Effect of the expansion ratio and length ratio on a gas-particle flow in a converging-diverging cold spray nozzle

A cold spray process is a relatively new process that uses high velocity metallic particles for surface modifications. Metallic powder particles are injected into a converging-diverging nozzle and accelerated to supersonic velocities. Gas accelerates in the throat of the nozzle and reaches a maximum speed at the nozzle exit. Due to compression shocks just outside the nozzle, the gas jet has an irregular shape. Experiments on the expansion ratio and the length ratio of the nozzle, particularly in terms of their relation to the gas pressure, temperature and nozzle length, were conducted for the purpose of reducing the shockwave [1].