Analysis of Micro-nozzle Flow Using Navier–Stokes and DSMC Method and Locating the Separation Plane Based on Modified Knudsen Number

The flow through a micro-nozzle was studied using the particle-based DSMC approach and continuum approach using Navier–Stokes. Slip and no-slip boundary conditions are examined for the Navier–Stokes approach. The results are compared with the full DSMC simulation of a micro-nozzle with a 2 µm diameter. Predictions from all three methods are very close in the converging section. However, due to an increase in rarefaction effects, there are variations in the parameters observed at the diverging section of the nozzle. The extent of rarefaction is plotted using the Knudsen number isocurves inside the nozzle. To account for the local variation in characteristics length, Knudsen number is derived based on different properties like pressure, temperature, and density. The Knudsen number isocurves show that the continuum assumption breaks down at the throat, and the effects of rarefaction increase toward the nozzle’s exit.