The miniaturization of electronic devices demands innovative cooling technologies to dissipate the heat over a small area. Dropwise condensation, capable of enhancing heat transfer by an order of magnitude than filmwise condensation, is of great interest for the development of two-phase thermal management systems. Previous research has shown nanoengineered superhydrophobic surfaces are promising to enable sustained dropwise condensation over long duration because these surfaces are usually designed to be Cassie stable and favor the condensate drop departure. However, the air underneath the Cassie drops can act as a barrier to heat transfer and degrade overall heat and mass transfer performance. In this thesis, we aim to investigate the condensation heat transfer on nanostructured superh...[ Read more ]

The miniaturization of electronic devices demands innovative cooling technologies to dissipate the heat over a small area. Dropwise condensation, capable of enhancing heat transfer by an order of magnitude than filmwise condensation, is of great interest for the development of two-phase thermal management systems. Previous research has shown nanoengineered superhydrophobic surfaces are promising to enable sustained dropwise condensation over long duration because these surfaces are usually designed to be Cassie stable and favor the condensate drop departure. However, the air underneath the Cassie drops can act as a barrier to heat transfer and degrade overall heat and mass transfer performance. In this thesis, we aim to investigate the condensation heat transfer on nanostructured superhydrophobic surfaces. Experimental and theoretical studies of dropwise condensation were conducted on both nanostructured superhydrophobic and flat hydrophobic copper surfaces.

Superhydrophobic copper surfaces with nanoribbon structures using wet chemical oxidation followed by fluorization treatment, which yield a water contact angle of 160° and contact angle hysteresis less than 5°. Condensation experiments in ambient condition and environmental scanning electron microscope condition revealed that long duration dropwise condensation were archived and the condensate drop growth cycle of from nucleation to departure was also relatively long on nanostructured surfaces. The heat flux and heat transfer coefficient of dropwise condensation were measured in an in-house built condensation system. The condensate drop growth and departure were recorded simultaneously using a high-speed camera. Our results show the dropwise condensation heat transfer performance on the nanoengineered superhydrophobic surfaces has a ~30% degradation compared with than flat hydrophobic surfaces due to mixtured droplet morphologies on the nanoengineered superhydrophobic surfaces. Applying a single droplet growth model and population balance droplet distribution model, the experimental results were compared with modeling results. Even though the heat transfer model could predict heat transfer performance on flat hydrophobic surface accurately, it failed to perfectly apply to the nanoengineered superhydrophobic surfaces. A more comprehensive model that accounts for the mixtured morphology of condensate drops is recommended for future work.