Due to the increased use of cube- and nano-satellites, the demand for micro-propulsion systems has grown, necessitating the optimization of micronozzle design and efficiency. Research on the flow characteristics of micronozzles is currently centered around micro-thruster applications, with the primary objective of achieving uniformity in the flow structure to ensure optimal thruster performance. Conversely, the secondary application involves gas mixture separation, requiring a highly non-uniform species distribution in the flowing mixture. The flow through micronozzles can encompass multiple scales, including continuum, slip, transition, and rarefied gas regions due to their smaller dimensions. The current research commences with numerical studies related to the thruster applications of micronozzles, utilizing classical N-S with a linear slip model, DSMC method, and a hybrid N-S/DSMC based on the continuum breakdown concept. The impact of geometric factors such as the divergence half-angle, throat depth, and expansion ratio is thoroughly analyzed for planar micronozzles, along with considerations of wall temperature conditions. The work also explores the effects of micronozzle geometry and flow parameters on the aerodynamic species separation within a planar nozzle, incorporating linear, bell, and trumpet divergent sections under the presence of carrier gas and back pressure conditions. Subsequently, these studies are extended to include a curved nozzle. The results of this research are anticipated to contribute to the development of improved designs for micronozzles utilized in satellite propulsion and aerodynamic separation processes.