In Cold Gas Dynamic Spraying the nozzle is a key part that must be optimized to maximize the injected particle acceleration and improve the coating quality. In this study an axi-symmetric two-dimensional mathematical model is presented and used to predict the flow inside a commercial cold spray nozzle and the particle velocity at the nozzle exit. Comparisons between the model results and the measurements made show that the model allows predicting accurately the particle velocity in the cold spray jet even in the presence of shock waves. The study shows that the particle exit velocity depends on the type of propellant gas used and the stagnation temperature and pressure. Following this work, the design of nozzles for specific applications using this mathematical model can be considered.