Numerical investigation of combustion and liquid feedstock in high velocity suspension flame spraying process

Over the last decade the interest in thick nano-structured layers has been increasingly growing. Several new applications, including nanostructured thermoelectric coatings, thermally sprayed photovoltaic systems and solid oxide fuel cells, require reduction of micro-cracking, resistance to thermal shock and/or controlled porosity. The high velocity suspension flame spray (HVSFS) is a promising method to prepare advanced materials from nano-sized particles with unique properties. However, compared to the conventional thermal spray, HVSFS is by far more complex and difficult to control because the liquid feedstock phase undergoes aerodynamic break up and vaporization. The effects of suspension droplet size, injection velocity and mass flow rate were parametrically studied and the results were compared for axial, transverse and external injection. The model consists of several sub-models that include pre-mixed combustion of propane-oxygen, non-premixed ethanol-oxygen combustion, modeling aerodynamic droplet break-up and evaporation, heat and mass transfer between liquid droplets and gas phase. Thereby, the models are giving a detailed description of the relevant set of parameters and suggest a set of optimum spray conditions serving as a fundamental reference to further develop the technology.