Condensation on amphiphilic surfaces

Rebecca Lynn Winter

doi:10.17918/00000588

Condensation plays a fundamental role in our lives, from the way our climate functions to our ability to generate and use energy. The large amount of energy typically involved in phase change processes means that small improvements in efficiency could translate to impactful energy savings. Condensation can be significantly enhanced by changing the roughness and material of a surface to reduce thermal resistance. Notably, the use of hydrophobic and superhydrophobic materials enhance droplet shedding, which has been found to greatly improve performance. However, neither the most state-of-the-art, nor the simplest and most thoroughly studied of these hydrophobic designs are broadly implemented in real-world systems. These surfaces are often fragile, costly to manufacture, suffer from short usable lives, and can exhibit problematic failure modes. Here, amphiphilic surfaces, characterized by features with both hydrophilic and hydrophobic materials, demonstrate a new approach to the manipulation of wetting behavior and heat transfer. This work focuses on the experimental and analytical study of amphiphilic surfaces for use in condensation. First, an analytical foundation for the wetting behavior and heat transfer on amphiphilic surfaces is developed. The formation and stability of efficient thin filmwise condensation on microamphiphilic and hierarchical amphiphilic surfaces are presented. Next, this work is expanded to use in thermally conductive filmwise condensation on macroscale finned amphiphilic surfaces. A novel dewetting phenomenon is identified and characterized, which promotes cyclical dropwise condensation without the need for an ultrathin hydrophobic coating. Finally, the macroamphiphilic work is extended to use on cylindrical tubes in a controlled condensing environment. Both a stable conductive filmwise mode and a dynamic cyclical drainage mode are identified and characterized on tubes. Both are found to exhibit efficient condensing performance using completely distinct fundamental behaviors, and the cylindrical geometry is determined to offer additional stability to both condensing modes. The use of macroscale features with simple geometries, small dependence on coating thickness, and robustness of wetting dynamics make the work presented here particularly relevant to optimization for real-world application.

Condensation on amphiphilic surfaces

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Condensation on amphiphilic surfaces

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