A study of the influence of geometric parameters of a de Laval nozzle on the Cold Spray process

The paper investigates the influence of the geometrical parameters of a de Laval nozzle as well as the thermodynamic parameter on the particle velocity values obtained for the combined vortex and axial motion during the cold spray process. The analysis involved determining a basic case of a de Laval nozzle, which was then modified. The geometric parameters analyzed were the diameter of the throat and the diameter of the outlet of the nozzle, as well as the length of the divergent part of the nozzle. The diameter of the nozzle throat was 4 mm or 6 mm and the length of the divergent part was 82.4mm to 240mm. For the smaller nozzle throat size, the outlet diameter of the nozzle was tested in the range of 7 mm to 12 mm, while for the larger throat size, it was in the range of 7 mm to 15 mm, with increments of 1 mm for both ranges. The thermodynamic parameter that was taken into account was pressure, and this was tested in the range of 2MPa, to 3MPa, with an increase of 0.5 MPa within this range. The working fluid applied during the simulation was treated with air as an ideal gas, and the selected microparticle material was copper. The microparticles had a spherical shape and a diameter of 20μm. It has been observed that, depending on the pressure introduced, the optimum value of the expansion ratio changes. For a geometry with a diameter of the nozzle throat 6mm and a length of 82.4mm, it has been observed that the range of the optimum value of the expansion ratio varies with a change in pressure. The optimum value of the expansion ratio for a pressure of 2MPa was 3.36, and for a pressure of 2.5MPa it was 4. The values obtained are below the recommended values mentioned in the literature. The analysis showed that the combined method may have other optimum ranges for the expansion ratio, which are not constant and depend on geometric and thermodynamic parameter. •Higher inlet pressure translates into achieving greater velocities of copper particles.•An increase in inlet pressure results in the extremum of maximum copper particle velocity for higher expansion ratio.•As the copper particle size decreases, the maximum particle velocity is achieved for larger nozzle outlet diameters.•As a result of the increase in nozzle length, the maximum velocity is reached at larger nozzle outlet diameters.