In our recent work, we have undertaken numerical studies of 3D nozzle flows in order to understand the performance of present MEMS propulsion devices. We considered two limiting flow conditions, that is a low pressure case, with a stagnation pressure of 0.1 atm, and a high pressure case with the stagnation pressure of 5 atm. The Direct Simulation Monte Carlo (DSMC) low pressure case was found to be computationally demanding. To establish the reliability of this case, the deterministic as well as statistical errors were analyzed. A Navier Stokes solution was obtained for the high pressure case and compared with an equilibrium version of the DSMC approach. The baseline and modified DSMC techniques were applied to the low pressure case.