Numerical Analysis and Parametric Study of Modified and Benchmark Optimized Cold Spray Designs

The cold spray process has immensely evolved in the past two decades due to its growing applications in additive manufacturing domain. In this process, solid particles are accelerated through high pressure gas above the critical velocities for successful deposition at the substrate surface without melting. The study is aimed at numerically simulating the copper particles impact and critical velocities for subsequent comparison of the existing optimized de Laval nozzle performance with the modified cold spray design at identical input conditions and standoff distance. The modified design is comprised of de Laval nozzle coupled with constant area exit barrel having length range of 50-300 mm to investigate the effects of barrel length variation on particle impact velocity and impact temperature for the range of copper particles sizes. Further to that, modified nozzle divergent segment dimensions are also altered in a way to minimize the effects of shock-expansion formation at the nozzle exit owing to difference of the exit gas pressure with the ambient pressure. Pertinent to highlight that particle impact velocity explicitly does not provide enough details about the efficacy of cold spray process as it hinges on another key parameter known as critical velocity. A positive difference of particle impact to critical velocity dictates the success of cold spray process. Parametric study was carried out for copper particles of 10 - 50 µm diameter sizes for the optimized and modified cold spray designs in ANSYS Fluent using discrete phase modeling approach. Results depict that modified cold spray designs yield better performance in comparison to benchmark optimized design for the complete spectrum of copper particles under investigation. Based on simulation results, it was further examined that modified design performance improves significantly by increasing the length of constant diameter barrel exit which is mainly resulted by increased residence time for gas-particles interaction, hence, ensuring maximal gas momentum transfer to particles.