Numerical Investigation of High Velocity Suspension Flame Spraying
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M. Taleby and S. Hossainpour (Submitted January 31, 2012; in revised form May 15, 2012) High-velocity suspension flame spraying (HVSFS) has recently developed as a possible alternative to conventional HVOF-spraying employing liquid suspensions instead of dry powder feedstock enables the use of nanoparticles. From the fluid dynamics point of view, the HVSFS system is complex and involves three-phase (gas, liquid and solid particles) turbulent flow, heat transfer, evaporation of the suspension solvent, chemical reactions of main fuel (propane) and suspension solvent (ethanol) and supersonic/ subsonic flow transitions. Computational fluid dynamic techniques were carried out to solve the mass, momentum, and energy conservation equations. The realizable k-e turbulence model was used to account for the effect of turbulence. The HVSFS process involves two combustion reactions. A primary combustion process is the premixed oxygen-propane reaction and secondary process is the non-premixed oxygen-gaseous ethanol reaction. For each reaction, one step global reaction, which takes dissociations and intermediate reactions into account, was derived from the equilibrium chemistry code developed by Gordon and McBride and eddy dissipation model was used to calculate the rate of reactions based on the transport equations for all species (10 species) mass fractions. Droplets were tracked in the continuum in a Lagrangian approach. In this paper, flow field inside and outside the gun simulated to provide clear and complete insight about the HVSFS processes. Moreover, the effect of some operative parameters (oxyfuel flow rate, ethanol flow rate, droplets injection velocity and droplets size) on the gas flow field along the centerline and droplets evaporation behavior was discussed.
Keywords
combustion, computational fluid dynamics, ethanol evaporation, high velocity suspension fame spraying (HVSFS)
1. Introduction Thermal spray technology has been utilized for decades successfully and still bears a great potential for new applications in many industrial fields. One of the important advantages is the wide variety of spray materials that can be applied to all kinds of substrate materials. The greatest challenge in thermal spray technologies to date is the fabricating of nanostructured coatings and functional surfaces. The nanostructured coating technology promises an entire new class of coatings with very different physical properties (Ref 1). The microstructure controls many of the physical properties of the coating, presuming a nanoscaled microstructure; one expects superior improvements concerning its mechanical (for example, hardness, Ref 2), chemical (for example, corrosion resistance) and electrical properties. Furthermore, standard spray techniques confront restrictions considering their coating thickness. Spraying of nanoparticles can bridge the gap between thin-film technologies (PVD, CVD) and conventional M. Taleby and S. Hossainpour, Department of Mechanical Engineering, Sahand University of Technology, Tabriz, Iran. Contact e-m
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