Gas flow characteristics in micro-nozzle

This research is aimed at improving the performance of micro-space propulsion and micro-gas turbine generators. Based on the micro-fabrication technology, 3D rectangular cross section micro-convergent-divergent-nozzle was fabricated in silicon wafer. Its width in the throat was 16 μm, the depth was 20 μm and the contraction ratio was 1.625:1. For different inlet/outlet pressure ratio, the volume flow rate characteristics of nitrogen were measured experimentally. The pressure ratio ranged from 1.0 to 5.0, outlet volume flow rate ranged from 0 to 0.2 mL/s and outlet Reynolds number was lower than 500. The gas flow characteristics were analyzed by two numerical simulation methods (finite volume method and Boltzmann Gas Kinetic method). Good agreement between computational results and experimental data was found. The simulation results indicate that the sonic cross section gradually moves to downstream of the throat with the increase of pressure ratio. The flow is accelerated in the downstream of the throat. A Mach number is up to 1.26 near the outlet center cross-section when the pressure ratio is 5.0. The pressure distribution is non-linear. It demonstrates that viscous boundary layer and 3D effects are more predominant in micro-nozzle than those in macro-nozzle.