Effect of surface nanostructure and surface free energy on dropwise condensation heat transfer

Fine polish and oxidation etching method are applied to prepare micro- and nano-structures on copper surfaces. After that, self-assembled monolayers (SAMs) of n-octadecyl mercaptan are coated on. In air circumstance, the contact angle of water on the nano-structured surface (SAM-1) is 160 and that on the finely polished coated surface (SAM-2) is 116. Both coated surfaces have promoted dropwise condensation very well. The condensation heat transfer performance of the SAM-2 is much better than that of the SAM-1. The coordinated effects of difference of surface free energy between nanostructure and liquid-solid on the dropwise condensation heat transfer are analyzed.