Investigation of exhausts from fabricated silicon micronozzles with rectangular and close to rotationally symmetric cross-sections

Abstract

Close to rotationally symmetric in-plane silicon micronozzles with throat and exit diameters of 45 and 260 µm, respectively, have been fabricated using semi-isotropic SF6 etching through an array mask utilizing microloading and reactive ion etching lag. Comparison with nozzles fabricated using deep reactive ion etching (DRIE) and having a rectangular cross-section but a similar hydraulic diameter in the throat, showed that the Reynolds numbers were almost equal even though the DRIE-etched nozzle had an almost five times larger cross-sectional area, hence implying less viscous losses and higher efficiency with the nearly symmetrical nozzles. The nozzle shapes have been studied using x-ray computed tomography. Comparison of the nozzles' exhaust jets using schlieren imaging, showed that the rectangular nozzles' jets deviate from the nozzle axis direction. It is believed that it is caused by the inclined side walls resulting from the DRIE etching. The results from intentionally misaligning the wafers, each containing half a nozzle, 50 µm parallel with or perpendicular to the nozzle axis, showed that the exhaust deviated and widened, respectively. The findings show that the nozzle symmetry affects both the shape and the pointing direction of the exhaust and that schlieren imaging is a powerful tool for determining nozzle thrust vector deviations.

Supersonic jet interactions with a micro-engineered skimmer

“…The structure of micro-jets emanating from nozzles and capillary tubes has been examined using schlieren and shadowgraph imaging to probe density variations, and Pitot tube measurements to interrogate pressure distributions [34][35][36][37][38][39]. For jets expanding at atmospheric pressure, extended multiple shock cell structures have been observed.…”

Systematic variation of design aspects for a significant increase in thermal fracture resistance of alumina microthrusters

“…Small spacecraft also require small propulsion systems to fit the mass requirements [2] and to provide small thrust forces for precise positioning and attitude control [3]. If a thruster either produces thrust in the micro-or milli-Newton range, or is intended for use on a microspacecraft (mass less than 100 kg), it qualifies as a microthruster [4].…”