Effects of geometrical parameters on the performance of a cold gas micronozzle

Abstract

The area of the exit and throat region of a nozzle play a crucial role in its design. This paper is a report of numerical simulations carried out to investigate the in uence of these parameters on the performance factors of an axisymmetric cold gas nozzle of micron-size throat diameter. It was assumed that the deviations of the ow behavior from that of a continuum ow can be taken care of by applying the rst-order slip boundary conditions at the wall. The solution methodology includes a nite-volume-based numerical procedure based on structured quadrilateral grids. A parametric study reveals that to reach the highest values of the thrust and speci c impulse, one should choose a nozzle with the highest possible throat diameter. However, by increasing the outlet diameter, the thrust initially reaches a maximum and then decreases. In these conditions, the speci c impulse is always a decreasing function of the outlet diameter of the micronozzle. It is also observed that the mass ow rate is an increasing function of both the throat and outlet diameters. In addition, the comparison of the results with and without slip velocity shows that the amounts of the mass ow rate, thrust force, and speci c impulse are higher when the rarefaction e ects are taken into account. Nevertheless, no fundamental di erence is observed in ow physics with and without slip velocity.