Analysis of Two-phase flows for Spraying Processes

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Thermal sprays are extensively used in the aerospace, automotive, power generation, and biomedical industries to provide protective coatings on landing gear, engine, turbine, and implant components that are exposed to heat, corrosion, and wear. In a conventional thermal spray system such as plasma, high velocity oxygen fuel (HVOF), or cold spray, coating particles with a size of tens of microns are fed into the spray nozzle where they are heated and accelerated to high velocities. Consequently, thermally sprayed coatings are formed by the impact and solidification of a stream of molten or semi-molten particles on a surface. We have designed and built a shroud attachment which considerably expands the capabilities of the HVOF process in the areas of deposition efficiency and flexibility to allow coating with ceramic powders (U.S. Patent No. 6,845,929). In the proposed study, we would like to further expand the capabilities of thermal spray processes by facilitating the injection and deposition of nano and submicron sized coating particles using a suspension feedstock. For this purpose, we need to have a thorough understanding of the atomization and liquid fragmentation in all speed gas flow regimes. The proposed work will address this need through a combined computational and experimental study. Suspension injection will be modelled and characterized to address the need of industries for spraying nanopowders at moderate cost. We expect that the results of this study will facilitate manufacturing 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. Furthermore, a computer code which can simulate the process of atomization in industrial sprays has broad applications in the design of nozzles for delivering fuel in engines, burners, and boilers, as well as for agricultural sprays, dryers, inhaled drug delivery systems, etc.