Yang, Deyu
(2023)
Microstructure and surface design for highly efficient ice mitigation.
PhD thesis, University of Nottingham.
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(Thesis - as examined)
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Abstract
Ice accretion often posed serious operational and safety challenges in a wide range of industries, such as aircraft, wind turbines, power transmission cables, oil field exploration and production and marine transport. Great efforts had been expended to research and develop viable solutions for both active and passive ice prevention. Effective ice protection techniques, however, had yet to be developed due to their deficiencies, such as significant consumption of de-icing chemicals or energy for active methods and poor balance among durable icephobic performance, good environmental resistances, and good mechanical and chemical properties for passive methods. Thus, with the specific surface microstructure design and the deployment of interdisciplinary techniques, this PhD project aimed to research and develop highly efficient ice mitigating strategies. The outcomes of this project committed to widening the vision of the ice mitigating field and minimising the gap between lab research and practical application.
Before the experimental work, a fundamental literature review was conducted about the intrinsic background of ice crystals and iced surfaces, the relationship between hydrophobicity and icephobicity, the current research status of ice mitigation, and the commonly used characterisation and evaluation of icephobicity. Inspired by the talent ideas from literature, the interdisciplinary techniques, powder metallurgy and surface acoustic wave (SAW), were chosen to develop new strategies that covered from dry passive textured surfaces and wet passive icephobic structures to active ice protection with high efficiency.
Through a simple stamping method and chemical vapour deposition, the textured polydimethylsiloxane-184 (PDMS) and 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) -coated coatings with fine and regular texture patterns were developed successfully. The evaluations of surface wettability, water droplet icing, environmental scanning electron microscope (ESEM) icing, and ice adhesion strength demonstrated the good anti/de-icing performance of the prepared coatings. The roles of lowering surface energy and surface texturing for the improvement of hydrophobicity and icephobicity were also discussed and verified accordingly. The relationship between the ice adhesion strength and surface wetting factors gave poor correlations which indicated that the icephobic mechanisms of textured surfaces could not be correlated with single surface wetting parameters or by linear fitting.
With the application of solid sintering, surface functionalisation, and liquid impregnation, two new wet strategies, liquid-impregnated porous metallic structure (LIPMS) and phase change materials (PCM)-impregnation porous metallic structures (PIPMSs), were proposed and fabricated with gradient porosity and hydrophobic/oleophilic guarding design. The evaluation of mechanical properties and repeated anti/de-icing performance showed effective icing delay, good humidity resistance, ultra-low ice adhesion strength (less than 1 kPa), good mechanical properties, durable icephobicity, and improved liquid-maintaining capacity for both LIPMS and PIPMS. Due to the solid properties of PCMs at subzero temperatures, PIPMS had better durable performance and impregnated-material maintaining capacity than LIPMSs.
The surface localised acoustic waves and the acoustic thermal effect of the thin film zinc oxide (ZnO) surface acoustic wave devices demonstrated their excellent potential for active ice mitigations. With the specific surface design, SAW devices were proven to have good anti/de-icing performance with high energy efficiency in a series of active anti/de-icing experiments. The sensitive monitoring of the resonant frequency shifts and their good ice repellency proved SAW devices can be used to design an effective ice monitoring-removing autonomous system. The anti/de-icing work with rime icing on SAW devices revealed the dynamic interfacial behaviour of SAW that the hybrid effect of acoustic waves and the acoustic thermal effect led to the effective anti/de-icing performance.
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