Using nano-engineered surfaces to control optical properties for solarthermal management

Abstract

This doctoral thesis has investigated the nanostructure geometry effect on the material’soptical properties for solar-thermal management. This study includes two aspects: solar-thermal desalination and radiative heating and cooling. Both parts include investigating the identification of materials, fabrication of nano/microstructures, and a proof-of-concept demonstration. For solar-thermal desalination, prior experimental studies have focused mainly on the broadband solar absorber. In this thesis, the spectral selective absorber is investigated in detail by combining experimental and computational techniques to achieve high efficiency of solar-thermal desalination. A computational model is developed and validated to understand the nanostructure geometry effects of nickel-infused alumina on solar-thermal energy conversion. Then, a manageable fabrication technique using electrochemical deposition is studied to control the nanostructure geometry achieving spectral-selective optical behavior. Finally, a scalable approach involving the use of wicking materials interfaced with the spectral selective absorber is demonstrated for desalination. This achieves enhanced efficiency compared with the broadband absorber. For radiative heating and cooling, previous studies on daytime radiative cooling typically focused on materials with fixed and cooling-optimized optical properties. In this thesis, the porous polymeric structures with dynamically switchable optical properties have been studied in detail. First, a computational model is developed and validated to investigate the geometry effects of porous polymeric fibers on high-performance solar reflection. Secondly, a fabrication technique using the electrospinning process is studied to control fiber geometry achieving high solar reflection. Lastly, a switchable method for solar-thermal regulation is proposed using porousxiv polymeric layers integrated with a spectral selective absorber. A significant energy reduction is predicted when applied to buildings as roofing materials.