Analysis of multiphase flows for functional coatings

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This proposed research program on multiphase flows has been motivated primarily by the substantial and growing interest in applying the emerging suspension thermal spray process to produce so-called "functional" coatings. Conventional thermal spray processes such as plasma and high velocity oxygen fuel (HVOF) are already used extensively in the aerospace, automotive, and power generation industries to apply protective coatings on engine, landing gear, and turbine components that are exposed to heat, corrosion, erosion, and wear. They use particle diameters of tens of microns that are fed into the spray gun and heated and accelerated to high velocities. Recently, substantial research efforts have been applied to emerging suspension thermal spray (STS) systems that deposit much smaller nanoparticles and create coatings with superior performance. In STS, a liquid suspension of dispersed nanoparticles is injected into thermal spray flames, which atomize the suspension droplets. The liquid droplets then evaporate allowing the nanoparticles contained in the droplets to accelerate and melt as in a conventional thermal spray process. This technology shows significant promise to create coatings with feed rates suitable for many industrial applications. For example, the nano-structured coatings deposited by the suspension spraying technique demonstrate remarkable wear resistance, enhanced catalytic behaviour and superior thermal insulation. In STS, coating quality and functionality depend primarily on the suspension penetration into the jet, the primary and secondary atomization of the suspension, and the slurry droplet evaporation. Characterizing the multiphase flow and heat transfer associated with the suspension atomization in an all speed (subsonic to supersonic) flow is a challenging research topic requiring numerical and experimental studies. The proposed research program addresses both these aspects by studying multiscale multiphase spray process flows and the resultant functional coatings. We will explore the development of environmentally friendly durable omniphobic coatings, specifically, superhydrophobic, icephobic, and slippery liquid-infused porous surfaces. The computer codes that we generate to simulate the atomization process in industrial sprays also have broad applications in the design of nozzles for metal powder manufacturing, engine fuel systems, agricultural sprayers, dryers, and inhaled drug delivery systems. We anticipate that the results of this study will facilitate the manufacture of key aerospace components, and have a great impact on the Quebec aerospace industry. The technology will also find many applications in the automotive, power generation, and biomedical industries, all of which are important to the Canadian economy.