The wetting of solids by liquids is an important consideration for heat exchangers as it can have a dramatic impact on heat transfer efficiency. The use of superhygrophobic materials, surfaces or coatings is expected to give rise to next-generation high efficiency heat exchanger designs, and this is particularly the case for geothermal heat exchangers where heat exchanger materials interact with highly corrosive fluids.
In order to address this challenge, a material-by-design approach has been adopted, where nanoscale metal oxides were designed and fabricated to provide improvements to the performance of conventional hygrophobic coatings, as well as bare base materials. Novel superhygrophobic coatings were developed, consisting of a polysiloxane matrix, which provides an inherently water repellent film, and functionalized silica nanoparticles, providing bottom-up roughness. Coatings were applied to aluminum Q-panels, which had top-down engineered roughness, providing a composite structure with dual-scale roughness, necessary for superhygrophobicity. The introduction of coatings with multiple functionalities has resulted in the development of both mechanically resilient and highly repellent coatings for heat transfer applications. The novel coatings survived under prolonged immersion in an acidic water solution without changing their superhygrophobic properties, demonstrating their potential for heat exchanger applications and other applications involving moderately corrosive environments.
Geothermal energy is an excellent source of renewable clean power generation, as well as for heating and cooling. Unlike other renewable energy sources, it is unaffected by local climate conditions. However, the heat exchangers used in geothermal power plants are under constant threat of scale formation and corrosion due to the harsh operational conditions to which they are exposed. Therefore, surface modifications to heat exchanger materials, for example through coatings, are necessary to improving the efficiency and durability of geothermal plant. Coatings with superhygrophobic properties are highly desirable for protecting the base metal/alloy due to their unique self-cleaning, anti-fouling and corrosion inhibition properties. These properties also help to reduce the operational and maintenance costs of the equipment.
