Розроблення підходу до розрахунку і оптимізації надзвукового сопла для холодного газодинамічного напилювання

This work investigates the process of powder particle acceleration in a supersonic nozzle for cold gas-dynamic spraying (CGS). The task addressed in the study is predetermined by the lack of established patterns in the comprehensive influence of gas parameters and nozzle geometry on the speed of powder particles at the nozzle outlet, which complicates predicting and controlling the spraying process. A new approach to the design of nozzles for CGS has been proposed and implemented, which allows for targeted optimization of their geometric parameters taking into account the gas parameters at the nozzle inlet. The approach is based on a combination of analytical modeling (isentropic model, particle acceleration model), methods of statistical planning and analysis of experiments (central compositional design, construction of regression equations), and multifactor optimization of nozzle geometry. Regularities have been established between the velocity of aluminum particles with a size of 25 μm at the nozzle outlet and the gas parameters: braking pressure 0.8–2.5 MPa and braking temperature 300–700°C. The calculations also took into account the influence of the nozzle geometry: critical diameter 1.0–3.0 mm, outlet diameter 5.0–10.0 mm, length of the expansion section 80–150 mm. The resulting nozzle and spraying mode ensure that the particles achieve a velocity at the outlet of 596 m/s, which exceeds the required minimum of 550 m/s, at an air flow rate of 1.0 m3/min. The proposed approach could be applied to designing new nozzles for mobile and stationary CGS installations operating on compressed air, nitrogen, or helium with a pressure of 0.6 to 4.0 MPa; in particular, for spraying protective and restorative coatings under conditions of limited gas flow. The results lay out the foundation for developing a software tool or an automated system for designing nozzles for CGS in a wide range of initial gas and powder parameters