In the second chapter, a foam-core meniscus coating process was developed for retrofitting 100 nm-scale sol-gel anti-reflective coatings onto in-field solar panels through the deposition, evaporation, and curing of wet films.Advantages of this technique include the means to control fluid flow relative to substrate motion and the ability to conform to large, warped substrates. While simple in practice, no models exist for predicting critical outcomes such as film thickness. Preliminary experiments were used to identify important process parameters, and an analytical fluid flow model is developed and validated for predicting the thickness of silica sol–gel films deposited on solar glass. The average model percent error was less than 5\% reflecting good agreement with experimental data. The model is able to adapt to changes in mass loading with the model accurately predicting a nearly linear increase in dry film thickness at higher mass loadings. The model is calibrated and validated across multiple anti-reflective coating recipes.
In the third chapter, a model-based heurestic is proposed to identify feasible diffusion bonding parameters for the manufacture of compact heat exchangers in nuclear power plants. All material, manufacturing and pressure vessel standards requirements for building hybrid compact heat exchangers were identified. Finite element analysis was performed on the heat exchanger structure to help identify a set of diffusion bonding parameters capable of avoiding the constraining failure modes. This approach was validated by fabricating a 316 stainless steel hybrid compact heat exchanger structure useful for coupling supercritical carbon dioxide brayton cycles with sodium-cooled fast reactors for advanced nuclear power applications. To ensure conformity to standards protocol, mechanical testing and metallograhy were performed on diffusion bonded samples in accordance with boiler and pressure vessel standards.
The objective of the fourth chapter is to investigate the role that the surface geometry and spatial frequency plays in the diffusion bonding of cold-rolled surfaces. Diffusion bonding is used to produce compact heat exchangers in a wide variety of materials for many different energy applications. The diffusion bonding process uses high temperature and contact pressure on the two faying sufaces to eliminate pores, or voids, stranded between them. Compact heat exchangers are difficult to diffusion bond as they consist of a stack of laminae with interal channel geometries, which cause non-uniform contact pressure throughout the stack. This variability in contact pressure can cause malformed channels and joint porosity, reducing joint strength and hermeticity and compromising the safety, reliability and performance of the heat exchangers. Several diffusion bonding models exists for ground surfaces, that can predict the resulting percent bonded area (PBA) based on faying surface conditions and diffusion bonding process parameters. Results from these models for non-ground surfaces have shown standard deviations as high as \textpm 25\% percent bonded area on values ranging from 25\% to ~100\% percent bonded area suggesting a lack of fundamental understanding of surface geometry effects on the diffusion bonding process.
Thin 316 stainless steel coupons with both ground and cold-rolled surfaces were extensively characterized using scanning white light interferometry prior to diffusion bonding. Next, the coupons were diffusion bonding to smooth chemomechanically-polished 316 stainless steel samples. Metallography was performed on the diffusion bonding bondline in order to compare the PBA to expected results based on diffusion bonding models from the literature. Finite element analysis is used to gain insights into the effect of plastic dislocation on pore geometries at the start of the diffusion bonding process. New surface metrics are proposed for improving PBA predictions for cold-rolled surfaces.