Gas-atomization of metal is a widely used technique for producing metal powders. The powder produced by the gas-atomization process has many advantages over traditional methods in terms of sphericity, microstructure, morphology, etc. The gas nozzle is the heart of this system. The gas flow field produced by the gas nozzle is characterized by shocks, gas-recirculation, expansion and compression waves, etc. The geometry, profile, orientation, and location of the gas nozzle play a significant role in the performance of the gas nozzle. In this work, a methodology is developed to generate the profile of supersonic annular inclined convergent-divergent gas nozzle specifically for the closed-coupled gas-atomization application. A code is developed using gas dynamics concepts to generate a data-field of geometric and performance parameters of all possible gas nozzles for the given user inputs. The code also predicts the mass median size of particles using empirical correlations for each nozzle profile. From this data-field, one of the gas nozzle geometry is selected for the detailed gas-only numerical study using computational fluid dynamics (CFD). An axisymmetric gas-only numerical study is performed. Argon is considered as the atomizing gas. First, the effect of different gas nozzle expansion configurations (under-expanded, over-expanded, and correctly-expanded) on the gas flow field is studied. Based on this study, a correctly-expanded gas nozzle configuration is selected for further research. In the second part, the effect of different semi-inclination angles of the gas nozzle on the gas flow field is studied for the selected correctly-expanded gas nozzle configuration. This study found that semi-inclination angles between 12 to 18o are suitable for the annular closed-coupled gas-atomization application.