(321c) Enhanced Heat Transfer on the Teflon Nanopore Surface Fabricated Using Anodized Alumina Templates.

Advanced energy systems rely on efficient cooling mechanisms for achieving higher power density and system efficiency. Liquid-vapor phase change heat transfer is one of the widely used cooling mechanisms in industries for thermal management. Improving the liquid-vapor phase change heat transfer efficiency could lead to substantial energy savings and reduced greenhouse emissions. Nanopatterning surfaces are known to enhance the liquid-vapor phase change heat transfer in the boiling and quenching regimes. The large surface area and the small features in nanopatterned surfaces allow more active sites for bubble nucleation and faster bubble departing frequency, thereby increasing the heat transfer efficiency. Nanopatterning polymers like Teflon are attractive due to their versatility and chemical resistance to most organic liquids and acids. In this work, we fabricated a Teflon nanopore array by a modified template-assisted pattern transfer technique using anodized aluminum oxide (AAO) as etch masks. The heat transfer performance of the fabricated Teflon nanopores was tested using droplet evaporation experiments with acetone as the working fluid. Traditional pattern transfer techniques using AAO on hydrophobic polymer substrates is limited to a smaller area of pore transfer. We identified the factors that hindered the scale-up process and followed a modified template transfer technique that can improve the pattern transfer on hydrophobic polymers like Teflon. The droplet evaporation experiments performed on the nanopore Teflon surface showed 2.5 times faster droplet evaporation rate than on a flat surface. The increased active sites for bubble nucleation, faster bubble departure frequency, and the increased maximum wetted area due to wet-Cassie type wetting of acetone is responsible for the enhanced heat transfer on the nanoporous Teflon.