In-situ hierarchical micro/nanocrystals on copper substrate for enhanced boiling performance: An experimental study

Micro/nano structures on the Cu substrate are normally used for the enhancing the heat transfer capacity for many boiling-related applications. Conventional methods for fabricating these structures, however, require additional processing equipment and involve relatively complex processes. In this study, a simple immersion method for generating in-situ micro/nanocrystal structures on Cu substrates is developed for simplifying the fabrication with reduced cost and improving the boiling performance in the meantime. Using characterization analytical instruments including SEM, AFM, XRD, EDS and XPS, the surface morphology and chemical contents of the micro- and nanocrystals generated on the Cu substrate were examined. The experimental results showed that the hierarchical micro/nanocrystals enabled simultaneous enhancements in critical heat flux (CHF) and heat transfer coefficient (HTC), indicating the superiority of the hierarchical micro/nanocrystals in facilitating the boiling performance compared to conventional structured surfaces. It is found that the nanosheet and microflowers (NSMF) surface provides the largest enhancement amongst other micro/ nano structures including the nanograss forests (NG), nanograss forests and micro-petals (NGMP), and nanograss forests and micro-flowers (NGMF). Comparatively, the CHF and HTC could achieve 65.7 W/cm2 and 4.9 W/cm2K, showing an increase of the CHF and HTC by 56.5 % and 170 %, respectively, using the smooth surface in the same condition as the benchmark. It is implied that the liquid circulation is apparently promoted through the separation of vapor-liquid pathway and the bubble blanket formation is remarkably inhibited due to the special structure and morphology of the hierarchical surface. However, vital factors including the surface wettability and the experimental accuracy need to be considered for optimizing the boiling performance in diverse scenarios.