Enhancing the Heat Exchanger Performance Through the Use of High Temperature Resistant Superhydrophobic Nanocomposite Coatings

The formation of a condensate film on the surface of a heat exchanger tube reduces the heat transfer coefficient of vapor-to-liquid heat exchangers. This reduction occurs because the thermal conductivity of the condensate liquid is only a fraction of that of the metallic heat exchanging tube material, thereby lowering the overall thermal conductivity. This situation can be overcome if the vapor condensation occurred in the form of droplets, instead of a continuous film. However, to date, it has remained a challenge to promote "dropwise" condensation in practical heat exchangers. This project will develop surface treatment techniques that can lead to superhydrophobicity, resulting in durable dropwise condensation on heat exchanger tubes. In Phase I, two surface treatment techniques were demonstrated, and both led to superhydrophobic surfaces and a dramatic enhancement of the heat transfer rate due to the formation of dropwise condensation. Further, these surfaces maintained dropwise condensation in a high temperature steam environment and exhibited superior durability compared to traditional hydrophobic coatings. Phase II will (1) optimize the superhydrophobic surface treatments; (2) develop variations of the surface treatments for organic systems used in geothermal and solar thermal applications; (3) conduct performance testing of superhydrophobic surface treatments in a test heat exchanger under simulated use conditions; and (4) develop a predictive model for dropwise condensation heat transfer in a multi-tube practical heat exchanger. Commercial Applications and other Benefits as described by the awardee: The development of a durable superhydrophobic surface treatment for heat exchangers should lead to lower electricity costs due to improved heat transfer efficiency and reduced power generation. Superhydrophobic surfaces also should find applications in water-repellant textiles, anti-fouling and anti-corrosion coatings, fluidic drag reduction, oil-water separation, and biomaterials