increases the condensation heat transfer coefficient by 4 times to 730.4 W m−2 K−1. It provides a green non-chemical treatment method for heat transfer applications of copper alloy components in the fields of energy, chemical engineering, refrigeration, microelectronics, and batteries.