Abstract
Suspensions have shown a great potential for being employed as the spraying materials in flame spraying processes with the aim of producing thin and dense coatings. The internal axial injection of a suspension within processes like the high-velocity suspension flame spraying (HVSFS) offers the advantage of complete suspension entrainment within the gas stream, which therefore results in enhanced momentum and heat transfer to the particles. Experimental assessment of the achieved particle velocities and temperatures within the combustion chamber is nonetheless practically infeasible. A better insight into the process is attainable through employing computational simulations. Following a computational fluid dynamic (CFD) modelling approach for HVOF processes, combustion and gas flow turbulences were simulated for different combustion chamber geometries and ethene/oxygen ratios commonly used in the HVSFS process. Simulations were done with the commercial software ANSYS CFX 16.2. To account for the highly turbulent flow characteristics, the k-ε model and the Shear Stress Transport (SST) turbulence model were chosen, employing an eddy-dissipation-model for fuel gas combustion. Second-order upwind discretization was used to enable a good resolution of flow features like shock diamonds. The results of the simulation using different levels of detail of the combustion reaction were compared to experiments employing the modelled combustion chambers and gas flows. Chamber pressure and positions of the shock diamonds were monitored in order to allow a qualitative evaluation of the calculated values.
