Numerical and experimental investigations of gas jet used in atomisation of metal powders

Abstract: The environmental impact caused by the traditional production techniques has led to increased research in the field of alternative production techniques such as additive manufacturing. However, the environmental sustainability of the manufacturing techniques that produce and supply powders to the additive manufacturing process can be improved significantly. This project deals with improving the fraction of powder produced by gas atomisation that is suitable for any specific manufacturing process, by optimising the convergent-divergent nozzle used in the process. In order to identify the influential in- put parameters affecting the characteristics of the gas jet exiting a convergent- divergent nozzle, the relative effects of the input parameters were studied. A computational fluid dynamics model of the convergent-divergent nozzle was created and validated using images obtained through the shadow-graph technique. The results of the model and the experiment followed similar trends, but the absolute scale of gas jets did not match. This discrepancy was attributed to assumptions made about the conditions used as inputs to the computational fluid dynamics model, such as gas density and viscosity. Furthermore, a qualitative parametric study performed on the same computational fluid dynamics model revealed that the angle of the nozzle's diverging section to be the most significant parameter that controls the gas jet length.The findings of this study can be used to predict the gas flow through the convergent-divergent nozzle. This will enable more effective design of the gas atomisation process and gas flows in other processes such as in a rocket motor,the lance used in the basic oxygen furnace and the blast furnace tuyere.