# Numerical Analysis of Cold Spray Process for Creation of Pin Fin Geometries
###### Abstract
The use of a mask for the preparation of nickel electrode surfaces has been previously investigated using the High-Velocity Oxy-Fuel spraying process (HVOF) [18], as well as the atmospheric plasma spray and suspension plasma spray process [19]. Both studies found that the electrodes coated using the mask outperformed the electrode deposited without the mask. This increase in electroactivity was attributed to the different roughness levels achieved from the masked spraying processes. The creation of fin arrays using a mask has also been investigated for the cold spray process. Several studies have analyzed the thermal and hydrodynamic performance of these fin arrays for use in heat exchangers [20; 21; 22; 23; 24; 25; 26]. [PERSON] et al. [20] experimentally analyzed the heat transfer performance of pyramidal and trapezoidal fin arrays made from a masked cold spray process. Aluminum powder was used as the feedstock and deposited on an aluminum substrate using the masked cold spray process. The study found that the thermal performance of the cold-sprayed fin arrays was substantially better than that of traditional machined rectangular fin arrays of similar characteristic dimensions. This increase in performance was believed to be due to the increase in the convective heat transfer coefficient as a result of the increased turbulence between the rows of fins. [PERSON] et al. [21] experimentally analyzed the thermal and hydrodynamic performance of a pyramidal fin array made from a masked cold spray process as well. They analyzed fin arrays made of three different materials (aluminum, nickel, and stainless steel 304), as well as investigated the use of a multi-material fin array to optimize thermal performance for different service temperatures present in heat exchangers. The study found that the generation of the fin arrays created by the masked cold spray process significantly improved the heat transfer performance, due to the increase in the surface roughness of the fins. The cold spray process is intricate, involving multiple disciplines, including fluid mechanics, solid mechanics, and materials science [2; 3; 5; 6; 8; 9; 10; 11; 12; 14; 27; 28; 29; 30]. In the present study, numerical simulations are performed to analyze particle deposition, focusing on creating precise fin-like geometries with an optimal porosity on electrode surfaces by positioning masks between the nozzle and the substrate. Computational Fluid Dynamics (CFD) is employed to simulate the interactions of gas and particles within a high-pressure nozzle, using nickel powder as the feedstock. CFD models are commonly used to optimize nozzle design and predict particle trajectories, velocities, and temperatures in the cold spray process [7; 29; 31; 32; 33; 34; 31; 35; 36; 37; 38; 39; 40; 41; 42; 43]. They offer crucial insights into how process parameters, such as gas pressure and temperature, as well as nozzle design, influence particle velocity and trajectory. These factors directly influence the deposition efficiency and coating quality. In this study, particle in-flight behavior is modeled using a two-way coupled Eulerian-Lagrangian approach, which includes an appropriate drag correlation to account for compressibility and rarefaction effects. A parametric study explores the effects of varying wire thicknesses and opening areas of different masks, inlet pressures and temperatures, standoff distances, and mask positions on the particle conditions upon impact.