UC Berkeley

One solution currently being explored for reducing the condensation effects of water inside the evaporator coil of an air conditioning system is the use of textured surface morphologies on the evaporator fins that may enable water droplets to both condense and shed more quickly. While multiple pattern scales and geometries have been characterized on metal substrates, including posts, pillars, post arrays, reentrant structures, micro/nano hierarchical patterns, and microchannels, there is a dearth of research associated with microdome patterns, the significance being that nature’s most famous superhydrophobic, water-shedding surface, the lotus leaf, utilizes these features. Here, aluminum surfaces have been fabricated with varying micropillar and microdome structures and a hydrothermally grown nanoporous layer of zinc oxide to create a hierarchical morphology that is reminiscent of the lotus leaf geometry. Micropillar and microdome array structures with comparable feature sizes and areal densities were fabricated, and their static and dynamic water contact angles were characterized in order to understand the influence of microstructural geometry on water-shedding performance. These hierarchical surfaces were further characterized in dynamic condensing conditions using a custom-designed wind tunnel setup to simulate an air conditioning inlet environment. Video footage was recorded, and an image analysis algorithm was developed and applied in order to compare surface performance. The entire zinc oxide nanostructure synthesis process was then scaled and applied to a full-scale cooling coil for later evaluation in a simulated building testbed. The results of all surface characterization methods and condensation tests, the wind tunnel test bed design, the image analysis algorithm development, and the scaling process are reported.