Abstract
In cold spraying, a uniform particle distribution of uniform velocity is desirable to achieve a good quality deposition pattern. Whereas many cold spray facilities use conical convergent-divergent nozzles for accelerating the particles, this paper evaluates a contoured axisymmetric nozzle design to enhance the process efficiency. The performance of a conventional conical cold spray nozzle is compared with that of a new axisymmetric nozzle designed with a smooth throat and contoured for a parallel outflow. The new nozzle profile is obtained by the application of two aerospace design codes based on the Method of Characteristics. A two-way coupled Eulerian-Lagrangian Computational Fluid Dynamics formulation is used, where the continuous phase steady motion is predicted by solving the Reynolds-Averaged Navier-Stokes equations with the Shear Stress Transport k-ω model. A Discrete Phase Model computes the motion of the particles carried by the jet. The numerical predictions show that the new nozzle shape delivers a more radially uniform deposition. A higher particle velocity is also obtained at the same operating conditions used by the industry standard nozzle, which is desirable for good particle bonding to the substrate.
Highlights
Cold spraying is increasingly attractive as a material coating technique, due to its potential applications to a variety of substrate materials [1]
A three-dimensional Computational Fluid Dynamics (CFD) Reynolds-Averaged Navier-Stokes (RANS) model is developed to provide a preliminary assessment of the flow and particle behaviour in a lightly laden jet, in which well-dispersed titanium particles are accelerated by a compressible gas
This comparison indicates that the current CFD model provides a close agreement to the experiment and it is a good platform from which to evaluate the effect of nozzle design improvements
Summary
Cold spraying is increasingly attractive as a material coating technique, due to its potential applications to a variety of substrate materials [1]. Cold spraying consists in accelerating powder particles to a high velocity by a high speed flow. Particle oxidation is avoided, which can make cold spray coatings more durable and with a better bond strength than equivalent plasma sprayed coatings, in some applications. Whereas many cold spray facilities use conical convergent-divergent nozzles for accelerating the particles, it is of interest to consider an alternative workflow to design contoured axisymmetric nozzles that enhance the radial uniformity of the velocity in the carrier phase. The effect of the nozzle cross-section on the particle velocity and distribution was investigated [13,14,15,16]. Other studies have shown that transonic particle drag limits the extent to which the particle velocity can be improved through nozzle redesign [17, 18]. A comparison of the performance of the original and redesigned nozzles is made for the same operating conditions and for the same particle size distribution
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