There have been many attempts to enhance heat transfer during the condensation (vapor to liquid) process since
condensation is a critical heat transfer mechanism in many industrial processes. One conventional method of
enhancing condensation heat transfer is to specially treat the condensing heat exchanger surface to adequately
promote so-called "dropwise" condensation. Biomimetically constructed coating with hydrophobic materials is
often employed for surface treatment. This coating on the condensing heat transfer surface effectively shifts the
condensation mode from filmwise (the conventional heat transfer mode) to dropwise (similar to lotus leaves?),
resulting in much higher condensation heat transfer. In this method the thickness of coatings is a key parameter
governing the heat transfer rate. Thin coating benefits the heat transfer but can lead to weakening hydrophobicity
and failure to have an acceptable life span. However, thick coating reduces or eliminates the merit of the dropwise
condensation phenomenon because the coating introduces additional thermal resistance. Herein, we report an
innovative biomimetic concept in connection with a surface treatment that potentially solves the aforementioned
issues. Instead of using conventional dense coatings on the condensing surface, the concept of randomly arranged or
structurally oriented nano or submicro-scale fins and/or porous surfaces similar to nature-invented hydrophobic
surfaces allowing molecular clustering for effective steam condensation, is presented and experimentally verified.
The phenomenon of surface wettability has been a contested issue in phase change heat transfer applications. Its research
area has previously broadened in scope from microscale into nanoscale structured surfaces with the aid of high-end
techniques such as nanoelectromechanical system (NEMS) and microelectromechanical system (MEMS). However,
those techniques are both expensive and time-consuming in creating practical nanoscale-structures. In this study, we
propose a streamlined technique to create tunable ultrahydrophobic/philic self-assembled copper oxide nanostructures
with multiple tier roughness. Using a bottom-up process, a fast fabrication time can be achieved (relative to NEMS and
MEMS) through our simple, cost-effective bulk fabrication technique. As demonstrated through the present experiments,
we can control the surface wettability by introducing morphological adaptivity.
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